< draft-ietf-tls-rfc4346-bis   rfc5246.txt 
INTERNET-DRAFT Tim Dierks Network Working Group T. Dierks
Obsoletes (if approved): RFC 3268, 4346, 4366 Independent Request for Comments: 5246 Independent
Updates (if approved): RFC 4492 Eric Rescorla Obsoletes: 3268, 4346, 4366 E. Rescorla
Intended status: Proposed Standard Network Resonance, Inc. Updates: 4492 RTFM, Inc.
<draft-ietf-tls-rfc4346-bis-10.txt> March 2008 (Expires September 2008) Category: Standards Track August 2008
The Transport Layer Security (TLS) Protocol The Transport Layer Security (TLS) Protocol
Version 1.2 Version 1.2
Status of this Memo Status of This Memo
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Copyright Notice
Copyright (C) The IETF Trust (2008). This document specifies an Internet standards track protocol for the
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improvements. Please refer to the current edition of the "Internet
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Abstract Abstract
This document specifies Version 1.2 of the Transport Layer Security This document specifies Version 1.2 of the Transport Layer Security
(TLS) protocol. The TLS protocol provides communications security (TLS) protocol. The TLS protocol provides communications security
over the Internet. The protocol allows client/server applications to over the Internet. The protocol allows client/server applications to
communicate in a way that is designed to prevent eavesdropping, communicate in a way that is designed to prevent eavesdropping,
tampering, or message forgery. tampering, or message forgery.
Table of Contents Table of Contents
1. Introduction 4 1. Introduction ....................................................4
1.1. Requirements Terminology 5 1.1. Requirements Terminology ...................................5
1.2. Major Differences from TLS 1.1 5 1.2. Major Differences from TLS 1.1 .............................5
2. Goals 6 2. Goals ...........................................................6
3. Goals of This Document 7 3. Goals of This Document ..........................................7
4. Presentation Language 7 4. Presentation Language ...........................................7
4.1. Basic Block Size 7 4.1. Basic Block Size ...........................................7
4.2. Miscellaneous 7 4.2. Miscellaneous ..............................................8
4.3. Vectors 8 4.3. Vectors ....................................................8
4.4. Numbers 9 4.4. Numbers ....................................................9
4.5. Enumerateds 9 4.5. Enumerateds ................................................9
4.6. Constructed Types 10 4.6. Constructed Types .........................................10
4.6.1. Variants 10 4.6.1. Variants ...........................................10
4.7. Cryptographic Attributes 11 4.7. Cryptographic Attributes ..................................12
4.8. Constants 13 4.8. Constants .................................................14
5. HMAC and the Pseudorandom Function 14 5. HMAC and the Pseudorandom Function .............................14
6. The TLS Record Protocol 15 6. The TLS Record Protocol ........................................15
6.1. Connection States 16 6.1. Connection States .........................................16
6.2. Record layer 18 6.2. Record Layer ..............................................19
6.2.1. Fragmentation 19 6.2.1. Fragmentation ......................................19
6.2.2. Record Compression and Decompression 20 6.2.2. Record Compression and Decompression ...............20
6.2.3. Record Payload Protection 21 6.2.3. Record Payload Protection ..........................21
6.2.3.1. Null or Standard Stream Cipher 21 6.2.3.1. Null or Standard Stream Cipher ............22
6.2.3.2. CBC Block Cipher 22 6.2.3.2. CBC Block Cipher ..........................22
6.2.3.3. AEAD ciphers 24 6.2.3.3. AEAD Ciphers ..............................24
6.3. Key Calculation 25 6.3. Key Calculation ...........................................25
7. The TLS Handshaking Protocols 26 7. The TLS Handshaking Protocols ..................................26
7.1. Change Cipher Spec Protocol 27 7.1. Change Cipher Spec Protocol ...............................27
7.2. Alert Protocol 27 7.2. Alert Protocol ............................................28
7.2.1. Closure Alerts 28 7.2.1. Closure Alerts .....................................29
7.2.2. Error Alerts 29 7.2.2. Error Alerts .......................................30
7.3. Handshake Protocol Overview 33 7.3. Handshake Protocol Overview ...............................33
7.4. Handshake Protocol 37 7.4. Handshake Protocol ........................................37
7.4.1. Hello Messages 38 7.4.1. Hello Messages .....................................38
7.4.1.1. Hello Request 38 7.4.1.1. Hello Request .............................38
7.4.1.2. Client Hello 39 7.4.1.2. Client Hello ..............................39
7.4.1.3. Server Hello 42 7.4.1.3. Server Hello ..............................42
7.4.1.4 Hello Extensions 43 7.4.1.4. Hello Extensions ..........................44
7.4.1.4.1 Signature Algorithms 45 7.4.1.4.1. Signature Algorithms ...........45
7.4.2. Server Certificate 46 7.4.2. Server Certificate .................................47
7.4.3. Server Key Exchange Message 49 7.4.3. Server Key Exchange Message ........................50
7.4.4. Certificate Request 51 7.4.4. Certificate Request ................................53
7.4.5 Server Hello Done 53 7.4.5. Server Hello Done ..................................55
7.4.6. Client Certificate 53 7.4.6. Client Certificate .................................55
7.4.7. Client Key Exchange Message 55 7.4.7. Client Key Exchange Message ........................57
7.4.7.1. RSA Encrypted Premaster Secret Message 56 7.4.7.1. RSA-Encrypted Premaster Secret Message ....58
7.4.7.2. Client Diffie-Hellman Public Value 58 7.4.7.2. Client Diffie-Hellman Public Value ........61
7.4.8. Certificate verify 59 7.4.8. Certificate Verify .................................62
7.4.9. Finished 60 7.4.9. Finished ...........................................63
8. Cryptographic Computations 62 8. Cryptographic Computations .....................................64
8.1. Computing the Master Secret 62 8.1. Computing the Master Secret ...............................64
8.1.1. RSA 62 8.1.1. RSA ................................................65
8.1.2. Diffie-Hellman 62 8.1.2. Diffie-Hellman .....................................65
9. Mandatory Cipher Suites 63 9. Mandatory Cipher Suites ........................................65
10. Application Data Protocol 63 10. Application Data Protocol .....................................65
11. Security Considerations 63 11. Security Considerations .......................................65
12. IANA Considerations 63 12. IANA Considerations ...........................................65
A. Protocol Data Structures and Constant Values 65 Appendix A. Protocol Data Structures and Constant Values ..........68
A.1. Record Layer 65 A.1. Record Layer ..............................................68
A.2. Change Cipher Specs Message 66 A.2. Change Cipher Specs Message ...............................69
A.3. Alert Messages 66 A.3. Alert Messages ............................................69
A.4. Handshake Protocol 67 A.4. Handshake Protocol ........................................70
A.4.1. Hello Messages 67 A.4.1. Hello Messages .....................................71
A.4.2. Server Authentication and Key Exchange Messages 69 A.4.2. Server Authentication and Key Exchange Messages ....72
A.4.3. Client Authentication and Key Exchange Messages 70 A.4.3. Client Authentication and Key Exchange Messages ....74
A.4.4. Handshake Finalization Message 71 A.4.4. Handshake Finalization Message .....................74
A.5. The Cipher Suite 71 A.5. The Cipher Suite ..........................................75
A.6. The Security Parameters 73 A.6. The Security Parameters ...................................77
A.7. Changes to RFC 4492 74 A.7. Changes to RFC 4492 .......................................78
B. Glossary 74 Appendix B. Glossary ..............................................78
C. Cipher Suite Definitions 79 Appendix C. Cipher Suite Definitions ..............................83
D. Implementation Notes 81 Appendix D. Implementation Notes ..................................85
D.1 Random Number Generation and Seeding 81 D.1. Random Number Generation and Seeding ......................85
D.2 Certificates and Authentication 81 D.2. Certificates and Authentication ...........................85
D.3 Cipher Suites 81 D.3. Cipher Suites .............................................85
D.4 Implementation Pitfalls 81 D.4. Implementation Pitfalls ...................................85
E. Backward Compatibility 84 Appendix E. Backward Compatibility ................................87
E.1 Compatibility with TLS 1.0/1.1 and SSL 3.0 84 E.1. Compatibility with TLS 1.0/1.1 and SSL 3.0 ................87
E.2 Compatibility with SSL 2.0 85 E.2. Compatibility with SSL 2.0 ................................88
E.3. Avoiding Man-in-the-Middle Version Rollback 87 E.3. Avoiding Man-in-the-Middle Version Rollback ...............90
F. Security Analysis 88 Appendix F. Security Analysis .....................................91
F.1. Handshake Protocol 88 F.1. Handshake Protocol ........................................91
F.1.1. Authentication and Key Exchange 88 F.1.1. Authentication and Key Exchange ....................91
F.1.1.1. Anonymous Key Exchange 88 F.1.1.1. Anonymous Key Exchange ....................91
F.1.1.2. RSA Key Exchange and Authentication 89 F.1.1.2. RSA Key Exchange and Authentication .......92
F.1.1.3. Diffie-Hellman Key Exchange with Authentication 89 F.1.1.3. Diffie-Hellman Key Exchange with
F.1.2. Version Rollback Attacks 90 Authentication ............................92
F.1.3. Detecting Attacks Against the Handshake Protocol 91 F.1.2. Version Rollback Attacks ...........................93
F.1.4. Resuming Sessions 91 F.1.3. Detecting Attacks Against the Handshake Protocol ...94
F.2. Protecting Application Data 91 F.1.4. Resuming Sessions ..................................94
F.3. Explicit IVs 92 F.2. Protecting Application Data ...............................94
F.4. Security of Composite Cipher Modes 92 F.3. Explicit IVs ..............................................95
F.5 Denial of Service 93 F.4. Security of Composite Cipher Modes ........................95
F.6 Final Notes 93 F.5. Denial of Service .........................................96
F.6. Final Notes ...............................................96
Normative References ..............................................97
Informative References ............................................98
Working Group Information ........................................101
Contributors .....................................................101
1. Introduction 1. Introduction
The primary goal of the TLS Protocol is to provide privacy and data The primary goal of the TLS protocol is to provide privacy and data
integrity between two communicating applications. The protocol is integrity between two communicating applications. The protocol is
composed of two layers: the TLS Record Protocol and the TLS Handshake composed of two layers: the TLS Record Protocol and the TLS Handshake
Protocol. At the lowest level, layered on top of some reliable Protocol. At the lowest level, layered on top of some reliable
transport protocol (e.g., TCP[TCP]), is the TLS Record Protocol. The transport protocol (e.g., TCP [TCP]), is the TLS Record Protocol.
TLS Record Protocol provides connection security that has two basic The TLS Record Protocol provides connection security that has two
properties: basic properties:
- The connection is private. Symmetric cryptography is used for - The connection is private. Symmetric cryptography is used for
data encryption (e.g., AES [AES], RC4 [SCH] etc.). The keys for data encryption (e.g., AES [AES], RC4 [SCH], etc.). The keys for
this symmetric encryption are generated uniquely for each this symmetric encryption are generated uniquely for each
connection and are based on a secret negotiated by another connection and are based on a secret negotiated by another
protocol (such as the TLS Handshake Protocol). The Record Protocol protocol (such as the TLS Handshake Protocol). The Record
can also be used without encryption. Protocol can also be used without encryption.
- The connection is reliable. Message transport includes a message - The connection is reliable. Message transport includes a message
integrity check using a keyed MAC. Secure hash functions (e.g., integrity check using a keyed MAC. Secure hash functions (e.g.,
SHA-1, etc.) are used for MAC computations. The Record Protocol SHA-1, etc.) are used for MAC computations. The Record Protocol
can operate without a MAC, but is generally only used in this mode can operate without a MAC, but is generally only used in this mode
while another protocol is using the Record Protocol as a transport while another protocol is using the Record Protocol as a transport
for negotiating security parameters. for negotiating security parameters.
The TLS Record Protocol is used for encapsulation of various higher- The TLS Record Protocol is used for encapsulation of various higher-
level protocols. One such encapsulated protocol, the TLS Handshake level protocols. One such encapsulated protocol, the TLS Handshake
Protocol, allows the server and client to authenticate each other and Protocol, allows the server and client to authenticate each other and
to negotiate an encryption algorithm and cryptographic keys before to negotiate an encryption algorithm and cryptographic keys before
the application protocol transmits or receives its first byte of the application protocol transmits or receives its first byte of
data. The TLS Handshake Protocol provides connection security that data. The TLS Handshake Protocol provides connection security that
has three basic properties: has three basic properties:
- The peer's identity can be authenticated using asymmetric, or - The peer's identity can be authenticated using asymmetric, or
public key, cryptography (e.g., RSA [RSA], DSA [DSS], etc.). This public key, cryptography (e.g., RSA [RSA], DSA [DSS], etc.). This
authentication can be made optional, but is generally required for authentication can be made optional, but is generally required for
at least one of the peers. at least one of the peers.
- The negotiation of a shared secret is secure: the negotiated - The negotiation of a shared secret is secure: the negotiated
secret is unavailable to eavesdroppers, and for any authenticated secret is unavailable to eavesdroppers, and for any authenticated
connection the secret cannot be obtained, even by an attacker who connection the secret cannot be obtained, even by an attacker who
can place himself in the middle of the connection. can place himself in the middle of the connection.
- The negotiation is reliable: no attacker can modify the - The negotiation is reliable: no attacker can modify the
negotiation communication without being detected by the parties to negotiation communication without being detected by the parties to
the communication. the communication.
One advantage of TLS is that it is application protocol independent. One advantage of TLS is that it is application protocol independent.
Higher-level protocols can layer on top of the TLS Protocol Higher-level protocols can layer on top of the TLS protocol
transparently. The TLS standard, however, does not specify how transparently. The TLS standard, however, does not specify how
protocols add security with TLS; the decisions on how to initiate TLS protocols add security with TLS; the decisions on how to initiate TLS
handshaking and how to interpret the authentication certificates handshaking and how to interpret the authentication certificates
exchanged are left to the judgment of the designers and implementors exchanged are left to the judgment of the designers and implementors
of protocols that run on top of TLS. of protocols that run on top of TLS.
1.1. Requirements Terminology 1.1. Requirements Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [REQ]. document are to be interpreted as described in RFC 2119 [REQ].
1.2. Major Differences from TLS 1.1 1.2. Major Differences from TLS 1.1
This document is a revision of the TLS 1.1 [TLS1.1] protocol which This document is a revision of the TLS 1.1 [TLS1.1] protocol which
contains improved flexibility, particularly for negotiation of contains improved flexibility, particularly for negotiation of
cryptographic algorithms. The major changes are: cryptographic algorithms. The major changes are:
- The MD5/SHA-1 combination in the pseudorandom function (PRF) has - The MD5/SHA-1 combination in the pseudorandom function (PRF) has
been replaced with cipher suite specified PRFs. All cipher suites been replaced with cipher-suite-specified PRFs. All cipher suites
in this document use P_SHA256. in this document use P_SHA256.
- The MD5/SHA-1 combination in the digitally-signed element has been - The MD5/SHA-1 combination in the digitally-signed element has been
replaced with a single hash. Signed elements now include a field replaced with a single hash. Signed elements now include a field
that explicitly specifies the hash algorithm used. that explicitly specifies the hash algorithm used.
- Substantial cleanup to the client's and server's ability to - Substantial cleanup to the client's and server's ability to
specify which hash and signature algorithms they will accept. Note specify which hash and signature algorithms they will accept.
that this also relaxes some of the constraints on signature and Note that this also relaxes some of the constraints on signature
hash algorithms from previous versions of TLS. and hash algorithms from previous versions of TLS.
- Addition of support for authenticated encryption with additional - Addition of support for authenticated encryption with additional
data modes. data modes.
- TLS Extensions definition and AES Cipher Suites were merged in - TLS Extensions definition and AES Cipher Suites were merged in
from external [TLSEXT] and [TLSAES]. from external [TLSEXT] and [TLSAES].
- Tighter checking of EncryptedPreMasterSecret version numbers. - Tighter checking of EncryptedPreMasterSecret version numbers.
- Tightened up a number of requirements. - Tightened up a number of requirements.
skipping to change at page 6, line 11 skipping to change at page 6, line 13
- Cleaned up description of Bleichenbacher/Klima attack defenses. - Cleaned up description of Bleichenbacher/Klima attack defenses.
- Alerts MUST now be sent in many cases. - Alerts MUST now be sent in many cases.
- After a certificate_request, if no certificates are available, - After a certificate_request, if no certificates are available,
clients now MUST send an empty certificate list. clients now MUST send an empty certificate list.
- TLS_RSA_WITH_AES_128_CBC_SHA is now the mandatory to implement - TLS_RSA_WITH_AES_128_CBC_SHA is now the mandatory to implement
cipher suite. cipher suite.
- Added HMAC-SHA256 cipher suites - Added HMAC-SHA256 cipher suites.
- Removed IDEA and DES cipher suites. They are now deprecated and - Removed IDEA and DES cipher suites. They are now deprecated and
will be documented in a separate document. will be documented in a separate document.
- Support for the SSLv2 backward-compatible hello is now a MAY, not - Support for the SSLv2 backward-compatible hello is now a MAY, not
a SHOULD, with sending it a SHOULD NOT. Support will probably a SHOULD, with sending it a SHOULD NOT. Support will probably
become a SHOULD NOT in the future. become a SHOULD NOT in the future.
- Added limited "fall-through" to the presentation language to allow - Added limited "fall-through" to the presentation language to allow
multiple case arms to have the same encoding. multiple case arms to have the same encoding.
- Added an Implementation Pitfalls sections - Added an Implementation Pitfalls sections
- The usual clarifications and editorial work. - The usual clarifications and editorial work.
2. Goals 2. Goals
The goals of TLS Protocol, in order of their priority, are as The goals of the TLS protocol, in order of priority, are as follows:
follows:
1. Cryptographic security: TLS should be used to establish a secure 1. Cryptographic security: TLS should be used to establish a secure
connection between two parties. connection between two parties.
2. Interoperability: Independent programmers should be able to 2. Interoperability: Independent programmers should be able to
develop applications utilizing TLS that can successfully exchange develop applications utilizing TLS that can successfully exchange
cryptographic parameters without knowledge of one another's code. cryptographic parameters without knowledge of one another's code.
3. Extensibility: TLS seeks to provide a framework into which new 3. Extensibility: TLS seeks to provide a framework into which new
public key and bulk encryption methods can be incorporated as public key and bulk encryption methods can be incorporated as
necessary. This will also accomplish two sub-goals: preventing the necessary. This will also accomplish two sub-goals: preventing
need to create a new protocol (and risking the introduction of the need to create a new protocol (and risking the introduction of
possible new weaknesses) and avoiding the need to implement an possible new weaknesses) and avoiding the need to implement an
entire new security library. entire new security library.
4. Relative efficiency: Cryptographic operations tend to be highly 4. Relative efficiency: Cryptographic operations tend to be highly
CPU intensive, particularly public key operations. For this CPU intensive, particularly public key operations. For this
reason, the TLS protocol has incorporated an optional session reason, the TLS protocol has incorporated an optional session
caching scheme to reduce the number of connections that need to be caching scheme to reduce the number of connections that need to be
established from scratch. Additionally, care has been taken to established from scratch. Additionally, care has been taken to
reduce network activity. reduce network activity.
3. Goals of This Document 3. Goals of This Document
This document and the TLS protocol itself are based on the SSL 3.0 This document and the TLS protocol itself are based on the SSL 3.0
Protocol Specification as published by Netscape. The differences Protocol Specification as published by Netscape. The differences
between this protocol and SSL 3.0 are not dramatic, but they are between this protocol and SSL 3.0 are not dramatic, but they are
significant enough that the various versions of TLS and SSL 3.0 do significant enough that the various versions of TLS and SSL 3.0 do
not interoperate (although each protocol incorporates a mechanism by not interoperate (although each protocol incorporates a mechanism by
which an implementation can back down to prior versions). This which an implementation can back down to prior versions). This
document is intended primarily for readers who will be implementing document is intended primarily for readers who will be implementing
the protocol and for those doing cryptographic analysis of it. The the protocol and for those doing cryptographic analysis of it. The
specification has been written with this in mind, and it is intended specification has been written with this in mind, and it is intended
to reflect the needs of those two groups. For that reason, many of to reflect the needs of those two groups. For that reason, many of
the algorithm-dependent data structures and rules are included in the the algorithm-dependent data structures and rules are included in the
body of the text (as opposed to in an appendix), providing easier body of the text (as opposed to in an appendix), providing easier
access to them. access to them.
This document is not intended to supply any details of service This document is not intended to supply any details of service
definition or of interface definition, although it does cover select definition or of interface definition, although it does cover select
areas of policy as they are required for the maintenance of solid areas of policy as they are required for the maintenance of solid
security. security.
4. Presentation Language 4. Presentation Language
This document deals with the formatting of data in an external This document deals with the formatting of data in an external
representation. The following very basic and somewhat casually representation. The following very basic and somewhat casually
defined presentation syntax will be used. The syntax draws from defined presentation syntax will be used. The syntax draws from
several sources in its structure. Although it resembles the several sources in its structure. Although it resembles the
programming language "C" in its syntax and XDR [XDR] in both its programming language "C" in its syntax and XDR [XDR] in both its
syntax and intent, it would be risky to draw too many parallels. The syntax and intent, it would be risky to draw too many parallels. The
purpose of this presentation language is to document TLS only; it has purpose of this presentation language is to document TLS only; it has
no general application beyond that particular goal. no general application beyond that particular goal.
4.1. Basic Block Size 4.1. Basic Block Size
The representation of all data items is explicitly specified. The The representation of all data items is explicitly specified. The
basic data block size is one byte (i.e., 8 bits). Multiple byte data basic data block size is one byte (i.e., 8 bits). Multiple byte data
items are concatenations of bytes, from left to right, from top to items are concatenations of bytes, from left to right, from top to
bottom. From the bytestream, a multi-byte item (a numeric in the bottom. From the byte stream, a multi-byte item (a numeric in the
example) is formed (using C notation) by: example) is formed (using C notation) by:
value = (byte[0] << 8*(n-1)) | (byte[1] << 8*(n-2)) | value = (byte[0] << 8*(n-1)) | (byte[1] << 8*(n-2)) |
... | byte[n-1]; ... | byte[n-1];
This byte ordering for multi-byte values is the commonplace network This byte ordering for multi-byte values is the commonplace network
byte order or big endian format. byte order or big-endian format.
4.2. Miscellaneous
4.2. Miscellaneous
Comments begin with "/*" and end with "*/". Comments begin with "/*" and end with "*/".
Optional components are denoted by enclosing them in "[[ ]]" double Optional components are denoted by enclosing them in "[[ ]]" double
brackets. brackets.
Single-byte entities containing uninterpreted data are of type Single-byte entities containing uninterpreted data are of type
opaque. opaque.
4.3. Vectors 4.3. Vectors
A vector (single dimensioned array) is a stream of homogeneous data A vector (single-dimensioned array) is a stream of homogeneous data
elements. The size of the vector may be specified at documentation elements. The size of the vector may be specified at documentation
time or left unspecified until runtime. In either case, the length time or left unspecified until runtime. In either case, the length
declares the number of bytes, not the number of elements, in the declares the number of bytes, not the number of elements, in the
vector. The syntax for specifying a new type, T', that is a fixed- vector. The syntax for specifying a new type, T', that is a fixed-
length vector of type T is length vector of type T is
T T'[n]; T T'[n];
Here, T' occupies n bytes in the data stream, where n is a multiple Here, T' occupies n bytes in the data stream, where n is a multiple
of the size of T. The length of the vector is not included in the of the size of T. The length of the vector is not included in the
encoded stream. encoded stream.
In the following example, Datum is defined to be three consecutive In the following example, Datum is defined to be three consecutive
bytes that the protocol does not interpret, while Data is three bytes that the protocol does not interpret, while Data is three
consecutive Datum, consuming a total of nine bytes. consecutive Datum, consuming a total of nine bytes.
opaque Datum[3]; /* three uninterpreted bytes */ opaque Datum[3]; /* three uninterpreted bytes */
Datum Data[9]; /* 3 consecutive 3 byte vectors */ Datum Data[9]; /* 3 consecutive 3 byte vectors */
Variable-length vectors are defined by specifying a subrange of legal Variable-length vectors are defined by specifying a subrange of legal
lengths, inclusively, using the notation <floor..ceiling>. When lengths, inclusively, using the notation <floor..ceiling>. When
these are encoded, the actual length precedes the vector's contents these are encoded, the actual length precedes the vector's contents
in the byte stream. The length will be in the form of a number in the byte stream. The length will be in the form of a number
consuming as many bytes as required to hold the vector's specified consuming as many bytes as required to hold the vector's specified
maximum (ceiling) length. A variable-length vector with an actual maximum (ceiling) length. A variable-length vector with an actual
length field of zero is referred to as an empty vector. length field of zero is referred to as an empty vector.
T T'<floor..ceiling>; T T'<floor..ceiling>;
In the following example, mandatory is a vector that must contain In the following example, mandatory is a vector that must contain
between 300 and 400 bytes of type opaque. It can never be empty. The between 300 and 400 bytes of type opaque. It can never be empty.
actual length field consumes two bytes, a uint16, sufficient to The actual length field consumes two bytes, a uint16, which is
represent the value 400 (see Section 4.4). On the other hand, longer sufficient to represent the value 400 (see Section 4.4). On the
can represent up to 800 bytes of data, or 400 uint16 elements, and it other hand, longer can represent up to 800 bytes of data, or 400
may be empty. Its encoding will include a two-byte actual length uint16 elements, and it may be empty. Its encoding will include a
field prepended to the vector. The length of an encoded vector must two-byte actual length field prepended to the vector. The length of
be an even multiple of the length of a single element (for example, a an encoded vector must be an even multiple of the length of a single
17-byte vector of uint16 would be illegal). element (for example, a 17-byte vector of uint16 would be illegal).
opaque mandatory<300..400>; opaque mandatory<300..400>;
/* length field is 2 bytes, cannot be empty */ /* length field is 2 bytes, cannot be empty */
uint16 longer<0..800>; uint16 longer<0..800>;
/* zero to 400 16-bit unsigned integers */ /* zero to 400 16-bit unsigned integers */
4.4. Numbers 4.4. Numbers
The basic numeric data type is an unsigned byte (uint8). All larger The basic numeric data type is an unsigned byte (uint8). All larger
numeric data types are formed from fixed-length series of bytes numeric data types are formed from fixed-length series of bytes
concatenated as described in Section 4.1 and are also unsigned. The concatenated as described in Section 4.1 and are also unsigned. The
following numeric types are predefined. following numeric types are predefined.
uint8 uint16[2]; uint8 uint16[2];
uint8 uint24[3]; uint8 uint24[3];
uint8 uint32[4]; uint8 uint32[4];
uint8 uint64[8]; uint8 uint64[8];
All values, here and elsewhere in the specification, are stored in All values, here and elsewhere in the specification, are stored in
"network" or "big-endian" order; the uint32 represented by the hex network byte (big-endian) order; the uint32 represented by the hex
bytes 01 02 03 04 is equivalent to the decimal value 16909060. bytes 01 02 03 04 is equivalent to the decimal value 16909060.
Note that in some cases (e.g., DH parameters) it is necessary to Note that in some cases (e.g., DH parameters) it is necessary to
represent integers as opaque vectors. In such cases, they are represent integers as opaque vectors. In such cases, they are
represented as unsigned integers (i.e., leading zero octets are not represented as unsigned integers (i.e., leading zero octets are not
required even if the most significant bit is set). required even if the most significant bit is set).
4.5. Enumerateds 4.5. Enumerateds
An additional sparse data type is available called enum. A field of An additional sparse data type is available called enum. A field of
type enum can only assume the values declared in the definition. type enum can only assume the values declared in the definition.
Each definition is a different type. Only enumerateds of the same Each definition is a different type. Only enumerateds of the same
type may be assigned or compared. Every element of an enumerated must type may be assigned or compared. Every element of an enumerated
be assigned a value, as demonstrated in the following example. Since must be assigned a value, as demonstrated in the following example.
the elements of the enumerated are not ordered, they can be assigned Since the elements of the enumerated are not ordered, they can be
any unique value, in any order. assigned any unique value, in any order.
enum { e1(v1), e2(v2), ... , en(vn) [[, (n)]] } Te; enum { e1(v1), e2(v2), ... , en(vn) [[, (n)]] } Te;
Enumerateds occupy as much space in the byte stream as would its An enumerated occupies as much space in the byte stream as would its
maximal defined ordinal value. The following definition would cause maximal defined ordinal value. The following definition would cause
one byte to be used to carry fields of type Color. one byte to be used to carry fields of type Color.
enum { red(3), blue(5), white(7) } Color; enum { red(3), blue(5), white(7) } Color;
One may optionally specify a value without its associated tag to One may optionally specify a value without its associated tag to
force the width definition without defining a superfluous element. force the width definition without defining a superfluous element.
In the following example, Taste will consume two bytes in the data In the following example, Taste will consume two bytes in the data
stream but can only assume the values 1, 2, or 4. stream but can only assume the values 1, 2, or 4.
enum { sweet(1), sour(2), bitter(4), (32000) } Taste; enum { sweet(1), sour(2), bitter(4), (32000) } Taste;
The names of the elements of an enumeration are scoped within the The names of the elements of an enumeration are scoped within the
defined type. In the first example, a fully qualified reference to defined type. In the first example, a fully qualified reference to
the second element of the enumeration would be Color.blue. Such the second element of the enumeration would be Color.blue. Such
qualification is not required if the target of the assignment is well qualification is not required if the target of the assignment is well
specified. specified.
Color color = Color.blue; /* overspecified, legal */ Color color = Color.blue; /* overspecified, legal */
Color color = blue; /* correct, type implicit */ Color color = blue; /* correct, type implicit */
For enumerateds that are never converted to external representation, For enumerateds that are never converted to external representation,
the numerical information may be omitted. the numerical information may be omitted.
enum { low, medium, high } Amount; enum { low, medium, high } Amount;
4.6. Constructed Types 4.6. Constructed Types
Structure types may be constructed from primitive types for Structure types may be constructed from primitive types for
convenience. Each specification declares a new, unique type. The convenience. Each specification declares a new, unique type. The
syntax for definition is much like that of C. syntax for definition is much like that of C.
struct { struct {
T1 f1; T1 f1;
T2 f2; T2 f2;
... ...
Tn fn; Tn fn;
} [[T]]; } [[T]];
The fields within a structure may be qualified using the type's name, The fields within a structure may be qualified using the type's name,
with a syntax much like that available for enumerateds. For example, with a syntax much like that available for enumerateds. For example,
T.f2 refers to the second field of the previous declaration. T.f2 refers to the second field of the previous declaration.
Structure definitions may be embedded. Structure definitions may be embedded.
4.6.1. Variants 4.6.1. Variants
Defined structures may have variants based on some knowledge that is Defined structures may have variants based on some knowledge that is
available within the environment. The selector must be an enumerated available within the environment. The selector must be an enumerated
type that defines the possible variants the structure defines. There type that defines the possible variants the structure defines. There
must be a case arm for every element of the enumeration declared in must be a case arm for every element of the enumeration declared in
the select. Case arms have limited fall-through: if two case arms the select. Case arms have limited fall-through: if two case arms
follow in immediate succession with no fields in between, then they follow in immediate succession with no fields in between, then they
both contain the same fields. Thus, in the example below, "orange" both contain the same fields. Thus, in the example below, "orange"
and "banana" both contain V2. Note that this is a new piece of syntax and "banana" both contain V2. Note that this is a new piece of
in TLS 1.2. syntax in TLS 1.2.
The body of the variant structure may be given a label for reference. The body of the variant structure may be given a label for reference.
The mechanism by which the variant is selected at runtime is not The mechanism by which the variant is selected at runtime is not
prescribed by the presentation language. prescribed by the presentation language.
struct { struct {
T1 f1; T1 f1;
T2 f2; T2 f2;
.... ....
Tn fn; Tn fn;
skipping to change at page 11, line 47 skipping to change at page 12, line 5
struct { struct {
select (VariantTag) { /* value of selector is implicit */ select (VariantTag) { /* value of selector is implicit */
case apple: case apple:
V1; /* VariantBody, tag = apple */ V1; /* VariantBody, tag = apple */
case orange: case orange:
case banana: case banana:
V2; /* VariantBody, tag = orange or banana */ V2; /* VariantBody, tag = orange or banana */
} variant_body; /* optional label on variant */ } variant_body; /* optional label on variant */
} VariantRecord; } VariantRecord;
4.7. Cryptographic Attributes 4.7. Cryptographic Attributes
The five cryptographic operations digital signing, stream cipher The five cryptographic operations -- digital signing, stream cipher
encryption, block cipher encryption, authenticated encryption with encryption, block cipher encryption, authenticated encryption with
additional data (AEAD) encryption and public key encryption are additional data (AEAD) encryption, and public key encryption -- are
designated digitally-signed, stream-ciphered, block-ciphered, aead- designated digitally-signed, stream-ciphered, block-ciphered, aead-
ciphered, and public-key-encrypted, respectively. A field's ciphered, and public-key-encrypted, respectively. A field's
cryptographic processing is specified by prepending an appropriate cryptographic processing is specified by prepending an appropriate
key word designation before the field's type specification. key word designation before the field's type specification.
Cryptographic keys are implied by the current session state (see Cryptographic keys are implied by the current session state (see
Section 6.1). Section 6.1).
A digitally-signed element is encoded as a struct DigitallySigned: A digitally-signed element is encoded as a struct DigitallySigned:
struct { struct {
SignatureAndHashAlgorithm algorithm; SignatureAndHashAlgorithm algorithm;
opaque signature<0..2^16-1>; opaque signature<0..2^16-1>;
} DigitallySigned; } DigitallySigned;
The algorithm field specifies the algorithm used (see Section The algorithm field specifies the algorithm used (see Section
7.4.1.4.1 for the definition of this field.) Note that the 7.4.1.4.1 for the definition of this field). Note that the
introduction of the algorithm field is a change from previous introduction of the algorithm field is a change from previous
versions. The signature is a digital signature using those versions. The signature is a digital signature using those
algorithms over the contents of the element. The contents themselves algorithms over the contents of the element. The contents themselves
do not appear on the wire but are simply calculated. The length of do not appear on the wire but are simply calculated. The length of
the signature is specified by the signing algorithm and key. the signature is specified by the signing algorithm and key.
In RSA signing, the opaque vector contains the signature generated In RSA signing, the opaque vector contains the signature generated
using the RSASSA-PKCS1-v1_5 signature scheme defined in [PKCS1]. As using the RSASSA-PKCS1-v1_5 signature scheme defined in [PKCS1]. As
discussed in [PKCS1], the DigestInfo MUST be DER [X680] [X690] discussed in [PKCS1], the DigestInfo MUST be DER-encoded [X680]
encoded and for hash algorithms without parameters (which include [X690]. For hash algorithms without parameters (which includes
SHA-1) the DigestInfo.AlgorithmIdentifier.parameters field MUST be SHA-1), the DigestInfo.AlgorithmIdentifier.parameters field MUST be
NULL but implementations MUST accept both without parameters and with NULL, but implementations MUST accept both without parameters and
NULL parameters. Note that earlier versions of TLS used a different with NULL parameters. Note that earlier versions of TLS used a
RSA signature scheme which did not include a DigestInfo encoding. different RSA signature scheme that did not include a DigestInfo
encoding.
In DSA, the 20 bytes of the SHA-1 hash are run directly through the In DSA, the 20 bytes of the SHA-1 hash are run directly through the
Digital Signing Algorithm with no additional hashing. This produces Digital Signing Algorithm with no additional hashing. This produces
two values, r and s. The DSA signature is an opaque vector, as above, two values, r and s. The DSA signature is an opaque vector, as
the contents of which are the DER encoding of: above, the contents of which are the DER encoding of:
Dss-Sig-Value ::= SEQUENCE { Dss-Sig-Value ::= SEQUENCE {
r INTEGER, r INTEGER,
s INTEGER s INTEGER
} }
Note: In current terminology, DSA refers to the Digital Signature Note: In current terminology, DSA refers to the Digital Signature
Algorithm and DSS refers to the NIST standard. In the original Algorithm and DSS refers to the NIST standard. In the original SSL
SSL and TLS specs, "DSS" was used universally. This document and TLS specs, "DSS" was used universally. This document uses "DSA"
uses "DSA" to refer to the algorithm, "DSS" to refer to the to refer to the algorithm, "DSS" to refer to the standard, and it
standard, and uses "DSS" in the code point definitions for uses "DSS" in the code point definitions for historical continuity.
historical continuity.
In stream cipher encryption, the plaintext is exclusive-ORed with an In stream cipher encryption, the plaintext is exclusive-ORed with an
identical amount of output generated from a cryptographically secure identical amount of output generated from a cryptographically secure
keyed pseudorandom number generator. keyed pseudorandom number generator.
In block cipher encryption, every block of plaintext encrypts to a In block cipher encryption, every block of plaintext encrypts to a
block of ciphertext. All block cipher encryption is done in CBC block of ciphertext. All block cipher encryption is done in CBC
(Cipher Block Chaining) mode, and all items that are block-ciphered (Cipher Block Chaining) mode, and all items that are block-ciphered
will be an exact multiple of the cipher block length. will be an exact multiple of the cipher block length.
In AEAD encryption, the plaintext is simultaneously encrypted and In AEAD encryption, the plaintext is simultaneously encrypted and
integrity protected. The input may be of any length and aead-ciphered integrity protected. The input may be of any length, and aead-
output is generally larger than the input in order to accomodate the ciphered output is generally larger than the input in order to
integrity check value. accommodate the integrity check value.
In public key encryption, a public key algorithm is used to encrypt In public key encryption, a public key algorithm is used to encrypt
data in such a way that it can be decrypted only with the matching data in such a way that it can be decrypted only with the matching
private key. A public-key-encrypted element is encoded as an opaque private key. A public-key-encrypted element is encoded as an opaque
vector <0..2^16-1>, where the length is specified by the encryption vector <0..2^16-1>, where the length is specified by the encryption
algorithm and key. algorithm and key.
RSA encryption is done using the RSAES-PKCS1-v1_5 encryption scheme RSA encryption is done using the RSAES-PKCS1-v1_5 encryption scheme
defined in [PKCS1]. defined in [PKCS1].
In the following example In the following example
stream-ciphered struct { stream-ciphered struct {
uint8 field1; uint8 field1;
uint8 field2; uint8 field2;
digitally-signed opaque { digitally-signed opaque {
uint8 field3<0..255>; uint8 field3<0..255>;
uint8 field4; uint8 field4;
}; };
} UserType; } UserType;
The contents of the inner struct (field3 and field4) are used as The contents of the inner struct (field3 and field4) are used as
input for the signature/hash algorithm, and then the entire structure input for the signature/hash algorithm, and then the entire structure
is encrypted with a stream cipher. The length of this structure, in is encrypted with a stream cipher. The length of this structure, in
bytes, would be equal to two bytes for field1 and field2, plus two bytes, would be equal to two bytes for field1 and field2, plus two
bytes for the signature and hash algorithm, plus two bytes for the bytes for the signature and hash algorithm, plus two bytes for the
length of the signature, plus the length of the output of the signing length of the signature, plus the length of the output of the signing
algorithm. This is known because the algorithm and key used for the algorithm. The length of the signature is known because the
signing are known prior to encoding or decoding this structure. algorithm and key used for the signing are known prior to encoding or
decoding this structure.
4.8. Constants 4.8. Constants
Typed constants can be defined for purposes of specification by Typed constants can be defined for purposes of specification by
declaring a symbol of the desired type and assigning values to it. declaring a symbol of the desired type and assigning values to it.
Under-specified types (opaque, variable length vectors, and Under-specified types (opaque, variable-length vectors, and
structures that contain opaque) cannot be assigned values. No fields structures that contain opaque) cannot be assigned values. No fields
of a multi-element structure or vector may be elided. of a multi-element structure or vector may be elided.
For example: For example:
struct { struct {
uint8 f1; uint8 f1;
uint8 f2; uint8 f2;
} Example1; } Example1;
Example1 ex1 = {1, 4}; /* assigns f1 = 1, f2 = 4 */ Example1 ex1 = {1, 4}; /* assigns f1 = 1, f2 = 4 */
5. HMAC and the Pseudorandom Function 5. HMAC and the Pseudorandom Function
The TLS record layer uses a keyed Message Authentication Code (MAC) The TLS record layer uses a keyed Message Authentication Code (MAC)
to protect message integrity. The cipher suites defined in this to protect message integrity. The cipher suites defined in this
document use a construction known as HMAC, described in [HMAC], which document use a construction known as HMAC, described in [HMAC], which
is based on a hash function. Other cipher suites MAY define their own is based on a hash function. Other cipher suites MAY define their
MAC constructions, if needed. own MAC constructions, if needed.
In addition, a construction is required to do expansion of secrets In addition, a construction is required to do expansion of secrets
into blocks of data for the purposes of key generation or validation. into blocks of data for the purposes of key generation or validation.
This pseudo-random function (PRF) takes as input a secret, a seed, This pseudorandom function (PRF) takes as input a secret, a seed, and
and an identifying label and produces an output of arbitrary length. an identifying label and produces an output of arbitrary length.
In this section, we define one PRF, based on HMAC. This PRF with the In this section, we define one PRF, based on HMAC. This PRF with the
SHA-256 hash function is used for all cipher suites defined in this SHA-256 hash function is used for all cipher suites defined in this
document and in TLS documents published prior to this document when document and in TLS documents published prior to this document when
TLS 1.2 is negotiated. New cipher suites MUST explicitly specify a TLS 1.2 is negotiated. New cipher suites MUST explicitly specify a
PRF and in general SHOULD use the TLS PRF with SHA-256 or a stronger PRF and, in general, SHOULD use the TLS PRF with SHA-256 or a
standard hash function. stronger standard hash function.
First, we define a data expansion function, P_hash(secret, data) that First, we define a data expansion function, P_hash(secret, data),
uses a single hash function to expand a secret and seed into an that uses a single hash function to expand a secret and seed into an
arbitrary quantity of output: arbitrary quantity of output:
P_hash(secret, seed) = HMAC_hash(secret, A(1) + seed) + P_hash(secret, seed) = HMAC_hash(secret, A(1) + seed) +
HMAC_hash(secret, A(2) + seed) + HMAC_hash(secret, A(2) + seed) +
HMAC_hash(secret, A(3) + seed) + ... HMAC_hash(secret, A(3) + seed) + ...
Where + indicates concatenation. where + indicates concatenation.
A() is defined as: A() is defined as:
A(0) = seed A(0) = seed
A(i) = HMAC_hash(secret, A(i-1)) A(i) = HMAC_hash(secret, A(i-1))
P_hash can be iterated as many times as is necessary to produce the P_hash can be iterated as many times as necessary to produce the
required quantity of data. For example, if P_SHA256 is being used to required quantity of data. For example, if P_SHA256 is being used to
create 80 bytes of data, it will have to be iterated three times create 80 bytes of data, it will have to be iterated three times
(through A(3)), creating 96 bytes of output data; the last 16 bytes (through A(3)), creating 96 bytes of output data; the last 16 bytes
of the final iteration will then be discarded, leaving 80 bytes of of the final iteration will then be discarded, leaving 80 bytes of
output data. output data.
TLS's PRF is created by applying P_hash to the secret as: TLS's PRF is created by applying P_hash to the secret as:
PRF(secret, label, seed) = P_<hash>(secret, label + seed) PRF(secret, label, seed) = P_<hash>(secret, label + seed)
The label is an ASCII string. It should be included in the exact form The label is an ASCII string. It should be included in the exact
it is given without a length byte or trailing null character. For form it is given without a length byte or trailing null character.
example, the label "slithy toves" would be processed by hashing the For example, the label "slithy toves" would be processed by hashing
following bytes: the following bytes:
73 6C 69 74 68 79 20 74 6F 76 65 73 73 6C 69 74 68 79 20 74 6F 76 65 73
6. The TLS Record Protocol 6. The TLS Record Protocol
The TLS Record Protocol is a layered protocol. At each layer, The TLS Record Protocol is a layered protocol. At each layer,
messages may include fields for length, description, and content. messages may include fields for length, description, and content.
The Record Protocol takes messages to be transmitted, fragments the The Record Protocol takes messages to be transmitted, fragments the
data into manageable blocks, optionally compresses the data, applies data into manageable blocks, optionally compresses the data, applies
a MAC, encrypts, and transmits the result. Received data is a MAC, encrypts, and transmits the result. Received data is
decrypted, verified, decompressed, reassembled, and then delivered to decrypted, verified, decompressed, reassembled, and then delivered to
higher-level clients. higher-level clients.
Four protocols that use the record protocol are described in this Four protocols that use the record protocol are described in this
document: the handshake protocol, the alert protocol, the change document: the handshake protocol, the alert protocol, the change
cipher spec protocol, and the application data protocol. In order to cipher spec protocol, and the application data protocol. In order to
allow extension of the TLS protocol, additional record content types allow extension of the TLS protocol, additional record content types
can be supported by the record protocol. New record content type can be supported by the record protocol. New record content type
values are assigned by IANA in the TLS Content Type Registry as values are assigned by IANA in the TLS Content Type Registry as
described in Section 12. described in Section 12.
Implementations MUST NOT send record types not defined in this Implementations MUST NOT send record types not defined in this
document unless negotiated by some extension. If a TLS document unless negotiated by some extension. If a TLS
implementation receives an unexpected record type, it MUST send an implementation receives an unexpected record type, it MUST send an
unexpected_message alert. unexpected_message alert.
Any protocol designed for use over TLS must be carefully designed to Any protocol designed for use over TLS must be carefully designed to
deal with all possible attacks against it. As a practical matter, deal with all possible attacks against it. As a practical matter,
this means that the protocol designer must be aware of what security this means that the protocol designer must be aware of what security
properties TLS does and does not provide and cannot safely rely on properties TLS does and does not provide and cannot safely rely on
the latter. the latter.
Note in particular that type and length of a record are not protected Note in particular that type and length of a record are not protected
by encryption. If this information is itself sensitive, application by encryption. If this information is itself sensitive, application
designers may wish to take steps (padding, cover traffic) to minimize designers may wish to take steps (padding, cover traffic) to minimize
information leakage. information leakage.
6.1. Connection States 6.1. Connection States
A TLS connection state is the operating environment of the TLS Record A TLS connection state is the operating environment of the TLS Record
Protocol. It specifies a compression algorithm, an encryption Protocol. It specifies a compression algorithm, an encryption
algorithm, and a MAC algorithm. In addition, the parameters for these algorithm, and a MAC algorithm. In addition, the parameters for
algorithms are known: the MAC key and the bulk encryption keys for these algorithms are known: the MAC key and the bulk encryption keys
the connection in both the read and the write directions. Logically, for the connection in both the read and the write directions.
there are always four connection states outstanding: the current read Logically, there are always four connection states outstanding: the
and write states, and the pending read and write states. All records current read and write states, and the pending read and write states.
are processed under the current read and write states. The security All records are processed under the current read and write states.
parameters for the pending states can be set by the TLS Handshake The security parameters for the pending states can be set by the TLS
Protocol, and the ChangeCipherSpec can selectively make either of the Handshake Protocol, and the ChangeCipherSpec can selectively make
pending states current, in which case the appropriate current state either of the pending states current, in which case the appropriate
is disposed of and replaced with the pending state; the pending state current state is disposed of and replaced with the pending state; the
is then reinitialized to an empty state. It is illegal to make a pending state is then reinitialized to an empty state. It is illegal
state that has not been initialized with security parameters a to make a state that has not been initialized with security
current state. The initial current state always specifies that no parameters a current state. The initial current state always
encryption, compression, or MAC will be used. specifies that no encryption, compression, or MAC will be used.
The security parameters for a TLS Connection read and write state are The security parameters for a TLS Connection read and write state are
set by providing the following values: set by providing the following values:
connection end connection end
Whether this entity is considered the "client" or the "server" in Whether this entity is considered the "client" or the "server" in
this connection. this connection.
PRF algorithm PRF algorithm
An algorithm used to generate keys from the master secret (see An algorithm used to generate keys from the master secret (see
Sections 5 and 6.3). Sections 5 and 6.3).
bulk encryption algorithm bulk encryption algorithm
An algorithm to be used for bulk encryption. This specification An algorithm to be used for bulk encryption. This specification
includes the key size of this algorithm, whether it is a block, includes the key size of this algorithm, whether it is a block,
stream, or AEAD cipher, the block size of the cipher (if stream, or AEAD cipher, the block size of the cipher (if
appropriate), and the lengths of explicit and implicit appropriate), and the lengths of explicit and implicit
initialization vectors (or nonces). initialization vectors (or nonces).
MAC algorithm MAC algorithm
An algorithm to be used for message authentication. This An algorithm to be used for message authentication. This
specification includes the size of the value returned by the MAC specification includes the size of the value returned by the MAC
algorithm. algorithm.
compression algorithm compression algorithm
An algorithm to be used for data compression. This specification An algorithm to be used for data compression. This specification
must include all information the algorithm requires to do must include all information the algorithm requires to do
compression. compression.
master secret master secret
A 48-byte secret shared between the two peers in the connection. A 48-byte secret shared between the two peers in the connection.
client random client random
A 32-byte value provided by the client. A 32-byte value provided by the client.
server random server random
A 32-byte value provided by the server. A 32-byte value provided by the server.
These parameters are defined in the presentation language as: These parameters are defined in the presentation language as:
enum { server, client } ConnectionEnd; enum { server, client } ConnectionEnd;
enum { tls_prf_sha256 } PRFAlgorithm; enum { tls_prf_sha256 } PRFAlgorithm;
enum { null, rc4, 3des, aes } enum { null, rc4, 3des, aes }
BulkCipherAlgorithm; BulkCipherAlgorithm;
enum { stream, block, aead } CipherType; enum { stream, block, aead } CipherType;
enum { null, hmac_md5, hmac_sha1, hmac_sha256, enum { null, hmac_md5, hmac_sha1, hmac_sha256,
hmac_sha384, hmac_sha512} MACAlgorithm; hmac_sha384, hmac_sha512} MACAlgorithm;
enum { null(0), (255) } CompressionMethod; enum { null(0), (255) } CompressionMethod;
/* The algorithms specified in CompressionMethod, PRFAlgorithm /* The algorithms specified in CompressionMethod, PRFAlgorithm,
BulkCipherAlgorithm, and MACAlgorithm may be added to. */ BulkCipherAlgorithm, and MACAlgorithm may be added to. */
struct { struct {
ConnectionEnd entity; ConnectionEnd entity;
PRFAlgorithm prf_algorithm; PRFAlgorithm prf_algorithm;
BulkCipherAlgorithm bulk_cipher_algorithm; BulkCipherAlgorithm bulk_cipher_algorithm;
CipherType cipher_type; CipherType cipher_type;
uint8 enc_key_length; uint8 enc_key_length;
uint8 block_length; uint8 block_length;
uint8 fixed_iv_length; uint8 fixed_iv_length;
skipping to change at page 18, line 19 skipping to change at page 18, line 35
and are thus empty): and are thus empty):
client write MAC key client write MAC key
server write MAC key server write MAC key
client write encryption key client write encryption key
server write encryption key server write encryption key
client write IV client write IV
server write IV server write IV
The client write parameters are used by the server when receiving and The client write parameters are used by the server when receiving and
processing records and vice-versa. The algorithm used for generating processing records and vice versa. The algorithm used for generating
these items from the security parameters is described in Section 6.3. these items from the security parameters is described in Section 6.3.
Once the security parameters have been set and the keys have been Once the security parameters have been set and the keys have been
generated, the connection states can be instantiated by making them generated, the connection states can be instantiated by making them
the current states. These current states MUST be updated for each the current states. These current states MUST be updated for each
record processed. Each connection state includes the following record processed. Each connection state includes the following
elements: elements:
compression state compression state
The current state of the compression algorithm. The current state of the compression algorithm.
cipher state cipher state
The current state of the encryption algorithm. This will consist The current state of the encryption algorithm. This will consist
of the scheduled key for that connection. For stream ciphers, this of the scheduled key for that connection. For stream ciphers,
will also contain whatever state information is necessary to allow this will also contain whatever state information is necessary to
the stream to continue to encrypt or decrypt data. allow the stream to continue to encrypt or decrypt data.
MAC key MAC key
The MAC key for this connection, as generated above. The MAC key for this connection, as generated above.
sequence number sequence number
Each connection state contains a sequence number, which is Each connection state contains a sequence number, which is
maintained separately for read and write states. The sequence maintained separately for read and write states. The sequence
number MUST be set to zero whenever a connection state is made the number MUST be set to zero whenever a connection state is made the
active state. Sequence numbers are of type uint64 and may not active state. Sequence numbers are of type uint64 and may not
exceed 2^64-1. Sequence numbers do not wrap. If a TLS exceed 2^64-1. Sequence numbers do not wrap. If a TLS
implementation would need to wrap a sequence number, it must implementation would need to wrap a sequence number, it must
renegotiate instead. A sequence number is incremented after each renegotiate instead. A sequence number is incremented after each
record: specifically, the first record transmitted under a record: specifically, the first record transmitted under a
particular connection state MUST use sequence number 0. particular connection state MUST use sequence number 0.
6.2. Record layer 6.2. Record Layer
The TLS Record Layer receives uninterpreted data from higher layers
The TLS record layer receives uninterpreted data from higher layers
in non-empty blocks of arbitrary size. in non-empty blocks of arbitrary size.
6.2.1. Fragmentation 6.2.1. Fragmentation
The record layer fragments information blocks into TLSPlaintext The record layer fragments information blocks into TLSPlaintext
records carrying data in chunks of 2^14 bytes or less. Client message records carrying data in chunks of 2^14 bytes or less. Client
boundaries are not preserved in the record layer (i.e., multiple message boundaries are not preserved in the record layer (i.e.,
client messages of the same ContentType MAY be coalesced into a multiple client messages of the same ContentType MAY be coalesced
single TLSPlaintext record, or a single message MAY be fragmented into a single TLSPlaintext record, or a single message MAY be
across several records). fragmented across several records).
struct { struct {
uint8 major; uint8 major;
uint8 minor; uint8 minor;
} ProtocolVersion; } ProtocolVersion;
enum { enum {
change_cipher_spec(20), alert(21), handshake(22), change_cipher_spec(20), alert(21), handshake(22),
application_data(23), (255) application_data(23), (255)
} ContentType; } ContentType;
skipping to change at page 19, line 37 skipping to change at page 20, line 6
ContentType type; ContentType type;
ProtocolVersion version; ProtocolVersion version;
uint16 length; uint16 length;
opaque fragment[TLSPlaintext.length]; opaque fragment[TLSPlaintext.length];
} TLSPlaintext; } TLSPlaintext;
type type
The higher-level protocol used to process the enclosed fragment. The higher-level protocol used to process the enclosed fragment.
version version
The version of the protocol being employed. This document The version of the protocol being employed. This document
describes TLS Version 1.2, which uses the version { 3, 3 }. The describes TLS Version 1.2, which uses the version { 3, 3 }. The
version value 3.3 is historical, deriving from the use of {3, 1} version value 3.3 is historical, deriving from the use of {3, 1}
for TLS 1.0. (See Appendix A.1). Note that a client that supports for TLS 1.0. (See Appendix A.1.) Note that a client that
multiple versions of TLS may not know what version will be supports multiple versions of TLS may not know what version will
employed before it receives the ServerHello. See Appendix E for be employed before it receives the ServerHello. See Appendix E
discussion about what record layer version number should be for discussion about what record layer version number should be
employed for ClientHello. employed for ClientHello.
length length
The length (in bytes) of the following TLSPlaintext.fragment. The The length (in bytes) of the following TLSPlaintext.fragment. The
length MUST NOT exceed 2^14. length MUST NOT exceed 2^14.
fragment fragment
The application data. This data is transparent and treated as an The application data. This data is transparent and treated as an
independent block to be dealt with by the higher-level protocol independent block to be dealt with by the higher-level protocol
specified by the type field. specified by the type field.
Implementations MUST NOT send zero-length fragments of Handshake, Implementations MUST NOT send zero-length fragments of Handshake,
Alert, or ChangeCipherSpec content types. Zero-length fragments of Alert, or ChangeCipherSpec content types. Zero-length fragments of
Application data MAY be sent as they are potentially useful as a Application data MAY be sent as they are potentially useful as a
traffic analysis countermeasure. traffic analysis countermeasure.
Note: Data of different TLS Record layer content types MAY be Note: Data of different TLS record layer content types MAY be
interleaved. Application data is generally of lower precedence for interleaved. Application data is generally of lower precedence for
transmission than other content types. However, records MUST be transmission than other content types. However, records MUST be
delivered to the network in the same order as they are protected by delivered to the network in the same order as they are protected by
the record layer. Recipients MUST receive and process interleaved the record layer. Recipients MUST receive and process interleaved
application layer traffic during handshakes subsequent to the first application layer traffic during handshakes subsequent to the first
one on a connection. one on a connection.
6.2.2. Record Compression and Decompression 6.2.2. Record Compression and Decompression
All records are compressed using the compression algorithm defined in All records are compressed using the compression algorithm defined in
the current session state. There is always an active compression the current session state. There is always an active compression
algorithm; however, initially it is defined as algorithm; however, initially it is defined as
CompressionMethod.null. The compression algorithm translates a CompressionMethod.null. The compression algorithm translates a
TLSPlaintext structure into a TLSCompressed structure. Compression TLSPlaintext structure into a TLSCompressed structure. Compression
functions are initialized with default state information whenever a functions are initialized with default state information whenever a
connection state is made active. [RFC3749] describes compression connection state is made active. [RFC3749] describes compression
algorithms for TLS. algorithms for TLS.
Compression must be lossless and may not increase the content length Compression must be lossless and may not increase the content length
by more than 1024 bytes. If the decompression function encounters a by more than 1024 bytes. If the decompression function encounters a
TLSCompressed.fragment that would decompress to a length in excess of TLSCompressed.fragment that would decompress to a length in excess of
2^14 bytes, it MUST report a fatal decompression failure error. 2^14 bytes, it MUST report a fatal decompression failure error.
struct { struct {
ContentType type; /* same as TLSPlaintext.type */ ContentType type; /* same as TLSPlaintext.type */
ProtocolVersion version;/* same as TLSPlaintext.version */ ProtocolVersion version;/* same as TLSPlaintext.version */
uint16 length; uint16 length;
opaque fragment[TLSCompressed.length]; opaque fragment[TLSCompressed.length];
} TLSCompressed; } TLSCompressed;
length length
The length (in bytes) of the following TLSCompressed.fragment. The length (in bytes) of the following TLSCompressed.fragment.
The length MUST NOT exceed 2^14 + 1024. The length MUST NOT exceed 2^14 + 1024.
fragment fragment
The compressed form of TLSPlaintext.fragment. The compressed form of TLSPlaintext.fragment.
Note: A CompressionMethod.null operation is an identity operation; no Note: A CompressionMethod.null operation is an identity operation;
fields are altered. no fields are altered.
Implementation note: Decompression functions are responsible for Implementation note: Decompression functions are responsible for
ensuring that messages cannot cause internal buffer overflows. ensuring that messages cannot cause internal buffer overflows.
6.2.3. Record Payload Protection 6.2.3. Record Payload Protection
The encryption and MAC functions translate a TLSCompressed structure The encryption and MAC functions translate a TLSCompressed
into a TLSCiphertext. The decryption functions reverse the process. structure into a TLSCiphertext. The decryption functions reverse
The MAC of the record also includes a sequence number so that the process. The MAC of the record also includes a sequence
missing, extra, or repeated messages are detectable. number so that missing, extra, or repeated messages are
detectable.
struct { struct {
ContentType type; ContentType type;
ProtocolVersion version; ProtocolVersion version;
uint16 length; uint16 length;
select (SecurityParameters.cipher_type) { select (SecurityParameters.cipher_type) {
case stream: GenericStreamCipher; case stream: GenericStreamCipher;
case block: GenericBlockCipher; case block: GenericBlockCipher;
case aead: GenericAEADCipher; case aead: GenericAEADCipher;
} fragment; } fragment;
skipping to change at page 21, line 39 skipping to change at page 22, line 8
version version
The version field is identical to TLSCompressed.version. The version field is identical to TLSCompressed.version.
length length
The length (in bytes) of the following TLSCiphertext.fragment. The length (in bytes) of the following TLSCiphertext.fragment.
The length MUST NOT exceed 2^14 + 2048. The length MUST NOT exceed 2^14 + 2048.
fragment fragment
The encrypted form of TLSCompressed.fragment, with the MAC. The encrypted form of TLSCompressed.fragment, with the MAC.
6.2.3.1. Null or Standard Stream Cipher 6.2.3.1. Null or Standard Stream Cipher
Stream ciphers (including BulkCipherAlgorithm.null, see Appendix A.6) Stream ciphers (including BulkCipherAlgorithm.null; see Appendix A.6)
convert TLSCompressed.fragment structures to and from stream convert TLSCompressed.fragment structures to and from stream
TLSCiphertext.fragment structures. TLSCiphertext.fragment structures.
stream-ciphered struct { stream-ciphered struct {
opaque content[TLSCompressed.length]; opaque content[TLSCompressed.length];
opaque MAC[SecurityParameters.mac_length]; opaque MAC[SecurityParameters.mac_length];
} GenericStreamCipher; } GenericStreamCipher;
The MAC is generated as: The MAC is generated as:
skipping to change at page 22, line 17 skipping to change at page 22, line 35
TLSCompressed.fragment); TLSCompressed.fragment);
where "+" denotes concatenation. where "+" denotes concatenation.
seq_num seq_num
The sequence number for this record. The sequence number for this record.
MAC MAC
The MAC algorithm specified by SecurityParameters.mac_algorithm. The MAC algorithm specified by SecurityParameters.mac_algorithm.
Note that the MAC is computed before encryption. The stream cipher Note that the MAC is computed before encryption. The stream cipher
encrypts the entire block, including the MAC. For stream ciphers that encrypts the entire block, including the MAC. For stream ciphers
do not use a synchronization vector (such as RC4), the stream cipher that do not use a synchronization vector (such as RC4), the stream
state from the end of one record is simply used on the subsequent cipher state from the end of one record is simply used on the
packet. If the cipher suite is TLS_NULL_WITH_NULL_NULL, encryption subsequent packet. If the cipher suite is TLS_NULL_WITH_NULL_NULL,
consists of the identity operation (i.e., the data is not encrypted, encryption consists of the identity operation (i.e., the data is not
and the MAC size is zero, implying that no MAC is used). For both encrypted, and the MAC size is zero, implying that no MAC is used).
null and stream ciphers, TLSCiphertext.length is TLSCompressed.length For both null and stream ciphers, TLSCiphertext.length is
plus SecurityParameters.mac_length. TLSCompressed.length plus SecurityParameters.mac_length.
6.2.3.2. CBC Block Cipher 6.2.3.2. CBC Block Cipher
For block ciphers (such as 3DES, or AES), the encryption and MAC For block ciphers (such as 3DES or AES), the encryption and MAC
functions convert TLSCompressed.fragment structures to and from block functions convert TLSCompressed.fragment structures to and from block
TLSCiphertext.fragment structures. TLSCiphertext.fragment structures.
struct { struct {
opaque IV[SecurityParameters.record_iv_length]; opaque IV[SecurityParameters.record_iv_length];
block-ciphered struct { block-ciphered struct {
opaque content[TLSCompressed.length]; opaque content[TLSCompressed.length];
opaque MAC[SecurityParameters.mac_length]; opaque MAC[SecurityParameters.mac_length];
uint8 padding[GenericBlockCipher.padding_length]; uint8 padding[GenericBlockCipher.padding_length];
uint8 padding_length; uint8 padding_length;
}; };
} GenericBlockCipher; } GenericBlockCipher;
The MAC is generated as described in Section 6.2.3.1. The MAC is generated as described in Section 6.2.3.1.
IV IV
The Initialization Vector (IV) SHOULD be chosen at random, and The Initialization Vector (IV) SHOULD be chosen at random, and
MUST be unpredictable. Note that in versions of TLS prior to 1.1, MUST be unpredictable. Note that in versions of TLS prior to 1.1,
there was no IV field, and the last ciphertext block of the there was no IV field, and the last ciphertext block of the
previous record (the "CBC residue") was used as the IV. This was previous record (the "CBC residue") was used as the IV. This was
changed to prevent the attacks described in [CBCATT]. For block changed to prevent the attacks described in [CBCATT]. For block
ciphers, the IV length is of length ciphers, the IV length is of length
SecurityParameters.record_iv_length which is equal to the SecurityParameters.record_iv_length, which is equal to the
SecurityParameters.block_size. SecurityParameters.block_size.
padding padding
Padding that is added to force the length of the plaintext to be Padding that is added to force the length of the plaintext to be
an integral multiple of the block cipher's block length. The an integral multiple of the block cipher's block length. The
padding MAY be any length up to 255 bytes, as long as it results padding MAY be any length up to 255 bytes, as long as it results
in the TLSCiphertext.length being an integral multiple of the in the TLSCiphertext.length being an integral multiple of the
block length. Lengths longer than necessary might be desirable to block length. Lengths longer than necessary might be desirable to
frustrate attacks on a protocol that are based on analysis of the frustrate attacks on a protocol that are based on analysis of the
lengths of exchanged messages. Each uint8 in the padding data lengths of exchanged messages. Each uint8 in the padding data
vector MUST be filled with the padding length value. The receiver vector MUST be filled with the padding length value. The receiver
MUST check this padding and MUST use the bad_record_mac alert to MUST check this padding and MUST use the bad_record_mac alert to
indicate padding errors. indicate padding errors.
padding_length padding_length
The padding length MUST be such that the total size of the The padding length MUST be such that the total size of the
GenericBlockCipher structure is a multiple of the cipher's block GenericBlockCipher structure is a multiple of the cipher's block
length. Legal values range from zero to 255, inclusive. This length. Legal values range from zero to 255, inclusive. This
length specifies the length of the padding field exclusive of the length specifies the length of the padding field exclusive of the
padding_length field itself. padding_length field itself.
The encrypted data length (TLSCiphertext.length) is one more than the The encrypted data length (TLSCiphertext.length) is one more than the
sum of SecurityParameters.block_length, TLSCompressed.length, sum of SecurityParameters.block_length, TLSCompressed.length,
SecurityParameters.mac_length, and padding_length. SecurityParameters.mac_length, and padding_length.
Example: If the block length is 8 bytes, the content length Example: If the block length is 8 bytes, the content length
(TLSCompressed.length) is 61 bytes, and the MAC length is 20 bytes, (TLSCompressed.length) is 61 bytes, and the MAC length is 20 bytes,
then the length before padding is 82 bytes (this does not include the then the length before padding is 82 bytes (this does not include the
IV. Thus, the padding length modulo 8 must be equal to 6 in order to IV. Thus, the padding length modulo 8 must be equal to 6 in order to
make the total length an even multiple of 8 bytes (the block length). make the total length an even multiple of 8 bytes (the block length).
The padding length can be 6, 14, 22, and so on, through 254. If the The padding length can be 6, 14, 22, and so on, through 254. If the
padding length were the minimum necessary, 6, the padding would be 6 padding length were the minimum necessary, 6, the padding would be 6
bytes, each containing the value 6. Thus, the last 8 octets of the bytes, each containing the value 6. Thus, the last 8 octets of the
GenericBlockCipher before block encryption would be xx 06 06 06 06 06 GenericBlockCipher before block encryption would be xx 06 06 06 06 06
06 06, where xx is the last octet of the MAC. 06 06, where xx is the last octet of the MAC.
Note: With block ciphers in CBC mode (Cipher Block Chaining), it is Note: With block ciphers in CBC mode (Cipher Block Chaining), it is
critical that the entire plaintext of the record be known before any critical that the entire plaintext of the record be known before any
ciphertext is transmitted. Otherwise, it is possible for the attacker ciphertext is transmitted. Otherwise, it is possible for the
to mount the attack described in [CBCATT]. attacker to mount the attack described in [CBCATT].
Implementation Note: Canvel et al. [CBCTIME] have demonstrated a Implementation note: Canvel et al. [CBCTIME] have demonstrated a
timing attack on CBC padding based on the time required to compute timing attack on CBC padding based on the time required to compute
the MAC. In order to defend against this attack, implementations MUST the MAC. In order to defend against this attack, implementations
ensure that record processing time is essentially the same whether or MUST ensure that record processing time is essentially the same
not the padding is correct. In general, the best way to do this is whether or not the padding is correct. In general, the best way to
to compute the MAC even if the padding is incorrect, and only then do this is to compute the MAC even if the padding is incorrect, and
reject the packet. For instance, if the pad appears to be incorrect, only then reject the packet. For instance, if the pad appears to be
the implementation might assume a zero-length pad and then compute incorrect, the implementation might assume a zero-length pad and then
the MAC. This leaves a small timing channel, since MAC performance compute the MAC. This leaves a small timing channel, since MAC
depends to some extent on the size of the data fragment, but it is performance depends to some extent on the size of the data fragment,
not believed to be large enough to be exploitable, due to the large but it is not believed to be large enough to be exploitable, due to
block size of existing MACs and the small size of the timing signal. the large block size of existing MACs and the small size of the
timing signal.
6.2.3.3. AEAD ciphers 6.2.3.3. AEAD Ciphers
For AEAD [AEAD] ciphers (such as [CCM] or [GCM]) the AEAD function For AEAD [AEAD] ciphers (such as [CCM] or [GCM]), the AEAD function
converts TLSCompressed.fragment structures to and from AEAD converts TLSCompressed.fragment structures to and from AEAD
TLSCiphertext.fragment structures. TLSCiphertext.fragment structures.
struct { struct {
opaque nonce_explicit[SecurityParameters.record_iv_length]; opaque nonce_explicit[SecurityParameters.record_iv_length];
aead-ciphered struct { aead-ciphered struct {
opaque content[TLSCompressed.length]; opaque content[TLSCompressed.length];
}; };
} GenericAEADCipher; } GenericAEADCipher;
AEAD ciphers take as input a single key, a nonce, a plaintext, and AEAD ciphers take as input a single key, a nonce, a plaintext, and
"additional data" to be included in the authentication check, as "additional data" to be included in the authentication check, as
described in Section 2.1 of [AEAD]. The key is either the described in Section 2.1 of [AEAD]. The key is either the
client_write_key or the server_write_key. No MAC key is used. client_write_key or the server_write_key. No MAC key is used.
Each AEAD cipher suite MUST specify how the nonce supplied to the Each AEAD cipher suite MUST specify how the nonce supplied to the
AEAD operation is constructed, and what is the length of the AEAD operation is constructed, and what is the length of the
GenericAEADCipher.nonce_explicit part. In many cases, it is GenericAEADCipher.nonce_explicit part. In many cases, it is
appropriate to use the partially implicit nonce technique described appropriate to use the partially implicit nonce technique described
in Section 3.2.1 of [AEAD]; with record_iv_length being the length of in Section 3.2.1 of [AEAD]; with record_iv_length being the length of
the explicit part. In this case, the implicit part SHOULD be derived the explicit part. In this case, the implicit part SHOULD be derived
from key_block as client_write_iv and server_write_iv (as described from key_block as client_write_iv and server_write_iv (as described
in Section 6.3), and the explicit part is included in in Section 6.3), and the explicit part is included in
GenericAEAEDCipher.nonce_explicit. GenericAEAEDCipher.nonce_explicit.
The plaintext is the TLSCompressed.fragment. The plaintext is the TLSCompressed.fragment.
The additional authenticated data, which we denote as The additional authenticated data, which we denote as
additional_data, is defined as follows: additional_data, is defined as follows:
additional_data = seq_num + TLSCompressed.type + additional_data = seq_num + TLSCompressed.type +
TLSCompressed.version + TLSCompressed.length; TLSCompressed.version + TLSCompressed.length;
Where "+" denotes concatenation. where "+" denotes concatenation.
The aead_output consists of the ciphertext output by the AEAD The aead_output consists of the ciphertext output by the AEAD
encryption operation. The length will generally be larger than encryption operation. The length will generally be larger than
TLSCompressed.length, but by an amount that varies with the AEAD TLSCompressed.length, but by an amount that varies with the AEAD
cipher. Since the ciphers might incorporate padding, the amount of cipher. Since the ciphers might incorporate padding, the amount of
overhead could vary with different TLSCompressed.length values. Each overhead could vary with different TLSCompressed.length values. Each
AEAD cipher MUST NOT produce an expansion of greater than 1024 bytes. AEAD cipher MUST NOT produce an expansion of greater than 1024 bytes.
Symbolically, Symbolically,
AEADEncrypted = AEAD-Encrypt(key, nonce, plaintext, AEADEncrypted = AEAD-Encrypt(write_key, nonce, plaintext,
additional_data) additional_data)
In order to decrypt and verify, the cipher takes as input the key, In order to decrypt and verify, the cipher takes as input the key,
nonce, the "additional_data", and the AEADEncrypted value. The output nonce, the "additional_data", and the AEADEncrypted value. The
is either the plaintext or an error indicating that the decryption output is either the plaintext or an error indicating that the
failed. There is no separate integrity check. I.e., decryption failed. There is no separate integrity check. That is:
TLSCompressed.fragment = AEAD-Decrypt(write_key, nonce, TLSCompressed.fragment = AEAD-Decrypt(write_key, nonce,
AEADEncrypted, AEADEncrypted,
additional_data) additional_data)
If the decryption fails, a fatal bad_record_mac alert MUST be If the decryption fails, a fatal bad_record_mac alert MUST be
generated. generated.
6.3. Key Calculation 6.3. Key Calculation
The Record Protocol requires an algorithm to generate keys required The Record Protocol requires an algorithm to generate keys required
by the current connection state (see Appendix A.6) from the security by the current connection state (see Appendix A.6) from the security
parameters provided by the handshake protocol. parameters provided by the handshake protocol.
The master secret is expanded into a sequence of secure bytes, which The master secret is expanded into a sequence of secure bytes, which
is then split to a client write MAC key, a server write MAC key, a is then split to a client write MAC key, a server write MAC key, a
client write encryption key, and a server write encryption key. Each client write encryption key, and a server write encryption key. Each
of these is generated from the byte sequence in that order. Unused of these is generated from the byte sequence in that order. Unused
values are empty. Some AEAD ciphers may additionally require a values are empty. Some AEAD ciphers may additionally require a
client write IV and a server write IV (see Section 6.2.3.3). client write IV and a server write IV (see Section 6.2.3.3).
When keys and MAC keys are generated, the master secret is used as an When keys and MAC keys are generated, the master secret is used as an
entropy source. entropy source.
To generate the key material, compute To generate the key material, compute
key_block = PRF(SecurityParameters.master_secret, key_block = PRF(SecurityParameters.master_secret,
"key expansion", "key expansion",
SecurityParameters.server_random + SecurityParameters.server_random +
SecurityParameters.client_random); SecurityParameters.client_random);
until enough output has been generated. Then the key_block is until enough output has been generated. Then, the key_block is
partitioned as follows: partitioned as follows:
client_write_MAC_key[SecurityParameters.mac_key_length] client_write_MAC_key[SecurityParameters.mac_key_length]
server_write_MAC_key[SecurityParameters.mac_key_length] server_write_MAC_key[SecurityParameters.mac_key_length]
client_write_key[SecurityParameters.enc_key_length] client_write_key[SecurityParameters.enc_key_length]
server_write_key[SecurityParameters.enc_key_length] server_write_key[SecurityParameters.enc_key_length]
client_write_IV[SecurityParameters.fixed_iv_length] client_write_IV[SecurityParameters.fixed_iv_length]
server_write_IV[SecurityParameters.fixed_iv_length] server_write_IV[SecurityParameters.fixed_iv_length]
Currently, the client_write_IV and server_write_IV are only generated Currently, the client_write_IV and server_write_IV are only generated
for implicit nonce techniques as described in Section 3.2.1 of for implicit nonce techniques as described in Section 3.2.1 of
[AEAD]. [AEAD].
Implementation note: The currently defined cipher suite which Implementation note: The currently defined cipher suite which
requires the most material is AES_256_CBC_SHA256. It requires 2 x 32 requires the most material is AES_256_CBC_SHA256. It requires 2 x 32
byte keys and 2 x 32 byte MAC keys, for a total 128 bytes of key byte keys and 2 x 32 byte MAC keys, for a total 128 bytes of key
material. material.
7. The TLS Handshaking Protocols 7. The TLS Handshaking Protocols
TLS has three subprotocols that are used to allow peers to agree upon TLS has three subprotocols that are used to allow peers to agree upon
security parameters for the record layer, to authenticate themselves, security parameters for the record layer, to authenticate themselves,
to instantiate negotiated security parameters, and to report error to instantiate negotiated security parameters, and to report error
conditions to each other. conditions to each other.
The Handshake Protocol is responsible for negotiating a session, The Handshake Protocol is responsible for negotiating a session,
which consists of the following items: which consists of the following items:
session identifier session identifier
An arbitrary byte sequence chosen by the server to identify an An arbitrary byte sequence chosen by the server to identify an
active or resumable session state. active or resumable session state.
peer certificate peer certificate
X509v3 [PKIX] certificate of the peer. This element of the state X509v3 [PKIX] certificate of the peer. This element of the state
may be null. may be null.
compression method compression method
The algorithm used to compress data prior to encryption. The algorithm used to compress data prior to encryption.
cipher spec cipher spec
Specifies the pseudorandom function (PRF) used to generate keying Specifies the pseudorandom function (PRF) used to generate keying
material, the bulk data encryption algorithm (such as null, AES, material, the bulk data encryption algorithm (such as null, AES,
etc.) and a MAC algorithm (such as HMAC-SHA1). It also defines etc.) and the MAC algorithm (such as HMAC-SHA1). It also defines
cryptographic attributes such as the mac_length. (See Appendix A.6 cryptographic attributes such as the mac_length. (See Appendix
for formal definition.) A.6 for formal definition.)
master secret master secret
48-byte secret shared between the client and server. 48-byte secret shared between the client and server.
is resumable is resumable
A flag indicating whether the session can be used to initiate new A flag indicating whether the session can be used to initiate new
connections. connections.
These items are then used to create security parameters for use by These items are then used to create security parameters for use by
the Record Layer when protecting application data. Many connections the record layer when protecting application data. Many connections
can be instantiated using the same session through the resumption can be instantiated using the same session through the resumption
feature of the TLS Handshake Protocol. feature of the TLS Handshake Protocol.
7.1. Change Cipher Spec Protocol 7.1. Change Cipher Spec Protocol
The change cipher spec protocol exists to signal transitions in The change cipher spec protocol exists to signal transitions in
ciphering strategies. The protocol consists of a single message, ciphering strategies. The protocol consists of a single message,
which is encrypted and compressed under the current (not the pending) which is encrypted and compressed under the current (not the pending)
connection state. The message consists of a single byte of value 1. connection state. The message consists of a single byte of value 1.
struct { struct {
enum { change_cipher_spec(1), (255) } type; enum { change_cipher_spec(1), (255) } type;
} ChangeCipherSpec; } ChangeCipherSpec;
The ChangeCipherSpec message is sent by both the client and the The ChangeCipherSpec message is sent by both the client and the
server to notify the receiving party that subsequent records will be server to notify the receiving party that subsequent records will be
protected under the newly negotiated CipherSpec and keys. Reception protected under the newly negotiated CipherSpec and keys. Reception
of this message causes the receiver to instruct the Record Layer to of this message causes the receiver to instruct the record layer to
immediately copy the read pending state into the read current state. immediately copy the read pending state into the read current state.
Immediately after sending this message, the sender MUST instruct the Immediately after sending this message, the sender MUST instruct the
record layer to make the write pending state the write active state. record layer to make the write pending state the write active state.
(See Section 6.1.) The change cipher spec message is sent during the
(See Section 6.1.) The ChangeCipherSpec message is sent during the
handshake after the security parameters have been agreed upon, but handshake after the security parameters have been agreed upon, but
before the verifying finished message is sent. before the verifying Finished message is sent.
Note: If a rehandshake occurs while data is flowing on a connection, Note: If a rehandshake occurs while data is flowing on a connection,
the communicating parties may continue to send data using the old the communicating parties may continue to send data using the old
CipherSpec. However, once the ChangeCipherSpec has been sent, the new CipherSpec. However, once the ChangeCipherSpec has been sent, the
CipherSpec MUST be used. The first side to send the ChangeCipherSpec new CipherSpec MUST be used. The first side to send the
does not know that the other side has finished computing the new ChangeCipherSpec does not know that the other side has finished
keying material (e.g., if it has to perform a time consuming public computing the new keying material (e.g., if it has to perform a
key operation). Thus, a small window of time, during which the time-consuming public key operation). Thus, a small window of time,
recipient must buffer the data, MAY exist. In practice, with modern during which the recipient must buffer the data, MAY exist. In
machines this interval is likely to be fairly short. practice, with modern machines this interval is likely to be fairly
short.
7.2. Alert Protocol 7.2. Alert Protocol
One of the content types supported by the TLS Record layer is the One of the content types supported by the TLS record layer is the
alert type. Alert messages convey the severity of the message alert type. Alert messages convey the severity of the message
(warning or fatal) and a description of the alert. Alert messages (warning or fatal) and a description of the alert. Alert messages
with a level of fatal result in the immediate termination of the with a level of fatal result in the immediate termination of the
connection. In this case, other connections corresponding to the connection. In this case, other connections corresponding to the
session may continue, but the session identifier MUST be invalidated, session may continue, but the session identifier MUST be invalidated,
preventing the failed session from being used to establish new preventing the failed session from being used to establish new
connections. Like other messages, alert messages are encrypted and connections. Like other messages, alert messages are encrypted and
compressed, as specified by the current connection state. compressed, as specified by the current connection state.
enum { warning(1), fatal(2), (255) } AlertLevel; enum { warning(1), fatal(2), (255) } AlertLevel;
enum { enum {
close_notify(0), close_notify(0),
unexpected_message(10), unexpected_message(10),
bad_record_mac(20), bad_record_mac(20),
decryption_failed_RESERVED(21), decryption_failed_RESERVED(21),
record_overflow(22), record_overflow(22),
skipping to change at page 28, line 43 skipping to change at page 29, line 19
no_renegotiation(100), no_renegotiation(100),
unsupported_extension(110), unsupported_extension(110),
(255) (255)
} AlertDescription; } AlertDescription;
struct { struct {
AlertLevel level; AlertLevel level;
AlertDescription description; AlertDescription description;
} Alert; } Alert;
7.2.1. Closure Alerts 7.2.1. Closure Alerts
The client and the server must share knowledge that the connection is The client and the server must share knowledge that the connection is
ending in order to avoid a truncation attack. Either party may ending in order to avoid a truncation attack. Either party may
initiate the exchange of closing messages. initiate the exchange of closing messages.
close_notify close_notify
This message notifies the recipient that the sender will not send This message notifies the recipient that the sender will not send
any more messages on this connection. Note that as of TLS 1.1, any more messages on this connection. Note that as of TLS 1.1,
failure to properly close a connection no longer requires that a failure to properly close a connection no longer requires that a
session not be resumed. This is a change from TLS 1.0 to conform session not be resumed. This is a change from TLS 1.0 to conform
with widespread implementation practice. with widespread implementation practice.
Either party may initiate a close by sending a close_notify alert. Either party may initiate a close by sending a close_notify alert.
Any data received after a closure alert is ignored. Any data received after a closure alert is ignored.
Unless some other fatal alert has been transmitted, each party is Unless some other fatal alert has been transmitted, each party is
required to send a close_notify alert before closing the write side required to send a close_notify alert before closing the write side
of the connection. The other party MUST respond with a close_notify of the connection. The other party MUST respond with a close_notify
alert of its own and close down the connection immediately, alert of its own and close down the connection immediately,
discarding any pending writes. It is not required for the initiator discarding any pending writes. It is not required for the initiator
of the close to wait for the responding close_notify alert before of the close to wait for the responding close_notify alert before
closing the read side of the connection. closing the read side of the connection.
If the application protocol using TLS provides that any data may be If the application protocol using TLS provides that any data may be
carried over the underlying transport after the TLS connection is carried over the underlying transport after the TLS connection is
closed, the TLS implementation must receive the responding closed, the TLS implementation must receive the responding
close_notify alert before indicating to the application layer that close_notify alert before indicating to the application layer that
the TLS connection has ended. If the application protocol will not the TLS connection has ended. If the application protocol will not
transfer any additional data, but will only close the underlying transfer any additional data, but will only close the underlying
transport connection, then the implementation MAY choose to close the transport connection, then the implementation MAY choose to close the
transport without waiting for the responding close_notify. No part of transport without waiting for the responding close_notify. No part
this standard should be taken to dictate the manner in which a usage of this standard should be taken to dictate the manner in which a
profile for TLS manages its data transport, including when usage profile for TLS manages its data transport, including when
connections are opened or closed. connections are opened or closed.
Note: It is assumed that closing a connection reliably delivers Note: It is assumed that closing a connection reliably delivers
pending data before destroying the transport. pending data before destroying the transport.
7.2.2. Error Alerts 7.2.2. Error Alerts
Error handling in the TLS Handshake protocol is very simple. When an Error handling in the TLS Handshake protocol is very simple. When an
error is detected, the detecting party sends a message to the other error is detected, the detecting party sends a message to the other
party. Upon transmission or receipt of a fatal alert message, both party. Upon transmission or receipt of a fatal alert message, both
parties immediately close the connection. Servers and clients MUST parties immediately close the connection. Servers and clients MUST
forget any session-identifiers, keys, and secrets associated with a forget any session-identifiers, keys, and secrets associated with a
failed connection. Thus, any connection terminated with a fatal alert failed connection. Thus, any connection terminated with a fatal
MUST NOT be resumed. alert MUST NOT be resumed.
Whenever an implementation encounters a condition which is defined as Whenever an implementation encounters a condition which is defined as
a fatal alert, it MUST send the appropriate alert prior to closing a fatal alert, it MUST send the appropriate alert prior to closing
the connection. For all errors where an alert level is not explicitly the connection. For all errors where an alert level is not
specified, the sending party MAY determine at its discretion whether explicitly specified, the sending party MAY determine at its
to treat this as a fatal error or not. If the implementation chooses discretion whether to treat this as a fatal error or not. If the
to send an alert but intends to close the connection immediately implementation chooses to send an alert but intends to close the
afterwards, it MUST send that alert at the fatal alert level. connection immediately afterwards, it MUST send that alert at the
fatal alert level.
If an alert with a level of warning is sent and received, generally If an alert with a level of warning is sent and received, generally
the connection can continue normally. If the receiving party decides the connection can continue normally. If the receiving party decides
not to proceed with the connection (e.g., after having received a not to proceed with the connection (e.g., after having received a
no_renegotiation alert that it is not willing to accept), it SHOULD no_renegotiation alert that it is not willing to accept), it SHOULD
send a fatal alert to terminate the connection. Given this, the send a fatal alert to terminate the connection. Given this, the
sending party cannot, in general, know how the receiving party will sending party cannot, in general, know how the receiving party will
behave. Therefore, warning alerts are not very useful when the behave. Therefore, warning alerts are not very useful when the
sending party wants to continue the connection, and thus are sending party wants to continue the connection, and thus are
sometimes omitted. For example, if a peer decides to accept an sometimes omitted. For example, if a peer decides to accept an
expired certificate (perhaps after confirming this with the user) and expired certificate (perhaps after confirming this with the user) and
wants to continue the connection, it would not generally send a wants to continue the connection, it would not generally send a
certificate_expired alert. certificate_expired alert.
The following error alerts are defined: The following error alerts are defined:
unexpected_message unexpected_message
An inappropriate message was received. This alert is always fatal An inappropriate message was received. This alert is always fatal
and should never be observed in communication between proper and should never be observed in communication between proper
implementations. implementations.
bad_record_mac bad_record_mac
This alert is returned if a record is received with an incorrect This alert is returned if a record is received with an incorrect
MAC. This alert also MUST be returned if an alert is sent because MAC. This alert also MUST be returned if an alert is sent because
a TLSCiphertext decrypted in an invalid way: either it wasn't an a TLSCiphertext decrypted in an invalid way: either it wasn't an
even multiple of the block length, or its padding values, when even multiple of the block length, or its padding values, when
checked, weren't correct. This message is always fatal and should checked, weren't correct. This message is always fatal and should
never be observed in communication between proper implementations never be observed in communication between proper implementations
(except when messages were corrupted in the network). (except when messages were corrupted in the network).
decryption_failed_RESERVED decryption_failed_RESERVED
This alert was used in some earlier versions of TLS, and may have This alert was used in some earlier versions of TLS, and may have
permitted certain attacks against the CBC mode [CBCATT]. It MUST permitted certain attacks against the CBC mode [CBCATT]. It MUST
NOT be sent by compliant implementations. NOT be sent by compliant implementations.
record_overflow record_overflow
A TLSCiphertext record was received that had a length more than A TLSCiphertext record was received that had a length more than
2^14+2048 bytes, or a record decrypted to a TLSCompressed record 2^14+2048 bytes, or a record decrypted to a TLSCompressed record
with more than 2^14+1024 bytes. This message is always fatal and with more than 2^14+1024 bytes. This message is always fatal and
should never be observed in communication between proper should never be observed in communication between proper
implementations (except when messages were corrupted in the implementations (except when messages were corrupted in the
network). network).
decompression_failure decompression_failure
The decompression function received improper input (e.g., data The decompression function received improper input (e.g., data
that would expand to excessive length). This message is always that would expand to excessive length). This message is always
fatal and should never be observed in communication between proper fatal and should never be observed in communication between proper
implementations. implementations.
handshake_failure handshake_failure
Reception of a handshake_failure alert message indicates that the Reception of a handshake_failure alert message indicates that the
sender was unable to negotiate an acceptable set of security sender was unable to negotiate an acceptable set of security
parameters given the options available. This is a fatal error. parameters given the options available. This is a fatal error.
no_certificate_RESERVED no_certificate_RESERVED
This alert was used in SSLv3 but not any version of TLS. It MUST This alert was used in SSLv3 but not any version of TLS. It MUST
NOT be sent by compliant implementations. NOT be sent by compliant implementations.
bad_certificate bad_certificate
A certificate was corrupt, contained signatures that did not A certificate was corrupt, contained signatures that did not
verify correctly, etc. verify correctly, etc.
unsupported_certificate unsupported_certificate
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certificate_expired certificate_expired
A certificate has expired or is not currently valid. A certificate has expired or is not currently valid.
certificate_unknown certificate_unknown
Some other (unspecified) issue arose in processing the Some other (unspecified) issue arose in processing the
certificate, rendering it unacceptable. certificate, rendering it unacceptable.
illegal_parameter illegal_parameter
A field in the handshake was out of range or inconsistent with A field in the handshake was out of range or inconsistent with
other fields. This message is always fatal. other fields. This message is always fatal.
unknown_ca unknown_ca
A valid certificate chain or partial chain was received, but the A valid certificate chain or partial chain was received, but the
certificate was not accepted because the CA certificate could not certificate was not accepted because the CA certificate could not
be located or couldn't be matched with a known, trusted CA. This be located or couldn't be matched with a known, trusted CA. This
message is always fatal. message is always fatal.
access_denied access_denied
A valid certificate was received, but when access control was A valid certificate was received, but when access control was
applied, the sender decided not to proceed with negotiation. This applied, the sender decided not to proceed with negotiation. This
message is always fatal. message is always fatal.
decode_error decode_error
A message could not be decoded because some field was out of the A message could not be decoded because some field was out of the
specified range or the length of the message was incorrect. This specified range or the length of the message was incorrect. This
message is always fatal and should never be observed in message is always fatal and should never be observed in
communication between proper implementations (except when messages communication between proper implementations (except when messages
were corrupted in the network). were corrupted in the network).
decrypt_error decrypt_error
A handshake cryptographic operation failed, including being unable A handshake cryptographic operation failed, including being unable
to correctly verify a signature or validate a finished message. to correctly verify a signature or validate a Finished message.
This message is always fatal. This message is always fatal.
export_restriction_RESERVED export_restriction_RESERVED
This alert was used in some earlier versions of TLS. It MUST NOT This alert was used in some earlier versions of TLS. It MUST NOT
be sent by compliant implementations. be sent by compliant implementations.
protocol_version protocol_version
The protocol version the client has attempted to negotiate is The protocol version the client has attempted to negotiate is
recognized but not supported. (For example, old protocol versions recognized but not supported. (For example, old protocol versions
might be avoided for security reasons). This message is always might be avoided for security reasons.) This message is always
fatal. fatal.
insufficient_security insufficient_security
Returned instead of handshake_failure when a negotiation has Returned instead of handshake_failure when a negotiation has
failed specifically because the server requires ciphers more failed specifically because the server requires ciphers more
secure than those supported by the client. This message is always secure than those supported by the client. This message is always
fatal. fatal.
internal_error internal_error
An internal error unrelated to the peer or the correctness of the An internal error unrelated to the peer or the correctness of the
protocol (such as a memory allocation failure) makes it impossible protocol (such as a memory allocation failure) makes it impossible
to continue. This message is always fatal. to continue. This message is always fatal.
user_canceled user_canceled
This handshake is being canceled for some reason unrelated to a This handshake is being canceled for some reason unrelated to a
protocol failure. If the user cancels an operation after the protocol failure. If the user cancels an operation after the
handshake is complete, just closing the connection by sending a handshake is complete, just closing the connection by sending a
close_notify is more appropriate. This alert should be followed by close_notify is more appropriate. This alert should be followed
a close_notify. This message is generally a warning. by a close_notify. This message is generally a warning.
no_renegotiation no_renegotiation
Sent by the client in response to a hello request or by the server Sent by the client in response to a hello request or by the server
in response to a client hello after initial handshaking. Either in response to a client hello after initial handshaking. Either
of these would normally lead to renegotiation; when that is not of these would normally lead to renegotiation; when that is not
appropriate, the recipient should respond with this alert. At appropriate, the recipient should respond with this alert. At
that point, the original requester can decide whether to proceed that point, the original requester can decide whether to proceed
with the connection. One case where this would be appropriate is with the connection. One case where this would be appropriate is
where a server has spawned a process to satisfy a request; the where a server has spawned a process to satisfy a request; the
process might receive security parameters (key length, process might receive security parameters (key length,
authentication, etc.) at startup and it might be difficult to authentication, etc.) at startup, and it might be difficult to
communicate changes to these parameters after that point. This communicate changes to these parameters after that point. This
message is always a warning. message is always a warning.
unsupported_extension unsupported_extension
sent by clients that receive an extended server hello containing sent by clients that receive an extended server hello containing
an extension that they did not put in the corresponding client an extension that they did not put in the corresponding client
hello. This message is always fatal. hello. This message is always fatal.
New Alert values are assigned by IANA as described in Section 12. New Alert values are assigned by IANA as described in Section 12.
7.3. Handshake Protocol Overview 7.3. Handshake Protocol Overview
The cryptographic parameters of the session state are produced by the The cryptographic parameters of the session state are produced by the
TLS Handshake Protocol, which operates on top of the TLS Record TLS Handshake Protocol, which operates on top of the TLS record
Layer. When a TLS client and server first start communicating, they layer. When a TLS client and server first start communicating, they
agree on a protocol version, select cryptographic algorithms, agree on a protocol version, select cryptographic algorithms,
optionally authenticate each other, and use public-key encryption optionally authenticate each other, and use public-key encryption
techniques to generate shared secrets. techniques to generate shared secrets.
The TLS Handshake Protocol involves the following steps: The TLS Handshake Protocol involves the following steps:
- Exchange hello messages to agree on algorithms, exchange random - Exchange hello messages to agree on algorithms, exchange random
values, and check for session resumption. values, and check for session resumption.
- Exchange the necessary cryptographic parameters to allow the - Exchange the necessary cryptographic parameters to allow the
skipping to change at page 33, line 40 skipping to change at page 34, line 27
random values. random values.
- Provide security parameters to the record layer. - Provide security parameters to the record layer.
- Allow the client and server to verify that their peer has - Allow the client and server to verify that their peer has
calculated the same security parameters and that the handshake calculated the same security parameters and that the handshake
occurred without tampering by an attacker. occurred without tampering by an attacker.
Note that higher layers should not be overly reliant on whether TLS Note that higher layers should not be overly reliant on whether TLS
always negotiates the strongest possible connection between two always negotiates the strongest possible connection between two
peers. There are a number of ways in which a man in the middle peers. There are a number of ways in which a man-in-the-middle
attacker can attempt to make two entities drop down to the least attacker can attempt to make two entities drop down to the least
secure method they support. The protocol has been designed to secure method they support. The protocol has been designed to
minimize this risk, but there are still attacks available: for minimize this risk, but there are still attacks available: for
example, an attacker could block access to the port a secure service example, an attacker could block access to the port a secure service
runs on, or attempt to get the peers to negotiate an unauthenticated runs on, or attempt to get the peers to negotiate an unauthenticated
connection. The fundamental rule is that higher levels must be connection. The fundamental rule is that higher levels must be
cognizant of what their security requirements are and never transmit cognizant of what their security requirements are and never transmit
information over a channel less secure than what they require. The information over a channel less secure than what they require. The
TLS protocol is secure in that any cipher suite offers its promised TLS protocol is secure in that any cipher suite offers its promised
level of security: if you negotiate 3DES with a 1024 bit RSA key level of security: if you negotiate 3DES with a 1024-bit RSA key
exchange with a host whose certificate you have verified, you can exchange with a host whose certificate you have verified, you can
expect to be that secure. expect to be that secure.
These goals are achieved by the handshake protocol, which can be These goals are achieved by the handshake protocol, which can be
summarized as follows: The client sends a client hello message to summarized as follows: The client sends a ClientHello message to
which the server must respond with a server hello message, or else a which the server must respond with a ServerHello message, or else a
fatal error will occur and the connection will fail. The client hello fatal error will occur and the connection will fail. The ClientHello
and server hello are used to establish security enhancement and ServerHello are used to establish security enhancement
capabilities between client and server. The client hello and server capabilities between client and server. The ClientHello and
hello establish the following attributes: Protocol Version, Session ServerHello establish the following attributes: Protocol Version,
ID, Cipher Suite, and Compression Method. Additionally, two random Session ID, Cipher Suite, and Compression Method. Additionally, two
values are generated and exchanged: ClientHello.random and random values are generated and exchanged: ClientHello.random and
ServerHello.random. ServerHello.random.
The actual key exchange uses up to four messages: the server The actual key exchange uses up to four messages: the server
Certificate, the ServerKeyExchange, the client Certificate, and the Certificate, the ServerKeyExchange, the client Certificate, and the
ClientKeyExchange. New key exchange methods can be created by ClientKeyExchange. New key exchange methods can be created by
specifying a format for these messages and by defining the use of the specifying a format for these messages and by defining the use of the
messages to allow the client and server to agree upon a shared messages to allow the client and server to agree upon a shared
secret. This secret MUST be quite long; currently defined key secret. This secret MUST be quite long; currently defined key
exchange methods exchange secrets that range from 46 bytes upwards. exchange methods exchange secrets that range from 46 bytes upwards.
Following the hello messages, the server will send its certificate in Following the hello messages, the server will send its certificate in
a Certificate message if it is to be authenticated. Additionally, a a Certificate message if it is to be authenticated. Additionally, a
ServerKeyExchange message may be sent, if it is required (e.g., if ServerKeyExchange message may be sent, if it is required (e.g., if
the server has no certificate, or if its certificate is for signing the server has no certificate, or if its certificate is for signing
only). If the server is authenticated, it may request a certificate only). If the server is authenticated, it may request a certificate
from the client, if that is appropriate to the cipher suite selected. from the client, if that is appropriate to the cipher suite selected.
Next, the server will send the ServerHelloDone message, indicating Next, the server will send the ServerHelloDone message, indicating
that the hello-message phase of the handshake is complete. The server that the hello-message phase of the handshake is complete. The
will then wait for a client response. If the server has sent a server will then wait for a client response. If the server has sent
CertificateRequest message, the client MUST send the Certificate a CertificateRequest message, the client MUST send the Certificate
message. The ClientKeyExchange message is now sent, and the content message. The ClientKeyExchange message is now sent, and the content
of that message will depend on the public key algorithm selected of that message will depend on the public key algorithm selected
between the client hello and the server hello. If the client has sent between the ClientHello and the ServerHello. If the client has sent
a certificate with signing ability, a digitally-signed a certificate with signing ability, a digitally-signed
CertificateVerify message is sent to explicitly verify possession of CertificateVerify message is sent to explicitly verify possession of
the private key in the certificate. the private key in the certificate.
At this point, a ChangeCipherSpec message is sent by the client, and At this point, a ChangeCipherSpec message is sent by the client, and
the client copies the pending Cipher Spec into the current Cipher the client copies the pending Cipher Spec into the current Cipher
Spec. The client then immediately sends the Finished message under Spec. The client then immediately sends the Finished message under
the new algorithms, keys, and secrets. In response, the server will the new algorithms, keys, and secrets. In response, the server will
send its own ChangeCipherSpec message, transfer the pending to the send its own ChangeCipherSpec message, transfer the pending to the
current Cipher Spec, and send its Finished message under the new current Cipher Spec, and send its Finished message under the new
Cipher Spec. At this point, the handshake is complete, and the client Cipher Spec. At this point, the handshake is complete, and the
and server may begin to exchange application layer data. (See flow client and server may begin to exchange application layer data. (See
chart below.) Application data MUST NOT be sent prior to the flow chart below.) Application data MUST NOT be sent prior to the
completion of the first handshake (before a cipher suite other than completion of the first handshake (before a cipher suite other than
TLS_NULL_WITH_NULL_NULL is established). TLS_NULL_WITH_NULL_NULL is established).
Client Server Client Server
ClientHello --------> ClientHello -------->
ServerHello ServerHello
Certificate* Certificate*
ServerKeyExchange* ServerKeyExchange*
CertificateRequest* CertificateRequest*
<-------- ServerHelloDone <-------- ServerHelloDone
Certificate* Certificate*
ClientKeyExchange ClientKeyExchange
CertificateVerify* CertificateVerify*
[ChangeCipherSpec] [ChangeCipherSpec]
Finished --------> Finished -------->
[ChangeCipherSpec] [ChangeCipherSpec]
<-------- Finished <-------- Finished
Application Data <-------> Application Data Application Data <-------> Application Data
Fig. 1. Message flow for a full handshake Figure 1. Message flow for a full handshake
* Indicates optional or situation-dependent messages that are not * Indicates optional or situation-dependent messages that are not
always sent. always sent.
Note: To help avoid pipeline stalls, ChangeCipherSpec is an Note: To help avoid pipeline stalls, ChangeCipherSpec is an
independent TLS Protocol content type, and is not actually a TLS independent TLS protocol content type, and is not actually a TLS
handshake message. handshake message.
When the client and server decide to resume a previous session or When the client and server decide to resume a previous session or
duplicate an existing session (instead of negotiating new security duplicate an existing session (instead of negotiating new security
parameters), the message flow is as follows: parameters), the message flow is as follows:
The client sends a ClientHello using the Session ID of the session to The client sends a ClientHello using the Session ID of the session to
be resumed. The server then checks its session cache for a match. If be resumed. The server then checks its session cache for a match.
a match is found, and the server is willing to re-establish the If a match is found, and the server is willing to re-establish the
connection under the specified session state, it will send a connection under the specified session state, it will send a
ServerHello with the same Session ID value. At this point, both ServerHello with the same Session ID value. At this point, both
client and server MUST send ChangeCipherSpec messages and proceed client and server MUST send ChangeCipherSpec messages and proceed
directly to Finished messages. Once the re-establishment is complete, directly to Finished messages. Once the re-establishment is
the client and server MAY begin to exchange application layer data. complete, the client and server MAY begin to exchange application
(See flow chart below.) If a Session ID match is not found, the layer data. (See flow chart below.) If a Session ID match is not
server generates a new session ID and the TLS client and server found, the server generates a new session ID, and the TLS client and
perform a full handshake. server perform a full handshake.
Client Server Client Server
ClientHello --------> ClientHello -------->
ServerHello ServerHello
[ChangeCipherSpec] [ChangeCipherSpec]
<-------- Finished <-------- Finished
[ChangeCipherSpec] [ChangeCipherSpec]
Finished --------> Finished -------->
Application Data <-------> Application Data Application Data <-------> Application Data
Fig. 2. Message flow for an abbreviated handshake Figure 2. Message flow for an abbreviated handshake
The contents and significance of each message will be presented in The contents and significance of each message will be presented in
detail in the following sections. detail in the following sections.
7.4. Handshake Protocol 7.4. Handshake Protocol
The TLS Handshake Protocol is one of the defined higher-level clients The TLS Handshake Protocol is one of the defined higher-level clients
of the TLS Record Protocol. This protocol is used to negotiate the of the TLS Record Protocol. This protocol is used to negotiate the
secure attributes of a session. Handshake messages are supplied to secure attributes of a session. Handshake messages are supplied to
the TLS Record Layer, where they are encapsulated within one or more the TLS record layer, where they are encapsulated within one or more
TLSPlaintext structures, which are processed and transmitted as TLSPlaintext structures, which are processed and transmitted as
specified by the current active session state. specified by the current active session state.
enum { enum {
hello_request(0), client_hello(1), server_hello(2), hello_request(0), client_hello(1), server_hello(2),
certificate(11), server_key_exchange (12), certificate(11), server_key_exchange (12),
certificate_request(13), server_hello_done(14), certificate_request(13), server_hello_done(14),
certificate_verify(15), client_key_exchange(16), certificate_verify(15), client_key_exchange(16),
finished(20), (255) finished(20), (255)
} HandshakeType; } HandshakeType;
skipping to change at page 38, line 7 skipping to change at page 38, line 7
case certificate_request: CertificateRequest; case certificate_request: CertificateRequest;
case server_hello_done: ServerHelloDone; case server_hello_done: ServerHelloDone;
case certificate_verify: CertificateVerify; case certificate_verify: CertificateVerify;
case client_key_exchange: ClientKeyExchange; case client_key_exchange: ClientKeyExchange;
case finished: Finished; case finished: Finished;
} body; } body;
} Handshake; } Handshake;
The handshake protocol messages are presented below in the order they The handshake protocol messages are presented below in the order they
MUST be sent; sending handshake messages in an unexpected order MUST be sent; sending handshake messages in an unexpected order
results in a fatal error. Unneeded handshake messages can be omitted, results in a fatal error. Unneeded handshake messages can be
however. Note one exception to the ordering: the Certificate message omitted, however. Note one exception to the ordering: the
is used twice in the handshake (from server to client, then from Certificate message is used twice in the handshake (from server to
client to server), but described only in its first position. The one client, then from client to server), but described only in its first
message that is not bound by these ordering rules is the HelloRequest position. The one message that is not bound by these ordering rules
message, which can be sent at any time, but which SHOULD be ignored is the HelloRequest message, which can be sent at any time, but which
by the client if it arrives in the middle of a handshake. SHOULD be ignored by the client if it arrives in the middle of a
handshake.
New Handshake message types are assigned by IANA as described in New handshake message types are assigned by IANA as described in
Section 12. Section 12.
7.4.1. Hello Messages 7.4.1. Hello Messages
The hello phase messages are used to exchange security enhancement The hello phase messages are used to exchange security enhancement
capabilities between the client and server. When a new session capabilities between the client and server. When a new session
begins, the Record Layer's connection state encryption, hash, and begins, the record layer's connection state encryption, hash, and
compression algorithms are initialized to null. The current compression algorithms are initialized to null. The current
connection state is used for renegotiation messages. connection state is used for renegotiation messages.
7.4.1.1. Hello Request 7.4.1.1. Hello Request
When this message will be sent: When this message will be sent:
The HelloRequest message MAY be sent by the server at any time. The HelloRequest message MAY be sent by the server at any time.
Meaning of this message: Meaning of this message:
HelloRequest is a simple notification that the client should begin HelloRequest is a simple notification that the client should begin
the negotiation process anew. In response, the client should a the negotiation process anew. In response, the client should send
ClientHello message when convenient. This message is not intended a ClientHello message when convenient. This message is not
to establish which side is the client or server but merely to intended to establish which side is the client or server but
initiate a new negotiation. Servers SHOULD NOT send a HelloRequest merely to initiate a new negotiation. Servers SHOULD NOT send a
immediately upon the client's initial connection. It is the HelloRequest immediately upon the client's initial connection. It
client's job to send a ClientHello at that time. is the client's job to send a ClientHello at that time.
This message will be ignored by the client if the client is This message will be ignored by the client if the client is
currently negotiating a session. This message MAY be ignored by currently negotiating a session. This message MAY be ignored by
the client if it does not wish to renegotiate a session, or the the client if it does not wish to renegotiate a session, or the
client may, if it wishes, respond with a no_renegotiation alert. client may, if it wishes, respond with a no_renegotiation alert.
Since handshake messages are intended to have transmission Since handshake messages are intended to have transmission
precedence over application data, it is expected that the precedence over application data, it is expected that the
negotiation will begin before no more than a few records are negotiation will begin before no more than a few records are
received from the client. If the server sends a HelloRequest but received from the client. If the server sends a HelloRequest but
does not receive a ClientHello in response, it may close the does not receive a ClientHello in response, it may close the
connection with a fatal alert. connection with a fatal alert.
After sending a HelloRequest, servers SHOULD NOT repeat the After sending a HelloRequest, servers SHOULD NOT repeat the
request until the subsequent handshake negotiation is complete. request until the subsequent handshake negotiation is complete.
Structure of this message: Structure of this message:
struct { } HelloRequest; struct { } HelloRequest;
This message MUST NOT be included in the message hashes that are This message MUST NOT be included in the message hashes that are
maintained throughout the handshake and used in the finished messages maintained throughout the handshake and used in the Finished messages
and the certificate verify message. and the certificate verify message.
7.4.1.2. Client Hello 7.4.1.2. Client Hello
When this message will be sent: When this message will be sent:
When a client first connects to a server it is required to send When a client first connects to a server, it is required to send
the ClientHello as its first message. The client can also send a the ClientHello as its first message. The client can also send a
ClientHello in response to a HelloRequest or on its own initiative ClientHello in response to a HelloRequest or on its own initiative
in order to renegotiate the security parameters in an existing in order to renegotiate the security parameters in an existing
connection. connection.
Structure of this message: Structure of this message:
The ClientHello message includes a random structure, which is used The ClientHello message includes a random structure, which is used
later in the protocol. later in the protocol.
struct { struct {
uint32 gmt_unix_time; uint32 gmt_unix_time;
opaque random_bytes[28]; opaque random_bytes[28];
} Random; } Random;
gmt_unix_time gmt_unix_time
The current time and date in standard UNIX 32-bit format The current time and date in standard UNIX 32-bit format
(seconds since the midnight starting Jan 1, 1970, UTC, ignoring (seconds since the midnight starting Jan 1, 1970, UTC, ignoring
leap seconds) according to the sender's internal clock. Clocks leap seconds) according to the sender's internal clock. Clocks
are not required to be set correctly by the basic TLS Protocol; are not required to be set correctly by the basic TLS protocol;
higher-level or application protocols may define additional higher-level or application protocols may define additional
requirements. Note that, for historical reasons, the data requirements. Note that, for historical reasons, the data
element is named using GMT, the predecessor of the current element is named using GMT, the predecessor of the current
worldwide time base, UTC. worldwide time base, UTC.
random_bytes random_bytes
28 bytes generated by a secure random number generator. 28 bytes generated by a secure random number generator.
The ClientHello message includes a variable-length session The ClientHello message includes a variable-length session
identifier. If not empty, the value identifies a session between the identifier. If not empty, the value identifies a session between the
same client and server whose security parameters the client wishes to same client and server whose security parameters the client wishes to
reuse. The session identifier MAY be from an earlier connection, this reuse. The session identifier MAY be from an earlier connection,
connection, or from another currently active connection. The second this connection, or from another currently active connection. The
option is useful if the client only wishes to update the random second option is useful if the client only wishes to update the
structures and derived values of a connection, and the third option random structures and derived values of a connection, and the third
makes it possible to establish several independent secure connections option makes it possible to establish several independent secure
without repeating the full handshake protocol. These independent connections without repeating the full handshake protocol. These
connections may occur sequentially or simultaneously; a SessionID independent connections may occur sequentially or simultaneously; a
becomes valid when the handshake negotiating it completes with the SessionID becomes valid when the handshake negotiating it completes
exchange of Finished messages and persists until it is removed due to with the exchange of Finished messages and persists until it is
aging or because a fatal error was encountered on a connection removed due to aging or because a fatal error was encountered on a
associated with the session. The actual contents of the SessionID are connection associated with the session. The actual contents of the
defined by the server. SessionID are defined by the server.
opaque SessionID<0..32>; opaque SessionID<0..32>;
Warning: Because the SessionID is transmitted without encryption or Warning: Because the SessionID is transmitted without encryption or
immediate MAC protection, servers MUST NOT place confidential immediate MAC protection, servers MUST NOT place confidential
information in session identifiers or let the contents of fake information in session identifiers or let the contents of fake
session identifiers cause any breach of security. (Note that the session identifiers cause any breach of security. (Note that the
content of the handshake as a whole, including the SessionID, is content of the handshake as a whole, including the SessionID, is
protected by the Finished messages exchanged at the end of the protected by the Finished messages exchanged at the end of the
handshake.) handshake.)
The cipher suite list, passed from the client to the server in the The cipher suite list, passed from the client to the server in the
ClientHello message, contains the combinations of cryptographic ClientHello message, contains the combinations of cryptographic
algorithms supported by the client in order of the client's algorithms supported by the client in order of the client's
preference (favorite choice first). Each cipher suite defines a key preference (favorite choice first). Each cipher suite defines a key
exchange algorithm, a bulk encryption algorithm (including secret key exchange algorithm, a bulk encryption algorithm (including secret key
length), a MAC algorithm, and a PRF. The server will select a cipher length), a MAC algorithm, and a PRF. The server will select a cipher
suite or, if no acceptable choices are presented, return a handshake suite or, if no acceptable choices are presented, return a handshake
failure alert and close the connection. If the list contains cipher failure alert and close the connection. If the list contains cipher
suites the server does not recognize, support, or wish to use, the suites the server does not recognize, support, or wish to use, the
server MUST ignore those cipher suites, and process the remaining server MUST ignore those cipher suites, and process the remaining
ones as usual. ones as usual.
uint8 CipherSuite[2]; /* Cryptographic suite selector */ uint8 CipherSuite[2]; /* Cryptographic suite selector */
skipping to change at page 41, line 12 skipping to change at page 41, line 19
CompressionMethod compression_methods<1..2^8-1>; CompressionMethod compression_methods<1..2^8-1>;
select (extensions_present) { select (extensions_present) {
case false: case false:
struct {}; struct {};
case true: case true:
Extension extensions<0..2^16-1>; Extension extensions<0..2^16-1>;
}; };
} ClientHello; } ClientHello;
TLS allows extensions to follow the compression_methods field in an TLS allows extensions to follow the compression_methods field in an
extensions block. The presence of extensions can be detected by extensions block. The presence of extensions can be detected by
determining whether there are bytes following the compression_methods determining whether there are bytes following the compression_methods
at the end of the ClientHello. Note that this method of detecting at the end of the ClientHello. Note that this method of detecting
optional data differs from the normal TLS method of having a optional data differs from the normal TLS method of having a
variable-length field but is used for compatibility with TLS before variable-length field, but it is used for compatibility with TLS
extensions were defined. before extensions were defined.
client_version client_version
The version of the TLS protocol by which the client wishes to The version of the TLS protocol by which the client wishes to
communicate during this session. This SHOULD be the latest communicate during this session. This SHOULD be the latest
(highest valued) version supported by the client. For this version (highest valued) version supported by the client. For this
of the specification, the version will be 3.3 (See Appendix E for version of the specification, the version will be 3.3 (see
details about backward compatibility). Appendix E for details about backward compatibility).
random random
A client-generated random structure. A client-generated random structure.
session_id session_id
The ID of a session the client wishes to use for this connection. The ID of a session the client wishes to use for this connection.
This field is empty if no session_id is available, or if the This field is empty if no session_id is available, or if the
client wishes to generate new security parameters. client wishes to generate new security parameters.
cipher_suites cipher_suites
This is a list of the cryptographic options supported by the This is a list of the cryptographic options supported by the
client, with the client's first preference first. If the client, with the client's first preference first. If the
session_id field is not empty (implying a session resumption session_id field is not empty (implying a session resumption
request), this vector MUST include at least the cipher_suite from request), this vector MUST include at least the cipher_suite from
that session. Values are defined in Appendix A.5. that session. Values are defined in Appendix A.5.
compression_methods compression_methods
This is a list of the compression methods supported by the client, This is a list of the compression methods supported by the client,
sorted by client preference. If the session_id field is not empty sorted by client preference. If the session_id field is not empty
(implying a session resumption request), it MUST include the (implying a session resumption request), it MUST include the
compression_method from that session. This vector MUST contain, compression_method from that session. This vector MUST contain,
and all implementations MUST support, CompressionMethod.null. and all implementations MUST support, CompressionMethod.null.
Thus, a client and server will always be able to agree on a Thus, a client and server will always be able to agree on a
compression method. compression method.
extensions extensions
Clients MAY request extended functionality from servers by sending Clients MAY request extended functionality from servers by sending
data in the extensions field. The actual "Extension" format is data in the extensions field. The actual "Extension" format is
defined in Section 7.4.1.4. defined in Section 7.4.1.4.
In the event that a client requests additional functionality using In the event that a client requests additional functionality using
extensions, and this functionality is not supplied by the server, the extensions, and this functionality is not supplied by the server, the
client MAY abort the handshake. A server MUST accept client hello client MAY abort the handshake. A server MUST accept ClientHello
messages both with and without the extensions field, and (as for all messages both with and without the extensions field, and (as for all
other messages) MUST check that the amount of data in the message other messages) it MUST check that the amount of data in the message
precisely matches one of these formats; if not, then it MUST send a precisely matches one of these formats; if not, then it MUST send a
fatal "decode_error" alert. fatal "decode_error" alert.
After sending the client hello message, the client waits for a After sending the ClientHello message, the client waits for a
ServerHello message. Any other handshake message returned by the ServerHello message. Any handshake message returned by the server,
server except for a HelloRequest is treated as a fatal error. except for a HelloRequest, is treated as a fatal error.
7.4.1.3. Server Hello 7.4.1.3. Server Hello
When this message will be sent: When this message will be sent:
The server will send this message in response to a ClientHello The server will send this message in response to a ClientHello
message when it was able to find an acceptable set of algorithms. message when it was able to find an acceptable set of algorithms.
If it cannot find such a match, it will respond with a handshake If it cannot find such a match, it will respond with a handshake
failure alert. failure alert.
Structure of this message: Structure of this message:
skipping to change at page 42, line 50 skipping to change at page 43, line 11
Extension extensions<0..2^16-1>; Extension extensions<0..2^16-1>;
}; };
} ServerHello; } ServerHello;
The presence of extensions can be detected by determining whether The presence of extensions can be detected by determining whether
there are bytes following the compression_method field at the end of there are bytes following the compression_method field at the end of
the ServerHello. the ServerHello.
server_version server_version
This field will contain the lower of that suggested by the client This field will contain the lower of that suggested by the client
in the client hello and the highest supported by the server. For in the client hello and the highest supported by the server. For
this version of the specification, the version is 3.3. (See this version of the specification, the version is 3.3. (See
Appendix E for details about backward compatibility.) Appendix E for details about backward compatibility.)
random random
This structure is generated by the server and MUST be This structure is generated by the server and MUST be
independently generated from the ClientHello.random. independently generated from the ClientHello.random.
session_id session_id
This is the identity of the session corresponding to this This is the identity of the session corresponding to this
connection. If the ClientHello.session_id was non-empty, the connection. If the ClientHello.session_id was non-empty, the
server will look in its session cache for a match. If a match is server will look in its session cache for a match. If a match is
found and the server is willing to establish the new connection found and the server is willing to establish the new connection
using the specified session state, the server will respond with using the specified session state, the server will respond with
the same value as was supplied by the client. This indicates a the same value as was supplied by the client. This indicates a
resumed session and dictates that the parties must proceed resumed session and dictates that the parties must proceed
directly to the finished messages. Otherwise this field will directly to the Finished messages. Otherwise, this field will
contain a different value identifying the new session. The server contain a different value identifying the new session. The server
may return an empty session_id to indicate that the session will may return an empty session_id to indicate that the session will
not be cached and therefore cannot be resumed. If a session is not be cached and therefore cannot be resumed. If a session is
resumed, it must be resumed using the same cipher suite it was resumed, it must be resumed using the same cipher suite it was
originally negotiated with. Note that there is no requirement that originally negotiated with. Note that there is no requirement
the server resume any session even if it had formerly provided a that the server resume any session even if it had formerly
session_id. Clients MUST be prepared to do a full negotiation -- provided a session_id. Clients MUST be prepared to do a full
including negotiating new cipher suites -- during any handshake. negotiation -- including negotiating new cipher suites -- during
any handshake.
cipher_suite cipher_suite
The single cipher suite selected by the server from the list in The single cipher suite selected by the server from the list in
ClientHello.cipher_suites. For resumed sessions, this field is the ClientHello.cipher_suites. For resumed sessions, this field is
value from the state of the session being resumed. the value from the state of the session being resumed.
compression_method compression_method
The single compression algorithm selected by the server from the The single compression algorithm selected by the server from the
list in ClientHello.compression_methods. For resumed sessions this list in ClientHello.compression_methods. For resumed sessions,
field is the value from the resumed session state. this field is the value from the resumed session state.
extensions extensions
A list of extensions. Note that only extensions offered by the A list of extensions. Note that only extensions offered by the
client can appear in the server's list. client can appear in the server's list.
7.4.1.4 Hello Extensions 7.4.1.4. Hello Extensions
The extension format is: The extension format is:
struct { struct {
ExtensionType extension_type; ExtensionType extension_type;
opaque extension_data<0..2^16-1>; opaque extension_data<0..2^16-1>;
} Extension; } Extension;
enum { enum {
signature_algorithms(TBD-BY-IANA), (65535) signature_algorithms(13), (65535)
} ExtensionType; } ExtensionType;
Here: Here:
- "extension_type" identifies the particular extension type. - "extension_type" identifies the particular extension type.
- "extension_data" contains information specific to the particular - "extension_data" contains information specific to the particular
extension type. extension type.
The initial set of extensions is defined in a companion document The initial set of extensions is defined in a companion document
[TLSEXT]. The list of extension types is maintained by IANA as [TLSEXT]. The list of extension types is maintained by IANA as
described in Section 12. described in Section 12.
An extension type MUST NOT appear in the ServerHello unless the same
extension type appeared in the corresponding ClientHello. If a
client receives an extension type in ServerHello that it did not
request in the associated ClientHello, it MUST abort the handshake
with an unsupported_extension fatal alert.
Nonetheless, "server-oriented" extensions may be provided in the
future within this framework. Such an extension (say, of type x)
would require the client to first send an extension of type x in a
ClientHello with empty extension_data to indicate that it supports
the extension type. In this case, the client is offering the
capability to understand the extension type, and the server is taking
the client up on its offer.
When multiple extensions of different types are present in the
ClientHello or ServerHello messages, the extensions MAY appear in any
order. There MUST NOT be more than one extension of the same type.
Finally, note that extensions can be sent both when starting a new
session and when requesting session resumption. Indeed, a client
that requests session resumption does not in general know whether the
server will accept this request, and therefore it SHOULD send the
same extensions as it would send if it were not attempting
resumption.
In general, the specification of each extension type needs to
describe the effect of the extension both during full handshake and
session resumption. Most current TLS extensions are relevant only
when a session is initiated: when an older session is resumed, the
server does not process these extensions in Client Hello, and does
not include them in Server Hello. However, some extensions may
specify different behavior during session resumption.
There are subtle (and not so subtle) interactions that may occur in There are subtle (and not so subtle) interactions that may occur in
this protocol between new features and existing features which may this protocol between new features and existing features which may
result in a significant reduction in overall security. The following result in a significant reduction in overall security. The following
considerations should be taken into account when designing new considerations should be taken into account when designing new
extensions: extensions:
- Some cases where a server does not agree to an extension are error - Some cases where a server does not agree to an extension are error
conditions, and some simply a refusal to support a particular conditions, and some are simply refusals to support particular
feature. In general error alerts should be used for the former, features. In general, error alerts should be used for the former,
and a field in the server extension response for the latter. and a field in the server extension response for the latter.
- Extensions should as far as possible be designed to prevent any - Extensions should, as far as possible, be designed to prevent any
attack that forces use (or non-use) of a particular feature by attack that forces use (or non-use) of a particular feature by
manipulation of handshake messages. This principle should be manipulation of handshake messages. This principle should be
followed regardless of whether the feature is believed to cause a followed regardless of whether the feature is believed to cause a
security problem. security problem.
Often the fact that the extension fields are included in the Often the fact that the extension fields are included in the
inputs to the Finished message hashes will be sufficient, but inputs to the Finished message hashes will be sufficient, but
extreme care is needed when the extension changes the meaning of extreme care is needed when the extension changes the meaning of
messages sent in the handshake phase. Designers and implementors messages sent in the handshake phase. Designers and implementors
should be aware of the fact that until the handshake has been should be aware of the fact that until the handshake has been
authenticated, active attackers can modify messages and insert, authenticated, active attackers can modify messages and insert,
remove, or replace extensions. remove, or replace extensions.
- It would be technically possible to use extensions to change major - It would be technically possible to use extensions to change major
aspects of the design of TLS; for example the design of cipher aspects of the design of TLS; for example the design of cipher
suite negotiation. This is not recommended; it would be more suite negotiation. This is not recommended; it would be more
appropriate to define a new version of TLS - particularly since appropriate to define a new version of TLS -- particularly since
the TLS handshake algorithms have specific protection against the TLS handshake algorithms have specific protection against
version rollback attacks based on the version number, and the version rollback attacks based on the version number, and the
possibility of version rollback should be a significant possibility of version rollback should be a significant
consideration in any major design change. consideration in any major design change.
7.4.1.4.1 Signature Algorithms 7.4.1.4.1. Signature Algorithms
The client uses the "signature_algorithms" extension to indicate to The client uses the "signature_algorithms" extension to indicate to
the server which signature/hash algorithm pairs may be used in the server which signature/hash algorithm pairs may be used in
digital signatures. The "extension_data" field of this extension digital signatures. The "extension_data" field of this extension
contains a "supported_signature_algorithms" value. contains a "supported_signature_algorithms" value.
enum { enum {
none(0), md5(1), sha1(2), sha224(3), sha256(4), sha384(5), none(0), md5(1), sha1(2), sha224(3), sha256(4), sha384(5),
sha512(6), (255) sha512(6), (255)
} HashAlgorithm; } HashAlgorithm;
enum { anonymous(0), rsa(1), dsa(2), ecdsa(3), (255) } enum { anonymous(0), rsa(1), dsa(2), ecdsa(3), (255) }
SignatureAlgorithm; SignatureAlgorithm;
struct { struct {
HashAlgorithm hash; HashAlgorithm hash;
SignatureAlgorithm signature; SignatureAlgorithm signature;
} SignatureAndHashAlgorithm; } SignatureAndHashAlgorithm;
SignatureAndHashAlgorithm SignatureAndHashAlgorithm
supported_signature_algorithms<2..2^16-2>; supported_signature_algorithms<2..2^16-2>;
Each SignatureAndHashAlgorithm value lists a single hash/signature Each SignatureAndHashAlgorithm value lists a single hash/signature
pair which the client is willing to verify. The values are indicated pair that the client is willing to verify. The values are indicated
in descending order of preference. in descending order of preference.
Note: Because not all signature algorithms and hash algorithms may be Note: Because not all signature algorithms and hash algorithms may be
accepted by an implementation (e.g., DSA with SHA-1, but not accepted by an implementation (e.g., DSA with SHA-1, but not
SHA-256), algorithms here are listed in pairs. SHA-256), algorithms here are listed in pairs.
hash hash
This field indicates the hash algorithm which may be used. The This field indicates the hash algorithm which may be used. The
values indicate support for unhashed data, MD5 [MD5], SHA-1, values indicate support for unhashed data, MD5 [MD5], SHA-1,
SHA-224, SHA-256, SHA-384, and SHA-512 [SHS] respectively. The SHA-224, SHA-256, SHA-384, and SHA-512 [SHS], respectively. The
"none" value is provided for future extensibility, in case of a "none" value is provided for future extensibility, in case of a
signature algorithm which does not require hashing before signing. signature algorithm which does not require hashing before signing.
signature signature
This field indicates the signature algorithm which may be used. This field indicates the signature algorithm that may be used.
The values indicate anonymous signatures, RSASSA-PKCS1-v1_5 The values indicate anonymous signatures, RSASSA-PKCS1-v1_5
[PKCS1] and DSA [DSS], and ECDSA [ECDSA], respectively. The [PKCS1] and DSA [DSS], and ECDSA [ECDSA], respectively. The
"anonymous" value is meaningless in this context but used in "anonymous" value is meaningless in this context but used in
Section 7.4.3. It MUST NOT appear in this extension. Section 7.4.3. It MUST NOT appear in this extension.
The semantics of this extension are somewhat complicated because the The semantics of this extension are somewhat complicated because the
cipher suite indicates permissible signature algorithms but not hash cipher suite indicates permissible signature algorithms but not hash
algorithms. Sections 7.4.2 and 7.4.3 describe the appropriate rules. algorithms. Sections 7.4.2 and 7.4.3 describe the appropriate rules.
If the client supports only the default hash and signature algorithms If the client supports only the default hash and signature algorithms
(listed in this section), it MAY omit the signature_algorithms (listed in this section), it MAY omit the signature_algorithms
extension. If the client does not support the default algorithms, or extension. If the client does not support the default algorithms, or
supports other hash and signature algorithms (and it is willing to supports other hash and signature algorithms (and it is willing to
use them for verifying messages sent by the server, i.e., server use them for verifying messages sent by the server, i.e., server
certificates and server key exchange), it MUST send the certificates and server key exchange), it MUST send the
signature_algorithms extension, listing the algorithms it is willing signature_algorithms extension, listing the algorithms it is willing
to accept. to accept.
If the client does not send the signature_algorithms extension, the If the client does not send the signature_algorithms extension, the
server MUST assume the following: server MUST do the following:
- If the negotiated key exchange algorithm is one of (RSA, DHE_RSA, - If the negotiated key exchange algorithm is one of (RSA, DHE_RSA,
DH_RSA, RSA_PSK, ECDH_RSA, ECDHE_RSA), behave as if client had sent DH_RSA, RSA_PSK, ECDH_RSA, ECDHE_RSA), behave as if client had
the value {sha1,rsa}. sent the value {sha1,rsa}.
- If the negotiated key exchange algorithm is one of (DHE_DSS, - If the negotiated key exchange algorithm is one of (DHE_DSS,
DH_DSS), behave as if the client had sent the value {sha1,dsa}. DH_DSS), behave as if the client had sent the value {sha1,dsa}.
- If the negotiated key exchange algorithm is one of (ECDH_ECDSA, - If the negotiated key exchange algorithm is one of (ECDH_ECDSA,
ECDHE_ECDSA), behave as if the client had sent value {sha1,ecdsa}. ECDHE_ECDSA), behave as if the client had sent value {sha1,ecdsa}.
Note: this is a change from TLS 1.1 where there are no explicit rules Note: this is a change from TLS 1.1 where there are no explicit
but as a practical matter one can assume that the peer supports MD5 rules, but as a practical matter one can assume that the peer
and SHA-1. supports MD5 and SHA-1.
Note: this extension is not meaningful for TLS versions prior to 1.2. Note: this extension is not meaningful for TLS versions prior to 1.2.
Clients MUST NOT offer it if they are offering prior versions. Clients MUST NOT offer it if they are offering prior versions.
However, even if clients do offer it, the rules specified in [TLSEXT] However, even if clients do offer it, the rules specified in [TLSEXT]
require servers to ignore extensions they do not understand. require servers to ignore extensions they do not understand.
Servers MUST NOT send this extension. TLS servers MUST support Servers MUST NOT send this extension. TLS servers MUST support
receiving this extension. receiving this extension.
7.4.2. Server Certificate When performing session resumption, this extension is not included in
Server Hello, and the server ignores the extension in Client Hello
(if present).
7.4.2. Server Certificate
When this message will be sent: When this message will be sent:
The server MUST send a Certificate message whenever the agreed- The server MUST send a Certificate message whenever the agreed-
upon key exchange method uses certificates for authentication upon key exchange method uses certificates for authentication
(this includes all key exchange methods defined in this document (this includes all key exchange methods defined in this document
except DH_anon). This message will always immediately follow the except DH_anon). This message will always immediately follow the
server hello message. ServerHello message.
Meaning of this message: Meaning of this message:
This message conveys the server's certificate chain to the client. This message conveys the server's certificate chain to the client.
The certificate MUST be appropriate for the negotiated cipher The certificate MUST be appropriate for the negotiated cipher
suite's key exchange algorithm, and any negotiated extensions. suite's key exchange algorithm and any negotiated extensions.
Structure of this message: Structure of this message:
opaque ASN.1Cert<1..2^24-1>; opaque ASN.1Cert<1..2^24-1>;
struct { struct {
ASN.1Cert certificate_list<0..2^24-1>; ASN.1Cert certificate_list<0..2^24-1>;
} Certificate; } Certificate;
certificate_list certificate_list
This is a sequence (chain) of certificates. The sender's This is a sequence (chain) of certificates. The sender's
certificate MUST come first in the list. Each following certificate MUST come first in the list. Each following
certificate MUST directly certify the one preceding it. Because certificate MUST directly certify the one preceding it. Because
certificate validation requires that root keys be distributed certificate validation requires that root keys be distributed
independently, the self-signed certificate that specifies the root independently, the self-signed certificate that specifies the root
certificate authority MAY be omitted from the chain, under the certificate authority MAY be omitted from the chain, under the
assumption that the remote end must already possess it in order to assumption that the remote end must already possess it in order to
validate it in any case. validate it in any case.
The same message type and structure will be used for the client's The same message type and structure will be used for the client's
response to a certificate request message. Note that a client MAY response to a certificate request message. Note that a client MAY
send no certificates if it does not have an appropriate certificate send no certificates if it does not have an appropriate certificate
to send in response to the server's authentication request. to send in response to the server's authentication request.
Note: PKCS #7 [PKCS7] is not used as the format for the certificate Note: PKCS #7 [PKCS7] is not used as the format for the certificate
vector because PKCS #6 [PKCS6] extended certificates are not used. vector because PKCS #6 [PKCS6] extended certificates are not used.
Also, PKCS #7 defines a SET rather than a SEQUENCE, making the task Also, PKCS #7 defines a SET rather than a SEQUENCE, making the task
of parsing the list more difficult. of parsing the list more difficult.
The following rules apply to the certificates sent by the server: The following rules apply to the certificates sent by the server:
- The certificate type MUST be X.509v3, unless explicitly negotiated - The certificate type MUST be X.509v3, unless explicitly negotiated
otherwise (e.g., [TLSPGP]). otherwise (e.g., [TLSPGP]).
- The end entity certificate's public key (and associated - The end entity certificate's public key (and associated
restrictions) MUST be compatible with the selected key exchange restrictions) MUST be compatible with the selected key exchange
algorithm. algorithm.
Key Exchange Alg. Certificate Key Type Key Exchange Alg. Certificate Key Type
RSA RSA public key; the certificate MUST RSA RSA public key; the certificate MUST allow the
RSA_PSK allow the key to be used for encryption RSA_PSK key to be used for encryption (the
(the keyEncipherment bit MUST be set keyEncipherment bit MUST be set if the key
if the key usage extension is present). usage extension is present).
Note: RSA_PSK is defined in [TLSPSK]. Note: RSA_PSK is defined in [TLSPSK].
DHE_RSA RSA public key; the certificate MUST DHE_RSA RSA public key; the certificate MUST allow the
ECDHE_RSA allow the key to be used for signing ECDHE_RSA key to be used for signing (the
(the digitalSignature bit MUST be set digitalSignature bit MUST be set if the key
if the key usage extension is present) usage extension is present) with the signature
with the signature scheme and hash scheme and hash algorithm that will be employed
algorithm that will be employed in the
server key exchange message.
Note: ECDHE_RSA is defined in [TLSECC].
DHE_DSS DSA public key; the certificate MUST
allow the key to be used for signing with
the hash algorithm that will be employed
in the server key exchange message. in the server key exchange message.
Note: ECDHE_RSA is defined in [TLSECC].
DH_DSS Diffie-Hellman public key; the DHE_DSS DSA public key; the certificate MUST allow the
DH_RSA keyAgreement bit MUST be set if the key to be used for signing with the hash
key usage extension is present. algorithm that will be employed in the server
key exchange message.
ECDH_ECDSA ECDH-capable public key; the public key DH_DSS Diffie-Hellman public key; the keyAgreement bit
ECDH_RSA MUST use a curve and point format supported DH_RSA MUST be set if the key usage extension is
by the client, as described in [TLSECC]. present.
ECDHE_ECDSA ECDSA-capable public key; the certificate ECDH_ECDSA ECDH-capable public key; the public key MUST
MUST allow the key to be used for signing ECDH_RSA use a curve and point format supported by the
with the hash algorithm that will be client, as described in [TLSECC].
employed in the server key exchange
message. The public key MUST use a curve ECDHE_ECDSA ECDSA-capable public key; the certificate MUST
and point format supported by the client, allow the key to be used for signing with the
as described in [TLSECC]. hash algorithm that will be employed in the
server key exchange message. The public key
MUST use a curve and point format supported by
the client, as described in [TLSECC].
- The "server_name" and "trusted_ca_keys" extensions [TLSEXT] are - The "server_name" and "trusted_ca_keys" extensions [TLSEXT] are
used to guide certificate selection. used to guide certificate selection.
If the client provided a "signature_algorithms" extension, then all If the client provided a "signature_algorithms" extension, then all
certificates provided by the server MUST be signed by a certificates provided by the server MUST be signed by a
hash/signature algorithm pair that appears in that extension. Note hash/signature algorithm pair that appears in that extension. Note
that this implies that a certificate containing a key for one that this implies that a certificate containing a key for one
signature algorithm MAY be signed using a different signature signature algorithm MAY be signed using a different signature
algorithm (for instance, an RSA key signed with a DSA key.) This is a algorithm (for instance, an RSA key signed with a DSA key). This is
departure from TLS 1.1, which required that the algorithms be the a departure from TLS 1.1, which required that the algorithms be the
same. Note that this also implies that the DH_DSS, DH_RSA, same. Note that this also implies that the DH_DSS, DH_RSA,
ECDH_ECDSA, and ECDH_RSA key exchange algorithms do not restrict the ECDH_ECDSA, and ECDH_RSA key exchange algorithms do not restrict the
algorithm used to sign the certificate. Fixed DH certificates MAY be algorithm used to sign the certificate. Fixed DH certificates MAY be
signed with any hash/signature algorithm pair appearing in the signed with any hash/signature algorithm pair appearing in the
extension. The names DH_DSS, DH_RSA, ECDH_ECDSA, and ECDH_RSA are extension. The names DH_DSS, DH_RSA, ECDH_ECDSA, and ECDH_RSA are
historical. historical.
If the server has multiple certificates, it chooses one of them based If the server has multiple certificates, it chooses one of them based
on the above-mentioned criteria (in addition to other criteria, such on the above-mentioned criteria (in addition to other criteria, such
as transport layer endpoint, local configuration and preferences, as transport layer endpoint, local configuration and preferences,
etc.). If the server has a single certificate it SHOULD attempt to etc.). If the server has a single certificate, it SHOULD attempt to
validate that it meets these criteria. validate that it meets these criteria.
Note that there are certificates that use algorithms and/or algorithm Note that there are certificates that use algorithms and/or algorithm
combinations that cannot be currently used with TLS. For example, a combinations that cannot be currently used with TLS. For example, a
certificate with RSASSA-PSS signature key (id-RSASSA-PSS OID in certificate with RSASSA-PSS signature key (id-RSASSA-PSS OID in
SubjectPublicKeyInfo) cannot be used because TLS defines no SubjectPublicKeyInfo) cannot be used because TLS defines no
corresponding signature algorithm. corresponding signature algorithm.
As cipher suites that specify new key exchange methods are specified As cipher suites that specify new key exchange methods are specified
for the TLS Protocol, they will the imply certificate format and the for the TLS protocol, they will imply the certificate format and the
required encoded keying information. required encoded keying information.
7.4.3. Server Key Exchange Message 7.4.3. Server Key Exchange Message
When this message will be sent: When this message will be sent:
This message will be sent immediately after the server Certificate This message will be sent immediately after the server Certificate
message (or the ServerHello message, if this is an anonymous message (or the ServerHello message, if this is an anonymous
negotiation). negotiation).
The ServerKeyExchange message is sent by the server only when the The ServerKeyExchange message is sent by the server only when the
server Certificate message (if sent) does not contain enough data server Certificate message (if sent) does not contain enough data
to allow the client to exchange a premaster secret. This is true to allow the client to exchange a premaster secret. This is true
for the following key exchange methods: for the following key exchange methods:
DHE_DSS DHE_DSS
DHE_RSA DHE_RSA
DH_anon DH_anon
It is not legal to send the ServerKeyExchange message for the It is not legal to send the ServerKeyExchange message for the
following key exchange methods: following key exchange methods:
RSA RSA
DH_DSS DH_DSS
DH_RSA DH_RSA
Other key exchange algorithms, such as those defined in Other key exchange algorithms, such as those defined in [TLSECC],
[TLSECC], MUST specify whether the ServerKeyExchange message is MUST specify whether the ServerKeyExchange message is sent or not;
sent or not; and if the message is sent, its contents. and if the message is sent, its contents.
Meaning of this message: Meaning of this message:
This message conveys cryptographic information to allow the client This message conveys cryptographic information to allow the client
to communicate the premaster secret: a Diffie-Hellman public key to communicate the premaster secret: a Diffie-Hellman public key
with which the client can complete a key exchange (with the result with which the client can complete a key exchange (with the result
being the premaster secret) or a public key for some other being the premaster secret) or a public key for some other
algorithm. algorithm.
Structure of this message: Structure of this message:
enum { dhe_dss, dhe_rsa, dh_anon, rsa, dh_dss, dh_rsa enum { dhe_dss, dhe_rsa, dh_anon, rsa, dh_dss, dh_rsa
/* may be extended, e.g. for ECDH -- see [TLSECC] */ /* may be extended, e.g., for ECDH -- see [TLSECC] */
} KeyExchangeAlgorithm; } KeyExchangeAlgorithm;
struct { struct {
opaque dh_p<1..2^16-1>; opaque dh_p<1..2^16-1>;
opaque dh_g<1..2^16-1>; opaque dh_g<1..2^16-1>;
opaque dh_Ys<1..2^16-1>; opaque dh_Ys<1..2^16-1>;
} ServerDHParams; /* Ephemeral DH parameters */ } ServerDHParams; /* Ephemeral DH parameters */
dh_p dh_p
The prime modulus used for the Diffie-Hellman operation. The prime modulus used for the Diffie-Hellman operation.
skipping to change at page 50, line 45 skipping to change at page 52, line 22
digitally-signed struct { digitally-signed struct {
opaque client_random[32]; opaque client_random[32];
opaque server_random[32]; opaque server_random[32];
ServerDHParams params; ServerDHParams params;
} signed_params; } signed_params;
case rsa: case rsa:
case dh_dss: case dh_dss:
case dh_rsa: case dh_rsa:
struct {} ; struct {} ;
/* message is omitted for rsa, dh_dss, and dh_rsa */ /* message is omitted for rsa, dh_dss, and dh_rsa */
/* may be extended, e.g. for ECDH -- see [TLSECC] */ /* may be extended, e.g., for ECDH -- see [TLSECC] */
}; };
} ServerKeyExchange; } ServerKeyExchange;
params params
The server's key exchange parameters. The server's key exchange parameters.
signed_params signed_params
For non-anonymous key exchanges, a signature over the For non-anonymous key exchanges, a signature over the server's
server's key exchange parameters. key exchange parameters.
If the client has offered the "signature_algorithms" extension, the If the client has offered the "signature_algorithms" extension, the
signature algorithm and hash algorithm MUST be a pair listed in that signature algorithm and hash algorithm MUST be a pair listed in that
extension. Note that there is a possibility for inconsistencies here. extension. Note that there is a possibility for inconsistencies
For instance, the client might offer DHE_DSS key exchange but omit here. For instance, the client might offer DHE_DSS key exchange but
any DSA pairs from its "signature_algorithms" extension. In order to omit any DSA pairs from its "signature_algorithms" extension. In
negotiate correctly, the server MUST check any candidate cipher order to negotiate correctly, the server MUST check any candidate
suites against the "signature_algorithms" extension before selecting cipher suites against the "signature_algorithms" extension before
them. This is somewhat inelegant but is a compromise designed to selecting them. This is somewhat inelegant but is a compromise
minimize changes to the original cipher suite design. designed to minimize changes to the original cipher suite design.
In addition, the hash and signature algorithms MUST be compatible In addition, the hash and signature algorithms MUST be compatible
with the key in the server's end-entity certificate. RSA keys MAY be with the key in the server's end-entity certificate. RSA keys MAY be
used with any permitted hash algorithm, subject to restrictions in used with any permitted hash algorithm, subject to restrictions in
the certificate, if any. the certificate, if any.
Because DSA signatures do not contain any secure indication of hash Because DSA signatures do not contain any secure indication of hash
algorithm, there is a risk of hash substitution if multiple hashes algorithm, there is a risk of hash substitution if multiple hashes
may be used with any key. Currently, DSA [DSS] may only be used with may be used with any key. Currently, DSA [DSS] may only be used with
SHA-1. Future revisions of DSS [DSS-3] are expected to allow the use SHA-1. Future revisions of DSS [DSS-3] are expected to allow the use
of other digest algorithms with DSA, as well as guidance as to which of other digest algorithms with DSA, as well as guidance as to which
digest algorithms should be used with each key size. In addition, digest algorithms should be used with each key size. In addition,
future revisions of [PKIX] may specify mechanisms for certificates to future revisions of [PKIX] may specify mechanisms for certificates to
indicate which digest algorithms are to be used with DSA. indicate which digest algorithms are to be used with DSA.
As additional cipher suites are defined for TLS that include new key As additional cipher suites are defined for TLS that include new key
exchange algorithms, the server key exchange message will be sent if exchange algorithms, the server key exchange message will be sent if
and only if the certificate type associated with the key exchange and only if the certificate type associated with the key exchange
algorithm does not provide enough information for the client to algorithm does not provide enough information for the client to
exchange a premaster secret. exchange a premaster secret.
7.4.4. Certificate Request 7.4.4. Certificate Request
When this message will be sent: When this message will be sent:
A non-anonymous server can optionally request a certificate from A non-anonymous server can optionally request a certificate from
the client, if appropriate for the selected cipher suite. This the client, if appropriate for the selected cipher suite. This
message, if sent, will immediately follow the ServerKeyExchange message, if sent, will immediately follow the ServerKeyExchange
message (if it is sent; otherwise, the server's Certificate message (if it is sent; otherwise, this message follows the
message). server's Certificate message).
Structure of this message: Structure of this message:
enum { enum {
rsa_sign(1), dss_sign(2), rsa_fixed_dh(3), dss_fixed_dh(4), rsa_sign(1), dss_sign(2), rsa_fixed_dh(3), dss_fixed_dh(4),
rsa_ephemeral_dh_RESERVED(5), dss_ephemeral_dh_RESERVED(6), rsa_ephemeral_dh_RESERVED(5), dss_ephemeral_dh_RESERVED(6),
fortezza_dms_RESERVED(20), (255) fortezza_dms_RESERVED(20), (255)
} ClientCertificateType; } ClientCertificateType;
opaque DistinguishedName<1..2^16-1>; opaque DistinguishedName<1..2^16-1>;
struct { struct {
ClientCertificateType certificate_types<1..2^8-1>; ClientCertificateType certificate_types<1..2^8-1>;
SignatureAndHashAlgorithm SignatureAndHashAlgorithm
supported_signature_algorithms<2^16-1>; supported_signature_algorithms<2^16-1>;
DistinguishedName certificate_authorities<0..2^16-1>; DistinguishedName certificate_authorities<0..2^16-1>;
} CertificateRequest; } CertificateRequest;
certificate_types certificate_types
A list of the types of certificate types which the client may A list of the types of certificate types that the client may
offer. offer.
rsa_sign a certificate containing an RSA key rsa_sign a certificate containing an RSA key
dss_sign a certificate containing a DSA key dss_sign a certificate containing a DSA key
rsa_fixed_dh a certificate containing a static DH key. rsa_fixed_dh a certificate containing a static DH key.
dss_fixed_dh a certificate containing a static DH key dss_fixed_dh a certificate containing a static DH key
supported_signature_algorithms supported_signature_algorithms
A list of the hash/signature algorithm pairs that the server is A list of the hash/signature algorithm pairs that the server is
able to verify, listed in descending order of preference. able to verify, listed in descending order of preference.
certificate_authorities certificate_authorities
A list of the distinguished names [X501] of acceptable A list of the distinguished names [X501] of acceptable
certificate_authorities, represented in DER-encoded format. These certificate_authorities, represented in DER-encoded format. These
distinguished names may specify a desired distinguished name for a distinguished names may specify a desired distinguished name for a
root CA or for a subordinate CA; thus, this message can be used root CA or for a subordinate CA; thus, this message can be used to
both to describe known roots and a desired authorization space. If describe known roots as well as a desired authorization space. If
the certificate_authorities list is empty then the client MAY send the certificate_authorities list is empty, then the client MAY
any certificate of the appropriate ClientCertificateType, unless send any certificate of the appropriate ClientCertificateType,
there is some external arrangement to the contrary. unless there is some external arrangement to the contrary.
The interaction of the certificate_types and The interaction of the certificate_types and
supported_signature_algorithms fields is somewhat complicated. supported_signature_algorithms fields is somewhat complicated.
certificate_types has been present in TLS since SSLv3, but was certificate_types has been present in TLS since SSLv3, but was
somewhat underspecified. Much of its functionality is superseded by somewhat underspecified. Much of its functionality is superseded by
supported_signature_algorithms. The following rules apply: supported_signature_algorithms. The following rules apply:
- Any certificates provided by the client MUST be signed using a - Any certificates provided by the client MUST be signed using a
hash/signature algorithm pair found in hash/signature algorithm pair found in
supported_signature_algorithms. supported_signature_algorithms.
- The end-entity certificate provided by the client MUST contain a - The end-entity certificate provided by the client MUST contain a
key which is compatible with certificate_types. If the key is a key that is compatible with certificate_types. If the key is a
signature key, it MUST be usable with some hash/signature signature key, it MUST be usable with some hash/signature
algorithm pair in supported_signature_algorithms. algorithm pair in supported_signature_algorithms.
- For historical reasons, the names of some client certificate types - For historical reasons, the names of some client certificate types
include the algorithm used to sign the certificate. For example, include the algorithm used to sign the certificate. For example,
in earlier versions of TLS, rsa_fixed_dh meant a certificate in earlier versions of TLS, rsa_fixed_dh meant a certificate
signed with RSA and containing a static DH key. In TLS 1.2, this signed with RSA and containing a static DH key. In TLS 1.2, this
functionality has been obsoleted by the functionality has been obsoleted by the
supported_signature_algorithms, and the certificate type no longer supported_signature_algorithms, and the certificate type no longer
restricts the algorithm used to sign the certificate. For restricts the algorithm used to sign the certificate. For
example, if the server sends dss_fixed_dh certificate type and example, if the server sends dss_fixed_dh certificate type and
{{sha1, dsa}, {sha1, rsa}} signature types, the client MAY reply {{sha1, dsa}, {sha1, rsa}} signature types, the client MAY reply
with a certificate containing a static DH key, signed with RSA- with a certificate containing a static DH key, signed with RSA-
SHA1. SHA1.
New ClientCertificateType values are assigned by IANA as described in New ClientCertificateType values are assigned by IANA as described in
Section 12. Section 12.
Note: Values listed as RESERVED may not be used. They were used in Note: Values listed as RESERVED may not be used. They were used in
SSLv3. SSLv3.
Note: It is a fatal handshake_failure alert for an anonymous server Note: It is a fatal handshake_failure alert for an anonymous server
to request client authentication. to request client authentication.
7.4.5 Server Hello Done 7.4.5. Server Hello Done
When this message will be sent: When this message will be sent:
The ServerHelloDone message is sent by the server to indicate the The ServerHelloDone message is sent by the server to indicate the
end of the ServerHello and associated messages. After sending this end of the ServerHello and associated messages. After sending
message, the server will wait for a client response. this message, the server will wait for a client response.
Meaning of this message: Meaning of this message:
This message means that the server is done sending messages to This message means that the server is done sending messages to
support the key exchange, and the client can proceed with its support the key exchange, and the client can proceed with its
phase of the key exchange. phase of the key exchange.
Upon receipt of the ServerHelloDone message, the client SHOULD Upon receipt of the ServerHelloDone message, the client SHOULD
verify that the server provided a valid certificate, if required, verify that the server provided a valid certificate, if required,
and check that the server hello parameters are acceptable. and check that the server hello parameters are acceptable.
Structure of this message: Structure of this message:
struct { } ServerHelloDone; struct { } ServerHelloDone;
7.4.6. Client Certificate 7.4.6. Client Certificate
When this message will be sent: When this message will be sent:
This is the first message the client can send after receiving a This is the first message the client can send after receiving a
server hello done message. This message is only sent if the server ServerHelloDone message. This message is only sent if the server
requests a certificate. If no suitable certificate is available, requests a certificate. If no suitable certificate is available,
the client MUST send a certificate message containing no the client MUST send a certificate message containing no
certificates. That is, the certificate_list structure has a length certificates. That is, the certificate_list structure has a
of zero. If the client does not send any certificates, the server length of zero. If the client does not send any certificates, the
MAY at its discretion either continue the handshake without client server MAY at its discretion either continue the handshake without
authentication, or respond with a fatal handshake_failure alert. client authentication, or respond with a fatal handshake_failure
Also, if some aspect of the certificate chain was unacceptable alert. Also, if some aspect of the certificate chain was
(e.g., it was not signed by a known, trusted CA), the server MAY unacceptable (e.g., it was not signed by a known, trusted CA), the
at its discretion either continue the handshake (considering the server MAY at its discretion either continue the handshake
client unauthenticated) or send a fatal alert. (considering the client unauthenticated) or send a fatal alert.
Client certificates are sent using the Certificate structure Client certificates are sent using the Certificate structure
defined in Section 7.4.2. defined in Section 7.4.2.
Meaning of this message: Meaning of this message:
This message conveys the client's certificate chain to the server; This message conveys the client's certificate chain to the server;
the server will use it when verifying the CertificateVerify the server will use it when verifying the CertificateVerify
message (when the client authentication is based on signing) or message (when the client authentication is based on signing) or
calculating the premaster secret (for non-ephemeral Diffie- calculating the premaster secret (for non-ephemeral Diffie-
Hellman). The certificate MUST be appropriate for the negotiated Hellman). The certificate MUST be appropriate for the negotiated
cipher suite's key exchange algorithm, and any negotiated cipher suite's key exchange algorithm, and any negotiated
extensions. extensions.
In particular: In particular:
- The certificate type MUST be X.509v3, unless explicitly negotiated - The certificate type MUST be X.509v3, unless explicitly negotiated
otherwise (e.g. [TLSPGP]). otherwise (e.g., [TLSPGP]).
- The end-entity certificate's public key (and associated - The end-entity certificate's public key (and associated
restrictions) has to be compatible with the certificate types restrictions) has to be compatible with the certificate types
listed in CertificateRequest: listed in CertificateRequest:
Client Cert. Type Certificate Key Type Client Cert. Type Certificate Key Type
rsa_sign RSA public key; the certificate MUST allow rsa_sign RSA public key; the certificate MUST allow the
the key to be used for signing with the key to be used for signing with the signature
signature scheme and hash algorithm that scheme and hash algorithm that will be
will be employed in the certificate verify employed in the certificate verify message.
message.
dss_sign DSA public key; the certificate MUST allow dss_sign DSA public key; the certificate MUST allow the
the key to be used for signing with the key to be used for signing with the hash
hash algorithm that will be employed in algorithm that will be employed in the
the certificate verify message. certificate verify message.
ecdsa_sign ECDSA-capable public key; the certificate ecdsa_sign ECDSA-capable public key; the certificate MUST
MUST allow the key to be used for signing allow the key to be used for signing with the
with the hash algorithm that will be hash algorithm that will be employed in the
employed in the certificate verify certificate verify message; the public key
message; the public key MUST use a MUST use a curve and point format supported by
curve and point format supported by the the server.
server.
rsa_fixed_dh Diffie-Hellman public key; MUST use rsa_fixed_dh Diffie-Hellman public key; MUST use the same
dss_fixed_dh the same parameters as server's key. dss_fixed_dh parameters as server's key.
rsa_fixed_ecdh ECDH-capable public key; MUST use the rsa_fixed_ecdh ECDH-capable public key; MUST use the
ecdsa_fixed_ecdh same curve as the server's key, and ecdsa_fixed_ecdh same curve as the server's key, and MUST use a
MUST use a point format supported by point format supported by the server.
the server.
- If the certificate_authorities list in the certificate request - If the certificate_authorities list in the certificate request
message was non-empty, one of the certificates in the certificate message was non-empty, one of the certificates in the certificate
chain SHOULD be issued by one of the listed CAs. chain SHOULD be issued by one of the listed CAs.
- The certificates MUST be signed using an acceptable hash/ - The certificates MUST be signed using an acceptable hash/
signature algorithm pair, as described in Section 7.4.4. Note that signature algorithm pair, as described in Section 7.4.4. Note
this relaxes the constraints on certificate signing algorithms that this relaxes the constraints on certificate-signing
found in prior versions of TLS. algorithms found in prior versions of TLS.
Note that as with the server certificate, there are certificates that Note that, as with the server certificate, there are certificates
use algorithms/algorithm combinations that cannot be currently used that use algorithms/algorithm combinations that cannot be currently
with TLS. used with TLS.
7.4.7. Client Key Exchange Message 7.4.7. Client Key Exchange Message
When this message will be sent: When this message will be sent:
This message is always sent by the client. It MUST immediately This message is always sent by the client. It MUST immediately
follow the client certificate message, if it is sent. Otherwise it follow the client certificate message, if it is sent. Otherwise,
MUST be the first message sent by the client after it receives the it MUST be the first message sent by the client after it receives
server hello done message. the ServerHelloDone message.
Meaning of this message: Meaning of this message:
With this message, the premaster secret is set, either through With this message, the premaster secret is set, either by direct
direct transmission of the RSA-encrypted secret, or by the transmission of the RSA-encrypted secret or by the transmission of
transmission of Diffie-Hellman parameters that will allow each Diffie-Hellman parameters that will allow each side to agree upon
side to agree upon the same premaster secret. the same premaster secret.
When the client is using an ephemeral Diffie-Hellman exponent, When the client is using an ephemeral Diffie-Hellman exponent,
then this message contains the client's Diffie-Hellman public then this message contains the client's Diffie-Hellman public
value. If the client is sending a certificate containing a static value. If the client is sending a certificate containing a static
DH exponent (i.e., it is doing fixed_dh client authentication) DH exponent (i.e., it is doing fixed_dh client authentication),
then this message MUST be sent but MUST be empty. then this message MUST be sent but MUST be empty.
Structure of this message: Structure of this message:
The choice of messages depends on which key exchange method has The choice of messages depends on which key exchange method has
been selected. See Section 7.4.3 for the KeyExchangeAlgorithm been selected. See Section 7.4.3 for the KeyExchangeAlgorithm
definition. definition.
struct { struct {
select (KeyExchangeAlgorithm) { select (KeyExchangeAlgorithm) {
case rsa: case rsa:
EncryptedPreMasterSecret; EncryptedPreMasterSecret;
case dhe_dss: case dhe_dss:
case dhe_rsa: case dhe_rsa:
case dh_dss: case dh_dss:
case dh_rsa: case dh_rsa:
case dh_anon: case dh_anon:
ClientDiffieHellmanPublic; ClientDiffieHellmanPublic;
} exchange_keys; } exchange_keys;
} ClientKeyExchange; } ClientKeyExchange;
7.4.7.1. RSA Encrypted Premaster Secret Message 7.4.7.1. RSA-Encrypted Premaster Secret Message
Meaning of this message: Meaning of this message:
If RSA is being used for key agreement and authentication, the If RSA is being used for key agreement and authentication, the
client generates a 48-byte premaster secret, encrypts it using the client generates a 48-byte premaster secret, encrypts it using the
public key from the server's certificate and sends the result in public key from the server's certificate, and sends the result in
an encrypted premaster secret message. This structure is a variant an encrypted premaster secret message. This structure is a
of the ClientKeyExchange message and is not a message in itself. variant of the ClientKeyExchange message and is not a message in
itself.
Structure of this message: Structure of this message:
struct { struct {
ProtocolVersion client_version; ProtocolVersion client_version;
opaque random[46]; opaque random[46];
} PreMasterSecret; } PreMasterSecret;
client_version client_version
The latest (newest) version supported by the client. This is The latest (newest) version supported by the client. This is
used to detect version roll-back attacks. used to detect version rollback attacks.
random random
46 securely-generated random bytes. 46 securely-generated random bytes.
struct { struct {
public-key-encrypted PreMasterSecret pre_master_secret; public-key-encrypted PreMasterSecret pre_master_secret;
} EncryptedPreMasterSecret; } EncryptedPreMasterSecret;
pre_master_secret pre_master_secret
This random value is generated by the client and is used to This random value is generated by the client and is used to
generate the master secret, as specified in Section 8.1. generate the master secret, as specified in Section 8.1.
Note: The version number in the PreMasterSecret is the version Note: The version number in the PreMasterSecret is the version
offered by the client in the ClientHello.client_version, not the offered by the client in the ClientHello.client_version, not the
version negotiated for the connection. This feature is designed to version negotiated for the connection. This feature is designed to
prevent rollback attacks. Unfortunately, some old implementations prevent rollback attacks. Unfortunately, some old implementations
use the negotiated version instead and therefore checking the version use the negotiated version instead, and therefore checking the
number may lead to failure to interoperate with such incorrect client version number may lead to failure to interoperate with such
implementations. incorrect client implementations.
Client implementations MUST always send the correct version number in Client implementations MUST always send the correct version number in
PreMasterSecret. If ClientHello.client_version is TLS 1.1 or higher, PreMasterSecret. If ClientHello.client_version is TLS 1.1 or higher,
server implementations MUST check the version number as described in server implementations MUST check the version number as described in
the note below. If the version number is TLS 1.0 or earlier, server the note below. If the version number is TLS 1.0 or earlier, server
implementations SHOULD check the version number, but MAY have a implementations SHOULD check the version number, but MAY have a
configuration option to disable the check. Note that if the check configuration option to disable the check. Note that if the check
fails, the PreMasterSecret SHOULD be randomized as described below. fails, the PreMasterSecret SHOULD be randomized as described below.
Note: Attacks discovered by Bleichenbacher [BLEI] and Klima et al. Note: Attacks discovered by Bleichenbacher [BLEI] and Klima et al.
[KPR03] can be used to attack a TLS server that reveals whether a [KPR03] can be used to attack a TLS server that reveals whether a
particular message, when decrypted, is properly PKCS#1 formatted, particular message, when decrypted, is properly PKCS#1 formatted,
contains a valid PreMasterSecret structure, or has the correct contains a valid PreMasterSecret structure, or has the correct
version number. version number.
The best way to avoid these vulnerabilities is to treat incorrectly As described by Klima [KPR03], these vulnerabilities can be avoided
formatted messages in a manner indistinguishable from correctly by treating incorrectly formatted message blocks and/or mismatched
formatted RSA blocks. In other words: version numbers in a manner indistinguishable from correctly
formatted RSA blocks. In other words:
1. Generate a string R of 46 random bytes 1. Generate a string R of 46 random bytes
2. Decrypt the message to recover the plaintext M 2. Decrypt the message to recover the plaintext M
3. If the PKCS#1 padding is not correct, or the length of 3. If the PKCS#1 padding is not correct, or the length of message
message M is not exactly 48 bytes: M is not exactly 48 bytes:
premaster secret = ClientHello.client_version || R pre_master_secret = ClientHello.client_version || R
else If ClientHello.client_version <= TLS 1.0, and else If ClientHello.client_version <= TLS 1.0, and version
version number check is explicitly disabled: number check is explicitly disabled:
premaster secret = M pre_master_secret = M
else: else:
premaster secret = ClientHello.client_version || M[2..47] pre_master_secret = ClientHello.client_version || M[2..47]
Note that explicitly constructing the premaster_secret with the Note that explicitly constructing the pre_master_secret with the
ClientHello.client_version produces an invalid master_secret if the ClientHello.client_version produces an invalid master_secret if the
client has sent the wrong version in the original premaster_secret. client has sent the wrong version in the original pre_master_secret.
An alternative approach is to treat a version number mismatch as a
PKCS-1 formatting error and randomize the premaster secret
completely:
1. Generate a string R of 48 random bytes
2. Decrypt the message to recover the plaintext M
3. If the PKCS#1 padding is not correct, or the length of message
M is not exactly 48 bytes:
pre_master_secret = R
else If ClientHello.client_version <= TLS 1.0, and version
number check is explicitly disabled:
premaster secret = M
else If M[0..1] != ClientHello.client_version:
premaster secret = R
else:
premaster secret = M
Although no practical attacks against this construction are known,
Klima et al. [KPR03] describe some theoretical attacks, and therefore
the first construction described is RECOMMENDED.
In any case, a TLS server MUST NOT generate an alert if processing an In any case, a TLS server MUST NOT generate an alert if processing an
RSA-encrypted premaster secret message fails, or the version number RSA-encrypted premaster secret message fails, or the version number
is not as expected. Instead, it MUST continue the handshake with a is not as expected. Instead, it MUST continue the handshake with a
randomly generated premaster secret. It may be useful to log the randomly generated premaster secret. It may be useful to log the
real cause of failure for troubleshooting purposes; however, care real cause of failure for troubleshooting purposes; however, care
must be taken to avoid leaking the information to an attacker must be taken to avoid leaking the information to an attacker
(through, e.g., timing, log files, or other channels.) (through, e.g., timing, log files, or other channels.)
The RSAES-OAEP encryption scheme defined in [PKCS1] is more secure The RSAES-OAEP encryption scheme defined in [PKCS1] is more secure
against the Bleichenbacher attack. However, for maximal compatibility against the Bleichenbacher attack. However, for maximal
with earlier versions of TLS, this specification uses the RSAES- compatibility with earlier versions of TLS, this specification uses
PKCS1-v1_5 scheme. No variants of the Bleichenbacher attack are known the RSAES-PKCS1-v1_5 scheme. No variants of the Bleichenbacher
to exist provided that the above recommendations are followed. attack are known to exist provided that the above recommendations are
followed.
Implementation Note: Public-key-encrypted data is represented as an Implementation note: Public-key-encrypted data is represented as an
opaque vector <0..2^16-1> (see Section 4.7). Thus, the RSA-encrypted opaque vector <0..2^16-1> (see Section 4.7). Thus, the RSA-encrypted
PreMasterSecret in a ClientKeyExchange is preceded by two length PreMasterSecret in a ClientKeyExchange is preceded by two length
bytes. These bytes are redundant in the case of RSA because the bytes. These bytes are redundant in the case of RSA because the
EncryptedPreMasterSecret is the only data in the ClientKeyExchange EncryptedPreMasterSecret is the only data in the ClientKeyExchange
and its length can therefore be unambiguously determined. The SSLv3 and its length can therefore be unambiguously determined. The SSLv3
specification was not clear about the encoding of public-key- specification was not clear about the encoding of public-key-
encrypted data, and therefore many SSLv3 implementations do not encrypted data, and therefore many SSLv3 implementations do not
include the length bytes, encoding the RSA encrypted data directly in include the length bytes -- they encode the RSA-encrypted data
the ClientKeyExchange message. directly in the ClientKeyExchange message.
This specification requires correct encoding of the This specification requires correct encoding of the
EncryptedPreMasterSecret complete with length bytes. The resulting EncryptedPreMasterSecret complete with length bytes. The resulting
PDU is incompatible with many SSLv3 implementations. Implementors PDU is incompatible with many SSLv3 implementations. Implementors
upgrading from SSLv3 MUST modify their implementations to generate upgrading from SSLv3 MUST modify their implementations to generate
and accept the correct encoding. Implementors who wish to be and accept the correct encoding. Implementors who wish to be
compatible with both SSLv3 and TLS should make their implementation's compatible with both SSLv3 and TLS should make their implementation's
behavior dependent on the protocol version. behavior dependent on the protocol version.
Implementation Note: It is now known that remote timing-based attacks Implementation note: It is now known that remote timing-based attacks
on TLS are possible, at least when the client and server are on the on TLS are possible, at least when the client and server are on the
same LAN. Accordingly, implementations that use static RSA keys MUST same LAN. Accordingly, implementations that use static RSA keys MUST
use RSA blinding or some other anti-timing technique, as described in use RSA blinding or some other anti-timing technique, as described in
[TIMING]. [TIMING].
7.4.7.2. Client Diffie-Hellman Public Value 7.4.7.2. Client Diffie-Hellman Public Value
Meaning of this message: Meaning of this message:
This structure conveys the client's Diffie-Hellman public value This structure conveys the client's Diffie-Hellman public value
(Yc) if it was not already included in the client's certificate. (Yc) if it was not already included in the client's certificate.
The encoding used for Yc is determined by the enumerated The encoding used for Yc is determined by the enumerated
PublicValueEncoding. This structure is a variant of the client key PublicValueEncoding. This structure is a variant of the client
exchange message, and not a message in itself. key exchange message, and not a message in itself.
Structure of this message: Structure of this message:
enum { implicit, explicit } PublicValueEncoding; enum { implicit, explicit } PublicValueEncoding;
implicit implicit
If the client has sent a certificate which contains a suitable If the client has sent a certificate which contains a suitable
Diffie-Hellman key (for fixed_dh client authentication) then Yc Diffie-Hellman key (for fixed_dh client authentication), then
is implicit and does not need to be sent again. In this case, Yc is implicit and does not need to be sent again. In this
the client key exchange message will be sent, but it MUST be case, the client key exchange message will be sent, but it MUST
empty. be empty.
explicit explicit
Yc needs to be sent. Yc needs to be sent.
struct { struct {
select (PublicValueEncoding) { select (PublicValueEncoding) {
case implicit: struct { }; case implicit: struct { };
case explicit: opaque dh_Yc<1..2^16-1>; case explicit: opaque dh_Yc<1..2^16-1>;
} dh_public; } dh_public;
} ClientDiffieHellmanPublic; } ClientDiffieHellmanPublic;
dh_Yc dh_Yc
The client's Diffie-Hellman public value (Yc). The client's Diffie-Hellman public value (Yc).
7.4.8. Certificate verify 7.4.8. Certificate Verify
When this message will be sent: When this message will be sent:
This message is used to provide explicit verification of a client This message is used to provide explicit verification of a client
certificate. This message is only sent following a client certificate. This message is only sent following a client
certificate that has signing capability (i.e. all certificates certificate that has signing capability (i.e., all certificates
except those containing fixed Diffie-Hellman parameters). When except those containing fixed Diffie-Hellman parameters). When
sent, it MUST immediately follow the client key exchange message. sent, it MUST immediately follow the client key exchange message.
Structure of this message: Structure of this message:
struct { struct {
digitally-signed struct { digitally-signed struct {
opaque handshake_messages[handshake_messages_length]; opaque handshake_messages[handshake_messages_length];
} }
} CertificateVerify; } CertificateVerify;
Here handshake_messages refers to all handshake messages sent or Here handshake_messages refers to all handshake messages sent or
received starting at client hello up to but not including this received, starting at client hello and up to, but not including,
message, including the type and length fields of the handshake this message, including the type and length fields of the
messages. This is the concatenation of all the Handshake handshake messages. This is the concatenation of all the
structures as defined in 7.4 exchanged thus far. Note that this Handshake structures (as defined in Section 7.4) exchanged thus
requires both sides to either buffer the messages or compute far. Note that this requires both sides to either buffer the
running hashes for all potential hash algorithms up to the time of messages or compute running hashes for all potential hash
the CertificateVerify computation. Servers can minimize this algorithms up to the time of the CertificateVerify computation.
computation cost by offering a restricted set of digest algorithms Servers can minimize this computation cost by offering a
in the CertificateRequest message. restricted set of digest algorithms in the CertificateRequest
message.
The hash and signature algorithms used in the signature MUST be The hash and signature algorithms used in the signature MUST be
one of those present in the supported_signature_algorithms field one of those present in the supported_signature_algorithms field
of the CertificateRequest message. In addition, the hash and of the CertificateRequest message. In addition, the hash and
signature algorithms MUST be compatible with the key in the signature algorithms MUST be compatible with the key in the
client's end-entity certificate. RSA keys MAY be used with any client's end-entity certificate. RSA keys MAY be used with any
permitted hash algorithm, subject to restrictions in the permitted hash algorithm, subject to restrictions in the
certificate, if any. certificate, if any.
Because DSA signatures do not contain any secure indication of Because DSA signatures do not contain any secure indication of
hash algorithm, there is a risk of hash substitution if multiple hash algorithm, there is a risk of hash substitution if multiple
hashes may be used with any key. Currently, DSA [DSS] may only be hashes may be used with any key. Currently, DSA [DSS] may only be
used with SHA-1. Future revisions of DSS [DSS-3] are expected to used with SHA-1. Future revisions of DSS [DSS-3] are expected to
allow the use of other digest algorithms with DSA, as well as allow the use of other digest algorithms with DSA, as well as
guidance as to which digest algorithms should be used with each guidance as to which digest algorithms should be used with each
key size. In addition, future revisions of [PKIX] may specify key size. In addition, future revisions of [PKIX] may specify
mechanisms for certificates to indicate which digest algorithms mechanisms for certificates to indicate which digest algorithms
are to be used with DSA. are to be used with DSA.
7.4.9. Finished 7.4.9. Finished
When this message will be sent: When this message will be sent:
A Finished message is always sent immediately after a change A Finished message is always sent immediately after a change
cipher spec message to verify that the key exchange and cipher spec message to verify that the key exchange and
authentication processes were successful. It is essential that a authentication processes were successful. It is essential that a
change cipher spec message be received between the other handshake change cipher spec message be received between the other handshake
messages and the Finished message. messages and the Finished message.
Meaning of this message: Meaning of this message:
The finished message is the first one protected with the just The Finished message is the first one protected with the just
negotiated algorithms, keys, and secrets. Recipients of finished negotiated algorithms, keys, and secrets. Recipients of Finished
messages MUST verify that the contents are correct. Once a side messages MUST verify that the contents are correct. Once a side
has sent its Finished message and received and validated the has sent its Finished message and received and validated the
Finished message from its peer, it may begin to send and receive Finished message from its peer, it may begin to send and receive
application data over the connection. application data over the connection.
Structure of this message: Structure of this message:
struct { struct {
opaque verify_data[verify_data_length]; opaque verify_data[verify_data_length];
} Finished; } Finished;
verify_data verify_data
PRF(master_secret, finished_label, Hash(handshake_messages)) PRF(master_secret, finished_label, Hash(handshake_messages))
[0..verify_data_length-1]; [0..verify_data_length-1];
finished_label finished_label
For Finished messages sent by the client, the string "client For Finished messages sent by the client, the string
finished". For Finished messages sent by the server, the string "client finished". For Finished messages sent by the server,
"server finished". the string "server finished".
Hash denotes a Hash of the handshake messages. For the PRF defined Hash denotes a Hash of the handshake messages. For the PRF
in Section 5, the Hash MUST be the Hash used as the basis for the defined in Section 5, the Hash MUST be the Hash used as the basis
PRF. Any cipher suite which defines a different PRF MUST also for the PRF. Any cipher suite which defines a different PRF MUST
define the Hash to use in the Finished computation. also define the Hash to use in the Finished computation.
In previous versions of TLS, the verify_data was always 12 octets In previous versions of TLS, the verify_data was always 12 octets
long. In the current version of TLS, it depends on the cipher long. In the current version of TLS, it depends on the cipher
suite. Any cipher suite which does not explicitly specify suite. Any cipher suite which does not explicitly specify
verify_data_length has a verify_data_length equal to 12. This verify_data_length has a verify_data_length equal to 12. This
includes all existing cipher suites. Note that this includes all existing cipher suites. Note that this
representation has the same encoding as with previous versions. representation has the same encoding as with previous versions.
Future cipher suites MAY specify other lengths but such length Future cipher suites MAY specify other lengths but such length
MUST be at least 12 bytes. MUST be at least 12 bytes.
handshake_messages handshake_messages
All of the data from all messages in this handshake (not All of the data from all messages in this handshake (not
including any HelloRequest messages) up to but not including including any HelloRequest messages) up to, but not including,
this message. This is only data visible at the handshake layer this message. This is only data visible at the handshake layer
and does not include record layer headers. This is the and does not include record layer headers. This is the
concatenation of all the Handshake structures as defined in concatenation of all the Handshake structures as defined in
7.4, exchanged thus far. Section 7.4, exchanged thus far.
It is a fatal error if a finished message is not preceded by a It is a fatal error if a Finished message is not preceded by a
ChangeCipherSpec message at the appropriate point in the handshake. ChangeCipherSpec message at the appropriate point in the handshake.
The value handshake_messages includes all handshake messages starting The value handshake_messages includes all handshake messages starting
at ClientHello up to, but not including, this Finished message. This at ClientHello up to, but not including, this Finished message. This
may be different from handshake_messages in Section 7.4.8 because it may be different from handshake_messages in Section 7.4.8 because it
would include the CertificateVerify message (if sent). Also, the would include the CertificateVerify message (if sent). Also, the
handshake_messages for the Finished message sent by the client will handshake_messages for the Finished message sent by the client will
be different from that for the Finished message sent by the server, be different from that for the Finished message sent by the server,
because the one that is sent second will include the prior one. because the one that is sent second will include the prior one.
Note: ChangeCipherSpec messages, alerts, and any other record types Note: ChangeCipherSpec messages, alerts, and any other record types
are not handshake messages and are not included in the hash are not handshake messages and are not included in the hash
computations. Also, HelloRequest messages are omitted from handshake computations. Also, HelloRequest messages are omitted from handshake
hashes. hashes.
8. Cryptographic Computations 8. Cryptographic Computations
In order to begin connection protection, the TLS Record Protocol In order to begin connection protection, the TLS Record Protocol
requires specification of a suite of algorithms, a master secret, and requires specification of a suite of algorithms, a master secret, and
the client and server random values. The authentication, encryption, the client and server random values. The authentication, encryption,
and MAC algorithms are determined by the cipher_suite selected by the and MAC algorithms are determined by the cipher_suite selected by the
server and revealed in the server hello message. The compression server and revealed in the ServerHello message. The compression
algorithm is negotiated in the hello messages, and the random values algorithm is negotiated in the hello messages, and the random values
are exchanged in the hello messages. All that remains is to calculate are exchanged in the hello messages. All that remains is to
the master secret. calculate the master secret.
8.1. Computing the Master Secret 8.1. Computing the Master Secret
For all key exchange methods, the same algorithm is used to convert For all key exchange methods, the same algorithm is used to convert
the pre_master_secret into the master_secret. The pre_master_secret the pre_master_secret into the master_secret. The pre_master_secret
should be deleted from memory once the master_secret has been should be deleted from memory once the master_secret has been
computed. computed.
master_secret = PRF(pre_master_secret, "master secret", master_secret = PRF(pre_master_secret, "master secret",
ClientHello.random + ServerHello.random) ClientHello.random + ServerHello.random)
[0..47]; [0..47];
The master secret is always exactly 48 bytes in length. The length of The master secret is always exactly 48 bytes in length. The length
the premaster secret will vary depending on key exchange method. of the premaster secret will vary depending on key exchange method.
8.1.1. RSA 8.1.1. RSA
When RSA is used for server authentication and key exchange, a When RSA is used for server authentication and key exchange, a 48-
48-byte pre_master_secret is generated by the client, encrypted under byte pre_master_secret is generated by the client, encrypted under
the server's public key, and sent to the server. The server uses its the server's public key, and sent to the server. The server uses its
private key to decrypt the pre_master_secret. Both parties then private key to decrypt the pre_master_secret. Both parties then
convert the pre_master_secret into the master_secret, as specified convert the pre_master_secret into the master_secret, as specified
above. above.
8.1.2. Diffie-Hellman 8.1.2. Diffie-Hellman
A conventional Diffie-Hellman computation is performed. The A conventional Diffie-Hellman computation is performed. The
negotiated key (Z) is used as the pre_master_secret, and is converted negotiated key (Z) is used as the pre_master_secret, and is converted
into the master_secret, as specified above. Leading bytes of Z that into the master_secret, as specified above. Leading bytes of Z that
contain all zero bits are stripped before it is used as the contain all zero bits are stripped before it is used as the
pre_master_secret. pre_master_secret.
Note: Diffie-Hellman parameters are specified by the server and may Note: Diffie-Hellman parameters are specified by the server and may
be either ephemeral or contained within the server's certificate. be either ephemeral or contained within the server's certificate.
9. Mandatory Cipher Suites 9. Mandatory Cipher Suites
In the absence of an application profile standard specifying In the absence of an application profile standard specifying
otherwise, a TLS compliant application MUST implement the cipher otherwise, a TLS-compliant application MUST implement the cipher
suite TLS_RSA_WITH_AES_128_CBC_SHA (see Appendix A.5 for the suite TLS_RSA_WITH_AES_128_CBC_SHA (see Appendix A.5 for the
definition). definition).
10. Application Data Protocol 10. Application Data Protocol
Application data messages are carried by the Record Layer and are Application data messages are carried by the record layer and are
fragmented, compressed, and encrypted based on the current connection fragmented, compressed, and encrypted based on the current connection
state. The messages are treated as transparent data to the record state. The messages are treated as transparent data to the record
layer. layer.
11. Security Considerations 11. Security Considerations
Security issues are discussed throughout this memo, especially in Security issues are discussed throughout this memo, especially in
Appendices D, E, and F. Appendices D, E, and F.
12. IANA Considerations 12. IANA Considerations
This document uses several registries that were originally created in This document uses several registries that were originally created in
[TLS1.1]. IANA is requested to update (has updated) these to [TLS1.1]. IANA has updated these to reference this document. The
reference this document. The registries and their allocation policies registries and their allocation policies (unchanged from [TLS1.1])
(unchanged from [TLS1.1]) are listed below. are listed below.
- TLS ClientCertificateType Identifiers Registry: Future values in - TLS ClientCertificateType Identifiers Registry: Future values in
the range 0-63 (decimal) inclusive are assigned via Standards the range 0-63 (decimal) inclusive are assigned via Standards
Action [RFC2434]. Values in the range 64-223 (decimal) inclusive Action [RFC2434]. Values in the range 64-223 (decimal) inclusive
are assigned Specification Required [RFC2434]. Values from 224-255 are assigned via Specification Required [RFC2434]. Values from
(decimal) inclusive are reserved for Private Use [RFC2434]. 224-255 (decimal) inclusive are reserved for Private Use
[RFC2434].
- TLS Cipher Suite Registry: Future values with the first byte in - TLS Cipher Suite Registry: Future values with the first byte in
the range 0-191 (decimal) inclusive are assigned via Standards the range 0-191 (decimal) inclusive are assigned via Standards
Action [RFC2434]. Values with the first byte in the range 192-254 Action [RFC2434]. Values with the first byte in the range 192-254
(decimal) are assigned via Specification Required [RFC2434]. (decimal) are assigned via Specification Required [RFC2434].
Values with the first byte 255 (decimal) are reserved for Private Values with the first byte 255 (decimal) are reserved for Private
Use [RFC2434]. Use [RFC2434].
- This document defines several new HMAC-SHA256 based cipher suites, - This document defines several new HMAC-SHA256-based cipher suites,
whose values (in Appendix A.5) are to be (have been) allocated whose values (in Appendix A.5) have been allocated from the TLS
from the TLS Cipher Suite registry. Cipher Suite registry.
- TLS ContentType Registry: Future values are allocated via - TLS ContentType Registry: Future values are allocated via
Standards Action [RFC2434]. Standards Action [RFC2434].
- TLS Alert Registry: Future values are allocated via Standards - TLS Alert Registry: Future values are allocated via Standards
Action [RFC2434]. Action [RFC2434].
- TLS HandshakeType Registry: Future values are allocated via - TLS HandshakeType Registry: Future values are allocated via
Standards Action [RFC2434]. Standards Action [RFC2434].
This document also uses a registry originally created in [RFC4366]. This document also uses a registry originally created in [RFC4366].
IANA is requested to update (has updated) it to reference this IANA has updated it to reference this document. The registry and its
document. The registry and its allocation policy (unchanged from allocation policy (unchanged from [RFC4366]) is listed below:
[RFC4366]) is listed below:
- TLS ExtensionType Registry: Future values are allocated via IETF - TLS ExtensionType Registry: Future values are allocated via IETF
Consensus [RFC2434]. IANA is requested to update this registry to Consensus [RFC2434]. IANA has updated this registry to include
include the signature_algorithms extension and fill in the the signature_algorithms extension and its corresponding value
appropriate value in Section 7.4.1.4. (see Section 7.4.1.4).
In addition, this document defines two new registries to be In addition, this document defines two new registries to be
maintained by IANA: maintained by IANA:
- TLS SignatureAlgorithm Registry: The registry will be initially - TLS SignatureAlgorithm Registry: The registry has been initially
populated with the values described in Section 7.4.1.4.1. Future populated with the values described in Section 7.4.1.4.1. Future
values in the range 0-63 (decimal) inclusive are assigned via values in the range 0-63 (decimal) inclusive are assigned via
Standards Action [RFC2434]. Values in the range 64-223 (decimal) Standards Action [RFC2434]. Values in the range 64-223 (decimal)
inclusive are assigned via Specification Required [RFC2434]. inclusive are assigned via Specification Required [RFC2434].
Values from 224-255 (decimal) inclusive are reserved for Private Values from 224-255 (decimal) inclusive are reserved for Private
Use [RFC2434]. Use [RFC2434].
- TLS HashAlgorithm Registry: The registry will be initially - TLS HashAlgorithm Registry: The registry has been initially
populated with the values described in Section 7.4.1.4.1. Future populated with the values described in Section 7.4.1.4.1. Future
values in the range 0-63 (decimal) inclusive are assigned via values in the range 0-63 (decimal) inclusive are assigned via
Standards Action [RFC2434]. Values in the range 64-223 (decimal) Standards Action [RFC2434]. Values in the range 64-223 (decimal)
inclusive are assigned via Specification Required [RFC2434]. inclusive are assigned via Specification Required [RFC2434].
Values from 224-255 (decimal) inclusive are reserved for Private Values from 224-255 (decimal) inclusive are reserved for Private
Use [RFC2434]. Use [RFC2434].
This document also uses the TLS Compression Method Identifiers This document also uses the TLS Compression Method Identifiers
Registry, defined in [RFC3749]. IANA is requested to allocate Registry, defined in [RFC3749]. IANA has allocated value 0 for
value 0 for the "null" compression method. the "null" compression method.
Appendix A. Protocol Data Structures and Constant Values Appendix A. Protocol Data Structures and Constant Values
This section describes protocol types and constants. This section describes protocol types and constants.
A.1. Record Layer A.1. Record Layer
struct { struct {
uint8 major; uint8 major;
uint8 minor; uint8 minor;
} ProtocolVersion; } ProtocolVersion;
ProtocolVersion version = { 3, 3 }; /* TLS v1.2*/ ProtocolVersion version = { 3, 3 }; /* TLS v1.2*/
enum { enum {
change_cipher_spec(20), alert(21), handshake(22), change_cipher_spec(20), alert(21), handshake(22),
skipping to change at page 66, line 20 skipping to change at page 69, line 20
uint8 padding_length; uint8 padding_length;
}; };
} GenericBlockCipher; } GenericBlockCipher;
struct { struct {
opaque nonce_explicit[SecurityParameters.record_iv_length]; opaque nonce_explicit[SecurityParameters.record_iv_length];
aead-ciphered struct { aead-ciphered struct {
opaque content[TLSCompressed.length]; opaque content[TLSCompressed.length];
}; };
} GenericAEADCipher; } GenericAEADCipher;
A.2. Change Cipher Specs Message
A.2. Change Cipher Specs Message
struct { struct {
enum { change_cipher_spec(1), (255) } type; enum { change_cipher_spec(1), (255) } type;
} ChangeCipherSpec; } ChangeCipherSpec;
A.3. Alert Messages A.3. Alert Messages
enum { warning(1), fatal(2), (255) } AlertLevel; enum { warning(1), fatal(2), (255) } AlertLevel;
enum { enum {
close_notify(0), close_notify(0),
unexpected_message(10), unexpected_message(10),
bad_record_mac(20), bad_record_mac(20),
decryption_failed_RESERVED(21), decryption_failed_RESERVED(21),
record_overflow(22), record_overflow(22),
decompression_failure(30), decompression_failure(30),
skipping to change at page 67, line 16 skipping to change at page 70, line 17
no_renegotiation(100), no_renegotiation(100),
unsupported_extension(110), /* new */ unsupported_extension(110), /* new */
(255) (255)
} AlertDescription; } AlertDescription;
struct { struct {
AlertLevel level; AlertLevel level;
AlertDescription description; AlertDescription description;
} Alert; } Alert;
A.4. Handshake Protocol A.4. Handshake Protocol
enum { enum {
hello_request(0), client_hello(1), server_hello(2), hello_request(0), client_hello(1), server_hello(2),
certificate(11), server_key_exchange (12), certificate(11), server_key_exchange (12),
certificate_request(13), server_hello_done(14), certificate_request(13), server_hello_done(14),
certificate_verify(15), client_key_exchange(16), certificate_verify(15), client_key_exchange(16),
finished(20) finished(20)
(255) (255)
} HandshakeType; } HandshakeType;
skipping to change at page 67, line 44 skipping to change at page 71, line 5
case certificate: Certificate; case certificate: Certificate;
case server_key_exchange: ServerKeyExchange; case server_key_exchange: ServerKeyExchange;
case certificate_request: CertificateRequest; case certificate_request: CertificateRequest;
case server_hello_done: ServerHelloDone; case server_hello_done: ServerHelloDone;
case certificate_verify: CertificateVerify; case certificate_verify: CertificateVerify;
case client_key_exchange: ClientKeyExchange; case client_key_exchange: ClientKeyExchange;
case finished: Finished; case finished: Finished;
} body; } body;
} Handshake; } Handshake;
A.4.1. Hello Messages A.4.1. Hello Messages
struct { } HelloRequest; struct { } HelloRequest;
struct { struct {
uint32 gmt_unix_time; uint32 gmt_unix_time;
opaque random_bytes[28]; opaque random_bytes[28];
} Random; } Random;
opaque SessionID<0..32>; opaque SessionID<0..32>;
uint8 CipherSuite[2]; uint8 CipherSuite[2];
enum { null(0), (255) } CompressionMethod; enum { null(0), (255) } CompressionMethod;
struct { struct {
ProtocolVersion client_version; ProtocolVersion client_version;
Random random; Random random;
SessionID session_id; SessionID session_id;
skipping to change at page 68, line 42 skipping to change at page 72, line 4
struct {}; struct {};
case true: case true:
Extension extensions<0..2^16-1>; Extension extensions<0..2^16-1>;
}; };
} ServerHello; } ServerHello;
struct { struct {
ExtensionType extension_type; ExtensionType extension_type;
opaque extension_data<0..2^16-1>; opaque extension_data<0..2^16-1>;
} Extension; } Extension;
enum { enum {
signature_algorithms(TBD-BY-IANA), (65535) signature_algorithms(13), (65535)
} ExtensionType; } ExtensionType;
enum{ enum{
none(0), md5(1), sha1(2), sha224(3), sha256(4), sha384(5), none(0), md5(1), sha1(2), sha224(3), sha256(4), sha384(5),
sha512(6), (255) sha512(6), (255)
} HashAlgorithm; } HashAlgorithm;
enum { enum {
anonymous(0), rsa(1), dsa(2), ecdsa(3), (255) anonymous(0), rsa(1), dsa(2), ecdsa(3), (255)
} SignatureAlgorithm; } SignatureAlgorithm;
struct { struct {
HashAlgorithm hash; HashAlgorithm hash;
SignatureAlgorithm signature; SignatureAlgorithm signature;
} SignatureAndHashAlgorithm; } SignatureAndHashAlgorithm;
SignatureAndHashAlgorithm SignatureAndHashAlgorithm
supported_signature_algorithms<2..2^16-1>; supported_signature_algorithms<2..2^16-1>;
A.4.2. Server Authentication and Key Exchange Messages A.4.2. Server Authentication and Key Exchange Messages
opaque ASN.1Cert<2^24-1>; opaque ASN.1Cert<2^24-1>;
struct { struct {
ASN.1Cert certificate_list<0..2^24-1>; ASN.1Cert certificate_list<0..2^24-1>;
} Certificate; } Certificate;
enum { dhe_dss, dhe_rsa, dh_anon, rsa,dh_dss, dh_rsa enum { dhe_dss, dhe_rsa, dh_anon, rsa,dh_dss, dh_rsa
/* may be extended, e.g. for ECDH -- see [TLSECC] */ /* may be extended, e.g., for ECDH -- see [TLSECC] */
} KeyExchangeAlgorithm; } KeyExchangeAlgorithm;
struct { struct {
opaque dh_p<1..2^16-1>; opaque dh_p<1..2^16-1>;
opaque dh_g<1..2^16-1>; opaque dh_g<1..2^16-1>;
opaque dh_Ys<1..2^16-1>; opaque dh_Ys<1..2^16-1>;
} ServerDHParams; /* Ephemeral DH parameters */ } ServerDHParams; /* Ephemeral DH parameters */
struct { struct {
select (KeyExchangeAlgorithm) { select (KeyExchangeAlgorithm) {
case dh_anon: case dh_anon:
ServerDHParams params; ServerDHParams params;
case dhe_dss: case dhe_dss:
case dhe_rsa: case dhe_rsa:
ServerDHParams params; ServerDHParams params;
digitally-signed struct { digitally-signed struct {
opaque client_random[32]; opaque client_random[32];
opaque server_random[32]; opaque server_random[32];
skipping to change at page 69, line 51 skipping to change at page 73, line 21
digitally-signed struct { digitally-signed struct {
opaque client_random[32]; opaque client_random[32];
opaque server_random[32]; opaque server_random[32];
ServerDHParams params; ServerDHParams params;
} signed_params; } signed_params;
case rsa: case rsa:
case dh_dss: case dh_dss:
case dh_rsa: case dh_rsa:
struct {} ; struct {} ;
/* message is omitted for rsa, dh_dss, and dh_rsa */ /* message is omitted for rsa, dh_dss, and dh_rsa */
/* may be extended, e.g. for ECDH -- see [TLSECC] */ /* may be extended, e.g., for ECDH -- see [TLSECC] */
} ServerKeyExchange; } ServerKeyExchange;
enum { enum {
rsa_sign(1), dss_sign(2), rsa_fixed_dh(3), dss_fixed_dh(4), rsa_sign(1), dss_sign(2), rsa_fixed_dh(3), dss_fixed_dh(4),
rsa_ephemeral_dh_RESERVED(5), dss_ephemeral_dh_RESERVED(6), rsa_ephemeral_dh_RESERVED(5), dss_ephemeral_dh_RESERVED(6),
fortezza_dms_RESERVED(20), fortezza_dms_RESERVED(20),
(255) (255)
} ClientCertificateType; } ClientCertificateType;
opaque DistinguishedName<1..2^16-1>; opaque DistinguishedName<1..2^16-1>;
struct { struct {
ClientCertificateType certificate_types<1..2^8-1>; ClientCertificateType certificate_types<1..2^8-1>;
DistinguishedName certificate_authorities<0..2^16-1>; DistinguishedName certificate_authorities<0..2^16-1>;
} CertificateRequest; } CertificateRequest;
struct { } ServerHelloDone; struct { } ServerHelloDone;
A.4.3. Client Authentication and Key Exchange Messages A.4.3. Client Authentication and Key Exchange Messages
struct { struct {
select (KeyExchangeAlgorithm) { select (KeyExchangeAlgorithm) {
case rsa: case rsa:
EncryptedPreMasterSecret; EncryptedPreMasterSecret;
case dhe_dss: case dhe_dss:
case dhe_rsa: case dhe_rsa:
case dh_dss: case dh_dss:
case dh_rsa: case dh_rsa:
case dh_anon: case dh_anon:
skipping to change at page 71, line 14 skipping to change at page 74, line 44
case explicit: opaque DH_Yc<1..2^16-1>; case explicit: opaque DH_Yc<1..2^16-1>;
} dh_public; } dh_public;
} ClientDiffieHellmanPublic; } ClientDiffieHellmanPublic;
struct { struct {
digitally-signed struct { digitally-signed struct {
opaque handshake_messages[handshake_messages_length]; opaque handshake_messages[handshake_messages_length];
} }
} CertificateVerify; } CertificateVerify;
A.4.4. Handshake Finalization Message A.4.4. Handshake Finalization Message
struct { struct {
opaque verify_data[verify_data_length]; opaque verify_data[verify_data_length];
} Finished; } Finished;
A.5. The Cipher Suite A.5. The Cipher Suite
The following values define the cipher suite codes used in the client The following values define the cipher suite codes used in the
hello and server hello messages. ClientHello and ServerHello messages.
A cipher suite defines a cipher specification supported in TLS A cipher suite defines a cipher specification supported in TLS
Version 1.2. Version 1.2.
TLS_NULL_WITH_NULL_NULL is specified and is the initial state of a TLS_NULL_WITH_NULL_NULL is specified and is the initial state of a
TLS connection during the first handshake on that channel, but MUST TLS connection during the first handshake on that channel, but MUST
NOT be negotiated, as it provides no more protection than an NOT be negotiated, as it provides no more protection than an
unsecured connection. unsecured connection.
CipherSuite TLS_NULL_WITH_NULL_NULL = { 0x00,0x00 }; CipherSuite TLS_NULL_WITH_NULL_NULL = { 0x00,0x00 };
The following CipherSuite definitions require that the server provide The following CipherSuite definitions require that the server provide
an RSA certificate that can be used for key exchange. The server may an RSA certificate that can be used for key exchange. The server may
request any signature-capable certificate in the certificate request request any signature-capable certificate in the certificate request
message. message.
CipherSuite TLS_RSA_WITH_NULL_MD5 = { 0x00,0x01 }; CipherSuite TLS_RSA_WITH_NULL_MD5 = { 0x00,0x01 };
CipherSuite TLS_RSA_WITH_NULL_SHA = { 0x00,0x02 }; CipherSuite TLS_RSA_WITH_NULL_SHA = { 0x00,0x02 };
CipherSuite TLS_RSA_WITH_NULL_SHA256 = { 0x00,TBD1 }; CipherSuite TLS_RSA_WITH_NULL_SHA256 = { 0x00,0x3B };
CipherSuite TLS_RSA_WITH_RC4_128_MD5 = { 0x00,0x04 }; CipherSuite TLS_RSA_WITH_RC4_128_MD5 = { 0x00,0x04 };
CipherSuite TLS_RSA_WITH_RC4_128_SHA = { 0x00,0x05 }; CipherSuite TLS_RSA_WITH_RC4_128_SHA = { 0x00,0x05 };
CipherSuite TLS_RSA_WITH_3DES_EDE_CBC_SHA = { 0x00,0x0A }; CipherSuite TLS_RSA_WITH_3DES_EDE_CBC_SHA = { 0x00,0x0A };
CipherSuite TLS_RSA_WITH_AES_128_CBC_SHA = { 0x00,0x2F }; CipherSuite TLS_RSA_WITH_AES_128_CBC_SHA = { 0x00,0x2F };
CipherSuite TLS_RSA_WITH_AES_256_CBC_SHA = { 0x00,0x35 }; CipherSuite TLS_RSA_WITH_AES_256_CBC_SHA = { 0x00,0x35 };
CipherSuite TLS_RSA_WITH_AES_128_CBC_SHA256 = { 0x00,TBD2 }; CipherSuite TLS_RSA_WITH_AES_128_CBC_SHA256 = { 0x00,0x3C };
CipherSuite TLS_RSA_WITH_AES_256_CBC_SHA256 = { 0x00,TBD3 }; CipherSuite TLS_RSA_WITH_AES_256_CBC_SHA256 = { 0x00,0x3D };
The following cipher suite definitions are used for server- The following cipher suite definitions are used for server-
authenticated (and optionally client-authenticated) Diffie-Hellman. authenticated (and optionally client-authenticated) Diffie-Hellman.
DH denotes cipher suites in which the server's certificate contains DH denotes cipher suites in which the server's certificate contains
the Diffie-Hellman parameters signed by the certificate authority the Diffie-Hellman parameters signed by the certificate authority
(CA). DHE denotes ephemeral Diffie-Hellman, where the Diffie-Hellman (CA). DHE denotes ephemeral Diffie-Hellman, where the Diffie-Hellman
parameters are signed by a signature-capable certificate, which has parameters are signed by a signature-capable certificate, which has
been signed by the CA. The signing algorithm used by the server is been signed by the CA. The signing algorithm used by the server is
specified after the DHE component of the CipherSuite name. The server specified after the DHE component of the CipherSuite name. The
can request any signature-capable certificate from the client for server can request any signature-capable certificate from the client
client authentication or it may request a Diffie-Hellman certificate. for client authentication, or it may request a Diffie-Hellman
Any Diffie-Hellman certificate provided by the client must use the certificate. Any Diffie-Hellman certificate provided by the client
parameters (group and generator) described by the server. must use the parameters (group and generator) described by the
server.
CipherSuite TLS_DH_DSS_WITH_3DES_EDE_CBC_SHA = { 0x00,0x0D }; CipherSuite TLS_DH_DSS_WITH_3DES_EDE_CBC_SHA = { 0x00,0x0D };
CipherSuite TLS_DH_RSA_WITH_3DES_EDE_CBC_SHA = { 0x00,0x10 }; CipherSuite TLS_DH_RSA_WITH_3DES_EDE_CBC_SHA = { 0x00,0x10 };
CipherSuite TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA = { 0x00,0x13 }; CipherSuite TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA = { 0x00,0x13 };
CipherSuite TLS_DHE_RSA_WITH_3DES_EDE_CBC_SHA = { 0x00,0x16 }; CipherSuite TLS_DHE_RSA_WITH_3DES_EDE_CBC_SHA = { 0x00,0x16 };
CipherSuite TLS_DH_DSS_WITH_AES_128_CBC_SHA = { 0x00,0x30 }; CipherSuite TLS_DH_DSS_WITH_AES_128_CBC_SHA = { 0x00,0x30 };
CipherSuite TLS_DH_RSA_WITH_AES_128_CBC_SHA = { 0x00,0x31 }; CipherSuite TLS_DH_RSA_WITH_AES_128_CBC_SHA = { 0x00,0x31 };
CipherSuite TLS_DHE_DSS_WITH_AES_128_CBC_SHA = { 0x00,0x32 }; CipherSuite TLS_DHE_DSS_WITH_AES_128_CBC_SHA = { 0x00,0x32 };
CipherSuite TLS_DHE_RSA_WITH_AES_128_CBC_SHA = { 0x00,0x33 }; CipherSuite TLS_DHE_RSA_WITH_AES_128_CBC_SHA = { 0x00,0x33 };
CipherSuite TLS_DH_DSS_WITH_AES_256_CBC_SHA = { 0x00,0x36 }; CipherSuite TLS_DH_DSS_WITH_AES_256_CBC_SHA = { 0x00,0x36 };
CipherSuite TLS_DH_RSA_WITH_AES_256_CBC_SHA = { 0x00,0x37 }; CipherSuite TLS_DH_RSA_WITH_AES_256_CBC_SHA = { 0x00,0x37 };
CipherSuite TLS_DHE_DSS_WITH_AES_256_CBC_SHA = { 0x00,0x38 }; CipherSuite TLS_DHE_DSS_WITH_AES_256_CBC_SHA = { 0x00,0x38 };
CipherSuite TLS_DHE_RSA_WITH_AES_256_CBC_SHA = { 0x00,0x39 }; CipherSuite TLS_DHE_RSA_WITH_AES_256_CBC_SHA = { 0x00,0x39 };
CipherSuite TLS_DH_DSS_WITH_AES_128_CBC_SHA256 = { 0x00,TBD4 }; CipherSuite TLS_DH_DSS_WITH_AES_128_CBC_SHA256 = { 0x00,0x3E };
CipherSuite TLS_DH_RSA_WITH_AES_128_CBC_SHA256 = { 0x00,TBD5 }; CipherSuite TLS_DH_RSA_WITH_AES_128_CBC_SHA256 = { 0x00,0x3F };
CipherSuite TLS_DHE_DSS_WITH_AES_128_CBC_SHA256 = { 0x00,TBD6 }; CipherSuite TLS_DHE_DSS_WITH_AES_128_CBC_SHA256 = { 0x00,0x40 };
CipherSuite TLS_DHE_RSA_WITH_AES_128_CBC_SHA256 = { 0x00,TBD7 }; CipherSuite TLS_DHE_RSA_WITH_AES_128_CBC_SHA256 = { 0x00,0x67 };
CipherSuite TLS_DH_DSS_WITH_AES_256_CBC_SHA256 = { 0x00,TBD8 }; CipherSuite TLS_DH_DSS_WITH_AES_256_CBC_SHA256 = { 0x00,0x68 };
CipherSuite TLS_DH_RSA_WITH_AES_256_CBC_SHA256 = { 0x00,TBD9 }; CipherSuite TLS_DH_RSA_WITH_AES_256_CBC_SHA256 = { 0x00,0x69 };
CipherSuite TLS_DHE_DSS_WITH_AES_256_CBC_SHA256 = { 0x00,TBDA }; CipherSuite TLS_DHE_DSS_WITH_AES_256_CBC_SHA256 = { 0x00,0x6A };
CipherSuite TLS_DHE_RSA_WITH_AES_256_CBC_SHA256 = { 0x00,TBDB }; CipherSuite TLS_DHE_RSA_WITH_AES_256_CBC_SHA256 = { 0x00,0x6B };
The following cipher suites are used for completely anonymous Diffie- The following cipher suites are used for completely anonymous
Hellman communications in which neither party is authenticated. Note Diffie-Hellman communications in which neither party is
that this mode is vulnerable to man-in-the-middle attacks. Using authenticated. Note that this mode is vulnerable to man-in-the-
this mode therefore is of limited use: These cipher suites MUST NOT middle attacks. Using this mode therefore is of limited use: These
be used by TLS 1.2 implementations unless the application layer has cipher suites MUST NOT be used by TLS 1.2 implementations unless the
specifically requested to allow anonymous key exchange. (Anonymous application layer has specifically requested to allow anonymous key
key exchange may sometimes be acceptable, for example, to support exchange. (Anonymous key exchange may sometimes be acceptable, for
opportunistic encryption when no set-up for authentication is in example, to support opportunistic encryption when no set-up for
place, or when TLS is used as part of more complex security protocols authentication is in place, or when TLS is used as part of more
that have other means to ensure authentication.) complex security protocols that have other means to ensure
authentication.)
CipherSuite TLS_DH_anon_WITH_RC4_128_MD5 = { 0x00,0x18 }; CipherSuite TLS_DH_anon_WITH_RC4_128_MD5 = { 0x00,0x18 };
CipherSuite TLS_DH_anon_WITH_3DES_EDE_CBC_SHA = { 0x00,0x1B }; CipherSuite TLS_DH_anon_WITH_3DES_EDE_CBC_SHA = { 0x00,0x1B };
CipherSuite TLS_DH_anon_WITH_AES_128_CBC_SHA = { 0x00,0x34 }; CipherSuite TLS_DH_anon_WITH_AES_128_CBC_SHA = { 0x00,0x34 };
CipherSuite TLS_DH_anon_WITH_AES_256_CBC_SHA = { 0x00,0x3A }; CipherSuite TLS_DH_anon_WITH_AES_256_CBC_SHA = { 0x00,0x3A };
CipherSuite TLS_DH_anon_WITH_AES_128_CBC_SHA256 = { 0x00,TBDC}; CipherSuite TLS_DH_anon_WITH_AES_128_CBC_SHA256 = { 0x00,0x6C };
CipherSuite TLS_DH_anon_WITH_AES_256_CBC_SHA256 = { 0x00,TBDD}; CipherSuite TLS_DH_anon_WITH_AES_256_CBC_SHA256 = { 0x00,0x6D };
Note that using non-anonymous key exchange without actually verifying Note that using non-anonymous key exchange without actually verifying
the key exchange is essentially equivalent to anonymous key exchange, the key exchange is essentially equivalent to anonymous key exchange,
and the same precautions apply. While non-anonymous key exchange and the same precautions apply. While non-anonymous key exchange
will generally involve a higher computational and communicational will generally involve a higher computational and communicational
cost than anonymous key exchange, it may be in the interest of cost than anonymous key exchange, it may be in the interest of
interoperability not to disable non-anonymous key exchange when the interoperability not to disable non-anonymous key exchange when the
application layer is allowing anonymous key exchange. application layer is allowing anonymous key exchange.
New cipher suite values are assigned by IANA as described in Section New cipher suite values have been assigned by IANA as described in
12. Section 12.
Note: The cipher suite values { 0x00, 0x1C } and { 0x00, 0x1D } are Note: The cipher suite values { 0x00, 0x1C } and { 0x00, 0x1D } are
reserved to avoid collision with Fortezza-based cipher suites in SSL reserved to avoid collision with Fortezza-based cipher suites in
3. SSL 3.
A.6. The Security Parameters A.6. The Security Parameters
These security parameters are determined by the TLS Handshake These security parameters are determined by the TLS Handshake
Protocol and provided as parameters to the TLS Record Layer in order Protocol and provided as parameters to the TLS record layer in order
to initialize a connection state. SecurityParameters includes: to initialize a connection state. SecurityParameters includes:
enum { null(0), (255) } CompressionMethod; enum { null(0), (255) } CompressionMethod;
enum { server, client } ConnectionEnd; enum { server, client } ConnectionEnd;
enum { tls_prf_sha256 } PRFAlgorithm; enum { tls_prf_sha256 } PRFAlgorithm;
enum { null, rc4, 3des, aes } enum { null, rc4, 3des, aes } BulkCipherAlgorithm;
BulkCipherAlgorithm;
enum { stream, block, aead } CipherType; enum { stream, block, aead } CipherType;
enum { null, hmac_md5, hmac_sha1, hmac_sha256, hmac_sha384, enum { null, hmac_md5, hmac_sha1, hmac_sha256, hmac_sha384,
hmac_sha512} MACAlgorithm; hmac_sha512} MACAlgorithm;
/* The algorithms specified in CompressionMethod, PRFAlgorithm /* Other values may be added to the algorithms specified in
BulkCipherAlgorithm, and MACAlgorithm may be added to. */ CompressionMethod, PRFAlgorithm, BulkCipherAlgorithm, and
MACAlgorithm. */
struct { struct {
ConnectionEnd entity; ConnectionEnd entity;
PRFAlgorithm prf_algorithm; PRFAlgorithm prf_algorithm;
BulkCipherAlgorithm bulk_cipher_algorithm; BulkCipherAlgorithm bulk_cipher_algorithm;
CipherType cipher_type; CipherType cipher_type;
uint8 enc_key_length; uint8 enc_key_length;
uint8 block_length; uint8 block_length;
uint8 fixed_iv_length; uint8 fixed_iv_length;
uint8 record_iv_length; uint8 record_iv_length;
MACAlgorithm mac_algorithm; MACAlgorithm mac_algorithm;
uint8 mac_length; uint8 mac_length;
uint8 mac_key_length; uint8 mac_key_length;
CompressionMethod compression_algorithm; CompressionMethod compression_algorithm;
opaque master_secret[48]; opaque master_secret[48];
opaque client_random[32]; opaque client_random[32];
opaque server_random[32]; opaque server_random[32];
} SecurityParameters; } SecurityParameters;
A.7. Changes to RFC 4492 A.7. Changes to RFC 4492
RFC 4492 [TLSECC] adds Elliptic Curve cipher suites to TLS. This RFC 4492 [TLSECC] adds Elliptic Curve cipher suites to TLS. This
document changes some of the structures used in that document. This document changes some of the structures used in that document. This
section details the required changes for implementors of both RFC section details the required changes for implementors of both RFC
4492 and TLS 1.2. Implementors of TLS 1.2 who are not implementing 4492 and TLS 1.2. Implementors of TLS 1.2 who are not implementing
RFC 4492 do not need to read this section. RFC 4492 do not need to read this section.
This document adds a "signature_algorithm" field to the digitally- This document adds a "signature_algorithm" field to the digitally-
signed element in order to identify the signature and digest signed element in order to identify the signature and digest
algorithms used to create a signature. This change applies to digital algorithms used to create a signature. This change applies to
signatures formed using ECDSA as well, thus allowing ECDSA signatures digital signatures formed using ECDSA as well, thus allowing ECDSA
to be used with digest algorithms other than SHA-1, provided such use signatures to be used with digest algorithms other than SHA-1,
is compatible with the certificate and any restrictions imposed by provided such use is compatible with the certificate and any
future revisions of [PKIX]. restrictions imposed by future revisions of [PKIX].
As described in Sections 7.4.2 and 7.4.6, the restrictions on the As described in Sections 7.4.2 and 7.4.6, the restrictions on the
signature algorithms used to sign certificates are no longer tied to signature algorithms used to sign certificates are no longer tied to
the cipher suite (when used by the server) or the the cipher suite (when used by the server) or the
ClientCertificateType (when used by the client). Thus, the ClientCertificateType (when used by the client). Thus, the
restrictions on the algorithm used to sign certificates specified in restrictions on the algorithm used to sign certificates specified in
Sections 2 and 3 of RFC 4492 are also relaxed. As in this document Sections 2 and 3 of RFC 4492 are also relaxed. As in this document,
the restrictions on the keys in the end-entity certificate remain. the restrictions on the keys in the end-entity certificate remain.
Appendix B. Glossary Appendix B. Glossary
Advanced Encryption Standard (AES) Advanced Encryption Standard (AES)
AES [AES] is a widely used symmetric encryption algorithm. AES is AES [AES] is a widely used symmetric encryption algorithm. AES is
a block cipher with a 128, 192, or 256 bit keys and a 16 byte a block cipher with a 128-, 192-, or 256-bit keys and a 16-byte
block size. TLS currently only supports the 128 and 256 bit key block size. TLS currently only supports the 128- and 256-bit key
sizes. sizes.
application protocol application protocol
An application protocol is a protocol that normally layers An application protocol is a protocol that normally layers
directly on top of the transport layer (e.g., TCP/IP). Examples directly on top of the transport layer (e.g., TCP/IP). Examples
include HTTP, TELNET, FTP, and SMTP. include HTTP, TELNET, FTP, and SMTP.
asymmetric cipher asymmetric cipher
See public key cryptography. See public key cryptography.
authenticated encryption with additional data (AEAD) authenticated encryption with additional data (AEAD)
A symmetric encryption algorithm that simultaneously provides A symmetric encryption algorithm that simultaneously provides
confidentiality and message integrity. confidentiality and message integrity.
authentication authentication
Authentication is the ability of one entity to determine the Authentication is the ability of one entity to determine the
identity of another entity. identity of another entity.
block cipher block cipher
A block cipher is an algorithm that operates on plaintext in A block cipher is an algorithm that operates on plaintext in
groups of bits, called blocks. 64 bits was, and 128 bits, is a groups of bits, called blocks. 64 bits was, and 128 bits is, a
common block size. common block size.
bulk cipher bulk cipher
A symmetric encryption algorithm used to encrypt large quantities A symmetric encryption algorithm used to encrypt large quantities
of data. of data.
cipher block chaining (CBC) cipher block chaining (CBC)
CBC is a mode in which every plaintext block encrypted with a CBC is a mode in which every plaintext block encrypted with a
block cipher is first exclusive-ORed with the previous ciphertext block cipher is first exclusive-ORed with the previous ciphertext
block (or, in the case of the first block, with the initialization block (or, in the case of the first block, with the initialization
vector). For decryption, every block is first decrypted, then vector). For decryption, every block is first decrypted, then
exclusive-ORed with the previous ciphertext block (or IV). exclusive-ORed with the previous ciphertext block (or IV).
certificate certificate
As part of the X.509 protocol (a.k.a. ISO Authentication As part of the X.509 protocol (a.k.a. ISO Authentication
framework), certificates are assigned by a trusted Certificate framework), certificates are assigned by a trusted Certificate
Authority and provide a strong binding between a party's identity Authority and provide a strong binding between a party's identity
or some other attributes and its public key. or some other attributes and its public key.
client client
The application entity that initiates a TLS connection to a The application entity that initiates a TLS connection to a
server. This may or may not imply that the client initiated the server. This may or may not imply that the client initiated the
underlying transport connection. The primary operational underlying transport connection. The primary operational
difference between the server and client is that the server is difference between the server and client is that the server is
generally authenticated, while the client is only optionally generally authenticated, while the client is only optionally
authenticated. authenticated.
client write key client write key
The key used to encrypt data written by the client. The key used to encrypt data written by the client.
client write MAC key client write MAC key
The secret data used to authenticate data written by the client. The secret data used to authenticate data written by the client.
connection connection
A connection is a transport (in the OSI layering model definition) A connection is a transport (in the OSI layering model definition)
that provides a suitable type of service. For TLS, such that provides a suitable type of service. For TLS, such
connections are peer-to-peer relationships. The connections are connections are peer-to-peer relationships. The connections are
transient. Every connection is associated with one session. transient. Every connection is associated with one session.
Data Encryption Standard Data Encryption Standard
DES [DES] still is a very widely used symmetric encryption DES [DES] still is a very widely used symmetric encryption
algorithm although it is considered as rather weak now. DES is a algorithm although it is considered as rather weak now. DES is a
block cipher with a 56-bit key and an 8-byte block size. Note that block cipher with a 56-bit key and an 8-byte block size. Note
in TLS, for key generation purposes, DES is treated as having an that in TLS, for key generation purposes, DES is treated as having
8-byte key length (64 bits), but it still only provides 56 bits of an 8-byte key length (64 bits), but it still only provides 56 bits
protection. (The low bit of each key byte is presumed to be set to of protection. (The low bit of each key byte is presumed to be
produce odd parity in that key byte.) DES can also be operated in set to produce odd parity in that key byte.) DES can also be
a mode [3DES] where three independent keys and three encryptions operated in a mode [3DES] where three independent keys and three
are used for each block of data; this uses 168 bits of key (24 encryptions are used for each block of data; this uses 168 bits of
bytes in the TLS key generation method) and provides the key (24 bytes in the TLS key generation method) and provides the
equivalent of 112 bits of security. equivalent of 112 bits of security.
Digital Signature Standard (DSS) Digital Signature Standard (DSS)
A standard for digital signing, including the Digital Signing A standard for digital signing, including the Digital Signing
Algorithm, approved by the National Institute of Standards and Algorithm, approved by the National Institute of Standards and
Technology, defined in NIST FIPS PUB 186-2, "Digital Signature Technology, defined in NIST FIPS PUB 186-2, "Digital Signature
Standard", published January 2000 by the U.S. Dept. of Commerce Standard", published January 2000 by the U.S. Department of
[DSS]. A significant update [DSS-3] has been drafted and Commerce [DSS]. A significant update [DSS-3] has been drafted and
published in March 2006. was published in March 2006.
digital signatures digital signatures
Digital signatures utilize public key cryptography and one-way Digital signatures utilize public key cryptography and one-way
hash functions to produce a signature of the data that can be hash functions to produce a signature of the data that can be
authenticated, and is difficult to forge or repudiate. authenticated, and is difficult to forge or repudiate.
handshake handshake An initial negotiation between client and server that
An initial negotiation between client and server that establishes establishes the parameters of their transactions.
the parameters of their transactions.
Initialization Vector (IV) Initialization Vector (IV)
When a block cipher is used in CBC mode, the initialization vector When a block cipher is used in CBC mode, the initialization vector
is exclusive-ORed with the first plaintext block prior to is exclusive-ORed with the first plaintext block prior to
encryption. encryption.
Message Authentication Code (MAC) Message Authentication Code (MAC)
A Message Authentication Code is a one-way hash computed from a A Message Authentication Code is a one-way hash computed from a
message and some secret data. It is difficult to forge without message and some secret data. It is difficult to forge without
knowing the secret data. Its purpose is to detect if the message knowing the secret data. Its purpose is to detect if the message
has been altered. has been altered.
master secret master secret
Secure secret data used for generating encryption keys, MAC Secure secret data used for generating encryption keys, MAC
secrets, and IVs. secrets, and IVs.
MD5 MD5
MD5 [MD5] is a hashing function that converts an arbitrarily long MD5 [MD5] is a hashing function that converts an arbitrarily long
data stream into a hash of fixed size (16 bytes). Due to data stream into a hash of fixed size (16 bytes). Due to
significant progresses in cryptanalysis, at the time of significant progress in cryptanalysis, at the time of publication
publication of this document, MD5 no longer can be considered a of this document, MD5 no longer can be considered a 'secure'
'secure' hashing function. hashing function.
public key cryptography public key cryptography
A class of cryptographic techniques employing two-key ciphers. A class of cryptographic techniques employing two-key ciphers.
Messages encrypted with the public key can only be decrypted with Messages encrypted with the public key can only be decrypted with
the associated private key. Conversely, messages signed with the the associated private key. Conversely, messages signed with the
private key can be verified with the public key. private key can be verified with the public key.
one-way hash function one-way hash function
A one-way transformation that converts an arbitrary amount of data A one-way transformation that converts an arbitrary amount of data
into a fixed-length hash. It is computationally hard to reverse into a fixed-length hash. It is computationally hard to reverse
the transformation or to find collisions. MD5 and SHA are examples the transformation or to find collisions. MD5 and SHA are
of one-way hash functions. examples of one-way hash functions.
RC4 RC4
A stream cipher invented by Ron Rivest. A compatible cipher is A stream cipher invented by Ron Rivest. A compatible cipher is
described in [SCH]. described in [SCH].
RSA RSA
A very widely used public-key algorithm that can be used for A very widely used public key algorithm that can be used for
either encryption or digital signing. [RSA] either encryption or digital signing. [RSA]
server server
The server is the application entity that responds to requests for The server is the application entity that responds to requests for
connections from clients. See also under client. connections from clients. See also "client".
session session
A TLS session is an association between a client and a server. A TLS session is an association between a client and a server.
Sessions are created by the handshake protocol. Sessions define a Sessions are created by the handshake protocol. Sessions define a
set of cryptographic security parameters that can be shared among set of cryptographic security parameters that can be shared among
multiple connections. Sessions are used to avoid the expensive multiple connections. Sessions are used to avoid the expensive
negotiation of new security parameters for each connection. negotiation of new security parameters for each connection.
session identifier session identifier
A session identifier is a value generated by a server that A session identifier is a value generated by a server that
identifies a particular session. identifies a particular session.
server write key server write key
The key used to encrypt data written by the server. The key used to encrypt data written by the server.
server write MAC key server write MAC key
The secret data used to authenticate data written by the server. The secret data used to authenticate data written by the server.
SHA SHA
The Secure Hash Algorithm [SHS] is defined in FIPS PUB 180-2. It The Secure Hash Algorithm [SHS] is defined in FIPS PUB 180-2. It
produces a 20-byte output. Note that all references to SHA produces a 20-byte output. Note that all references to SHA
(without a numerical suffix) actually use the modified SHA-1 (without a numerical suffix) actually use the modified SHA-1
algorithm. algorithm.
SHA-256 SHA-256
The 256-bit Secure Hash Algorithm is defined in FIPS PUB 180-2. It The 256-bit Secure Hash Algorithm is defined in FIPS PUB 180-2.
produces a 32-byte output. It produces a 32-byte output.
SSL SSL
Netscape's Secure Socket Layer protocol [SSL3]. TLS is based on Netscape's Secure Socket Layer protocol [SSL3]. TLS is based on
SSL Version 3.0 SSL Version 3.0.
stream cipher stream cipher
An encryption algorithm that converts a key into a An encryption algorithm that converts a key into a
cryptographically strong keystream, which is then exclusive-ORed cryptographically strong keystream, which is then exclusive-ORed
with the plaintext. with the plaintext.
symmetric cipher symmetric cipher
See bulk cipher. See bulk cipher.
Transport Layer Security (TLS) Transport Layer Security (TLS)
This protocol; also, the Transport Layer Security working group of This protocol; also, the Transport Layer Security working group of
the Internet Engineering Task Force (IETF). See "Comments" at the the Internet Engineering Task Force (IETF). See "Working Group
end of this document. Information" at the end of this document (see page 99).
Appendix C. Cipher Suite Definitions Appendix C. Cipher Suite Definitions
Cipher Suite Key Cipher Mac Cipher Suite Key Cipher Mac
Exchange Exchange
TLS_NULL_WITH_NULL_NULL NULL NULL NULL TLS_NULL_WITH_NULL_NULL NULL NULL NULL
TLS_RSA_WITH_NULL_MD5 RSA NULL MD5 TLS_RSA_WITH_NULL_MD5 RSA NULL MD5
TLS_RSA_WITH_NULL_SHA RSA NULL SHA TLS_RSA_WITH_NULL_SHA RSA NULL SHA
TLS_RSA_WITH_NULL_SHA256 RSA NULL SHA256 TLS_RSA_WITH_NULL_SHA256 RSA NULL SHA256
TLS_RSA_WITH_RC4_128_MD5 RSA RC4_128 MD5 TLS_RSA_WITH_RC4_128_MD5 RSA RC4_128 MD5
TLS_RSA_WITH_RC4_128_SHA RSA RC4_128 SHA TLS_RSA_WITH_RC4_128_SHA RSA RC4_128 SHA
skipping to change at page 80, line 24 skipping to change at page 84, line 28
SHA256 HMAC-SHA256 32 32 SHA256 HMAC-SHA256 32 32
Type Type
Indicates whether this is a stream cipher or a block cipher Indicates whether this is a stream cipher or a block cipher
running in CBC mode. running in CBC mode.
Key Material Key Material
The number of bytes from the key_block that are used for The number of bytes from the key_block that are used for
generating the write keys. generating the write keys.
Expanded Key Material
The number of bytes actually fed into the encryption algorithm.
IV Size IV Size
The amount of data needed to be generated for the initialization The amount of data needed to be generated for the initialization
vector. Zero for stream ciphers; equal to the block size for block vector. Zero for stream ciphers; equal to the block size for
ciphers (this is equal to SecurityParameters.record_iv_length). block ciphers (this is equal to
SecurityParameters.record_iv_length).
Block Size Block Size
The amount of data a block cipher enciphers in one chunk; a block The amount of data a block cipher enciphers in one chunk; a block
cipher running in CBC mode can only encrypt an even multiple of cipher running in CBC mode can only encrypt an even multiple of
its block size. its block size.
Appendix D. Implementation Notes Appendix D. Implementation Notes
The TLS protocol cannot prevent many common security mistakes. This The TLS protocol cannot prevent many common security mistakes. This
section provides several recommendations to assist implementors. section provides several recommendations to assist implementors.
D.1 Random Number Generation and Seeding D.1. Random Number Generation and Seeding
TLS requires a cryptographically secure pseudorandom number generator TLS requires a cryptographically secure pseudorandom number generator
(PRNG). Care must be taken in designing and seeding PRNGs. PRNGs (PRNG). Care must be taken in designing and seeding PRNGs. PRNGs
based on secure hash operations, most notably SHA-1, are acceptable, based on secure hash operations, most notably SHA-1, are acceptable,
but cannot provide more security than the size of the random number but cannot provide more security than the size of the random number
generator state. generator state.
To estimate the amount of seed material being produced, add the To estimate the amount of seed material being produced, add the
number of bits of unpredictable information in each seed byte. For number of bits of unpredictable information in each seed byte. For
example, keystroke timing values taken from a PC compatible's 18.2 Hz example, keystroke timing values taken from a PC compatible's 18.2 Hz
timer provide 1 or 2 secure bits each, even though the total size of timer provide 1 or 2 secure bits each, even though the total size of
the counter value is 16 bits or more. Seeding a 128-bit PRNG would the counter value is 16 bits or more. Seeding a 128-bit PRNG would
thus require approximately 100 such timer values. thus require approximately 100 such timer values.
[RANDOM] provides guidance on the generation of random values. [RANDOM] provides guidance on the generation of random values.
D.2 Certificates and Authentication D.2. Certificates and Authentication
Implementations are responsible for verifying the integrity of Implementations are responsible for verifying the integrity of
certificates and should generally support certificate revocation certificates and should generally support certificate revocation
messages. Certificates should always be verified to ensure proper messages. Certificates should always be verified to ensure proper
signing by a trusted Certificate Authority (CA). The selection and signing by a trusted Certificate Authority (CA). The selection and
addition of trusted CAs should be done very carefully. Users should addition of trusted CAs should be done very carefully. Users should
be able to view information about the certificate and root CA. be able to view information about the certificate and root CA.
D.3 Cipher Suites D.3. Cipher Suites
TLS supports a range of key sizes and security levels, including some TLS supports a range of key sizes and security levels, including some
that provide no or minimal security. A proper implementation will that provide no or minimal security. A proper implementation will
probably not support many cipher suites. For instance, anonymous probably not support many cipher suites. For instance, anonymous
Diffie-Hellman is strongly discouraged because it cannot prevent man- Diffie-Hellman is strongly discouraged because it cannot prevent man-
in-the-middle attacks. Applications should also enforce minimum and in-the-middle attacks. Applications should also enforce minimum and
maximum key sizes. For example, certificate chains containing 512-bit maximum key sizes. For example, certificate chains containing 512-
RSA keys or signatures are not appropriate for high-security bit RSA keys or signatures are not appropriate for high-security
applications. applications.
D.4 Implementation Pitfalls D.4. Implementation Pitfalls
Implementation experience has shown that certain parts of earlier TLS Implementation experience has shown that certain parts of earlier TLS
specifications are not easy to understand, and have been a source of specifications are not easy to understand, and have been a source of
interoperability and security problems. Many of these areas have been interoperability and security problems. Many of these areas have
clarified in this document, but this appendix contains a short list been clarified in this document, but this appendix contains a short
of the most important things that require special attention from list of the most important things that require special attention from
implementors. implementors.
TLS protocol issues: TLS protocol issues:
- Do you correctly handle handshake messages that are fragmented - Do you correctly handle handshake messages that are fragmented to
to multiple TLS records (see Section 6.2.1)? Including corner multiple TLS records (see Section 6.2.1)? Including corner cases
cases like a ClientHello that is split to several small like a ClientHello that is split to several small fragments? Do
fragments? Do you fragment handshake messages that exceed the you fragment handshake messages that exceed the maximum fragment
maximum fragment size? In particular, the certificate and size? In particular, the certificate and certificate request
certificate request handshake messages can be large enough to handshake messages can be large enough to require fragmentation.
require fragmentation.
- Do you ignore the TLS record layer version number in all TLS - Do you ignore the TLS record layer version number in all TLS
records before ServerHello (see Appendix E.1)? records before ServerHello (see Appendix E.1)?
- Do you handle TLS extensions in ClientHello correctly, - Do you handle TLS extensions in ClientHello correctly, including
including omitting the extensions field completely? omitting the extensions field completely?
- Do you support renegotiation, both client and server initiated? - Do you support renegotiation, both client and server initiated?
While renegotiation is an optional feature, supporting While renegotiation is an optional feature, supporting it is
it is highly recommended. highly recommended.
- When the server has requested a client certificate, but no - When the server has requested a client certificate, but no
suitable certificate is available, do you correctly send suitable certificate is available, do you correctly send an empty
an empty Certificate message, instead of omitting the whole Certificate message, instead of omitting the whole message (see
message (see Section 7.4.6)? Section 7.4.6)?
Cryptographic details: Cryptographic details:
- In RSA-encrypted Premaster Secret, do you correctly send and - In the RSA-encrypted Premaster Secret, do you correctly send and
verify the version number? When an error is encountered, do verify the version number? When an error is encountered, do you
you continue the handshake to avoid the Bleichenbacher continue the handshake to avoid the Bleichenbacher attack (see
attack (see Section 7.4.7.1)? Section 7.4.7.1)?
- What countermeasures do you use to prevent timing attacks against - What countermeasures do you use to prevent timing attacks against
RSA decryption and signing operations (see Section 7.4.7.1)? RSA decryption and signing operations (see Section 7.4.7.1)?
- When verifying RSA signatures, do you accept both NULL and - When verifying RSA signatures, do you accept both NULL and missing
missing parameters (see Section 4.7)? Do you verify that the parameters (see Section 4.7)? Do you verify that the RSA padding
RSA padding doesn't have additional data after the hash value? doesn't have additional data after the hash value? [FI06]
[FI06]
- When using Diffie-Hellman key exchange, do you correctly strip - When using Diffie-Hellman key exchange, do you correctly strip
leading zero bytes from the negotiated key (see Section 8.1.2)? leading zero bytes from the negotiated key (see Section 8.1.2)?
- Does your TLS client check that the Diffie-Hellman parameters - Does your TLS client check that the Diffie-Hellman parameters sent
sent by the server are acceptable (see Section F.1.1.3)? by the server are acceptable (see Section F.1.1.3)?
- How do you generate unpredictable IVs for CBC mode ciphers
(see Section 6.2.3.2)?
- Do you accept long CBC mode padding (up to 255 bytes; see - How do you generate unpredictable IVs for CBC mode ciphers (see
Section 6.2.3.2)? Section 6.2.3.2)?
- Do you accept long CBC mode padding (up to 255 bytes; see Section
6.2.3.2)?
- How do you address CBC mode timing attacks (Section 6.2.3.2)? - How do you address CBC mode timing attacks (Section 6.2.3.2)?
- Do you use a strong and, most importantly, properly seeded - Do you use a strong and, most importantly, properly seeded random
random number generator (see Appendix D.1) for generating the number generator (see Appendix D.1) for generating the premaster
premaster secret (for RSA key exchange), Diffie-Hellman private secret (for RSA key exchange), Diffie-Hellman private values, the
values, the DSA "k" parameter, and other security-critical DSA "k" parameter, and other security-critical values?
values?
Appendix E. Backward Compatibility Appendix E. Backward Compatibility
E.1 Compatibility with TLS 1.0/1.1 and SSL 3.0 E.1. Compatibility with TLS 1.0/1.1 and SSL 3.0
Since there are various versions of TLS (1.0, 1.1, 1.2, and any Since there are various versions of TLS (1.0, 1.1, 1.2, and any
future versions) and SSL (2.0 and 3.0), means are needed to negotiate future versions) and SSL (2.0 and 3.0), means are needed to negotiate
the specific protocol version to use. The TLS protocol provides a the specific protocol version to use. The TLS protocol provides a
built-in mechanism for version negotiation so as not to bother other built-in mechanism for version negotiation so as not to bother other
protocol components with the complexities of version selection. protocol components with the complexities of version selection.
TLS versions 1.0, 1.1, and 1.2, and SSL 3.0 are very similar, and use TLS versions 1.0, 1.1, and 1.2, and SSL 3.0 are very similar, and use
compatible ClientHello messages; thus, supporting all of them is compatible ClientHello messages; thus, supporting all of them is
relatively easy. Similarly, servers can easily handle clients trying relatively easy. Similarly, servers can easily handle clients trying
to use future versions of TLS as long as the ClientHello format to use future versions of TLS as long as the ClientHello format
remains compatible, and the client supports the highest protocol remains compatible, and the client supports the highest protocol
version available in the server. version available in the server.
A TLS 1.2 client who wishes to negotiate with such older servers will A TLS 1.2 client who wishes to negotiate with such older servers will
send a normal TLS 1.2 ClientHello, containing { 3, 3 } (TLS 1.2) in send a normal TLS 1.2 ClientHello, containing { 3, 3 } (TLS 1.2) in
ClientHello.client_version. If the server does not support this ClientHello.client_version. If the server does not support this
version, it will respond with ServerHello containing an older version version, it will respond with a ServerHello containing an older
number. If the client agrees to use this version, the negotiation version number. If the client agrees to use this version, the
will proceed as appropriate for the negotiated protocol. negotiation will proceed as appropriate for the negotiated protocol.
If the version chosen by the server is not supported by the client If the version chosen by the server is not supported by the client
(or not acceptable), the client MUST send a "protocol_version" alert (or not acceptable), the client MUST send a "protocol_version" alert
message and close the connection. message and close the connection.
If a TLS server receives a ClientHello containing a version number If a TLS server receives a ClientHello containing a version number
greater than the highest version supported by the server, it MUST greater than the highest version supported by the server, it MUST
reply according to the highest version supported by the server. reply according to the highest version supported by the server.
A TLS server can also receive a ClientHello containing a version A TLS server can also receive a ClientHello containing a version
number smaller than the highest supported version. If the server number smaller than the highest supported version. If the server
wishes to negotiate with old clients, it will proceed as appropriate wishes to negotiate with old clients, it will proceed as appropriate
for the highest version supported by the server that is not greater for the highest version supported by the server that is not greater
than ClientHello.client_version. For example, if the server supports than ClientHello.client_version. For example, if the server supports
TLS 1.0, 1.1, and 1.2, and client_version is TLS 1.0, the server will TLS 1.0, 1.1, and 1.2, and client_version is TLS 1.0, the server will
proceed with a TLS 1.0 ServerHello. If server supports (or is willing proceed with a TLS 1.0 ServerHello. If server supports (or is
to use) only versions greater than client_version, it MUST send a willing to use) only versions greater than client_version, it MUST
"protocol_version" alert message and close the connection. send a "protocol_version" alert message and close the connection.
Whenever a client already knows the highest protocol version known to Whenever a client already knows the highest protocol version known to
a server (for example, when resuming a session), it SHOULD initiate a server (for example, when resuming a session), it SHOULD initiate
the connection in that native protocol. the connection in that native protocol.
Note: some server implementations are known to implement version Note: some server implementations are known to implement version
negotiation incorrectly. For example, there are buggy TLS 1.0 servers negotiation incorrectly. For example, there are buggy TLS 1.0
that simply close the connection when the client offers a version servers that simply close the connection when the client offers a
newer than TLS 1.0. Also, it is known that some servers will refuse version newer than TLS 1.0. Also, it is known that some servers will
the connection if any TLS extensions are included in ClientHello. refuse the connection if any TLS extensions are included in
Interoperability with such buggy servers is a complex topic beyond ClientHello. Interoperability with such buggy servers is a complex
the scope of this document, and may require multiple connection topic beyond the scope of this document, and may require multiple
attempts by the client. connection attempts by the client.
Earlier versions of the TLS specification were not fully clear on Earlier versions of the TLS specification were not fully clear on
what the record layer version number (TLSPlaintext.version) should what the record layer version number (TLSPlaintext.version) should
contain when sending ClientHello (i.e., before it is known which contain when sending ClientHello (i.e., before it is known which
version of the protocol will be employed). Thus, TLS servers version of the protocol will be employed). Thus, TLS servers
compliant with this specification MUST accept any value {03,XX} as compliant with this specification MUST accept any value {03,XX} as
the record layer version number for ClientHello. the record layer version number for ClientHello.
TLS clients that wish to negotiate with older servers MAY send any TLS clients that wish to negotiate with older servers MAY send any
value {03,XX} as the record layer version number. Typical values value {03,XX} as the record layer version number. Typical values
would be {03,00}, the lowest version number supported by the client, would be {03,00}, the lowest version number supported by the client,
and the value of ClientHello.client_version. No single value will and the value of ClientHello.client_version. No single value will
guarantee interoperability with all old servers, but this is a guarantee interoperability with all old servers, but this is a
complex topic beyond the scope of this document. complex topic beyond the scope of this document.
E.2 Compatibility with SSL 2.0 E.2. Compatibility with SSL 2.0
TLS 1.2 clients that wish to support SSL 2.0 servers MUST send TLS 1.2 clients that wish to support SSL 2.0 servers MUST send
version 2.0 CLIENT-HELLO messages defined in [SSL2]. The message MUST version 2.0 CLIENT-HELLO messages defined in [SSL2]. The message
contain the same version number as would be used for ordinary MUST contain the same version number as would be used for ordinary
ClientHello, and MUST encode the supported TLS cipher suites in the ClientHello, and MUST encode the supported TLS cipher suites in the
CIPHER-SPECS-DATA field as described below. CIPHER-SPECS-DATA field as described below.
Warning: The ability to send version 2.0 CLIENT-HELLO messages will Warning: The ability to send version 2.0 CLIENT-HELLO messages will
be phased out with all due haste, since the newer ClientHello format be phased out with all due haste, since the newer ClientHello format
provides better mechanisms for moving to newer versions and provides better mechanisms for moving to newer versions and
negotiating extensions. TLS 1.2 clients SHOULD NOT support SSL 2.0. negotiating extensions. TLS 1.2 clients SHOULD NOT support SSL 2.0.
However, even TLS servers that do not support SSL 2.0 MAY accept However, even TLS servers that do not support SSL 2.0 MAY accept
version 2.0 CLIENT-HELLO messages. The message is presented below in version 2.0 CLIENT-HELLO messages. The message is presented below in
sufficient detail for TLS server implementors; the true definition is sufficient detail for TLS server implementors; the true definition is
still assumed to be [SSL2]. still assumed to be [SSL2].
For negotiation purposes, 2.0 CLIENT-HELLO is interpreted the same For negotiation purposes, 2.0 CLIENT-HELLO is interpreted the same
way as a ClientHello with a "null" compression method and no way as a ClientHello with a "null" compression method and no
extensions. Note that this message MUST be sent directly on the wire, extensions. Note that this message MUST be sent directly on the
not wrapped as a TLS record. For the purposes of calculating Finished wire, not wrapped as a TLS record. For the purposes of calculating
and CertificateVerify, the msg_length field is not considered to be a Finished and CertificateVerify, the msg_length field is not
part of the handshake message. considered to be a part of the handshake message.
uint8 V2CipherSpec[3]; uint8 V2CipherSpec[3];
struct { struct {
uint16 msg_length; uint16 msg_length;
uint8 msg_type; uint8 msg_type;
Version version; Version version;
uint16 cipher_spec_length; uint16 cipher_spec_length;
uint16 session_id_length; uint16 session_id_length;
uint16 challenge_length; uint16 challenge_length;
V2CipherSpec cipher_specs[V2ClientHello.cipher_spec_length]; V2CipherSpec cipher_specs[V2ClientHello.cipher_spec_length];
opaque session_id[V2ClientHello.session_id_length]; opaque session_id[V2ClientHello.session_id_length];
opaque challenge[V2ClientHello.challenge_length; opaque challenge[V2ClientHello.challenge_length;
} V2ClientHello; } V2ClientHello;
msg_length msg_length
The highest bit MUST be 1; the remaining bits contain the length The highest bit MUST be 1; the remaining bits contain the length
of the following data in bytes. of the following data in bytes.
msg_type msg_type
This field, in conjunction with the version field, identifies a This field, in conjunction with the version field, identifies a
version 2 client hello message. The value MUST be one (1). version 2 ClientHello message. The value MUST be 1.
version version
Equal to ClientHello.client_version. Equal to ClientHello.client_version.
cipher_spec_length cipher_spec_length
This field is the total length of the field cipher_specs. It This field is the total length of the field cipher_specs. It
cannot be zero and MUST be a multiple of the V2CipherSpec length cannot be zero and MUST be a multiple of the V2CipherSpec length
(3). (3).
session_id_length session_id_length
This field MUST have a value of zero for a client that claims to This field MUST have a value of zero for a client that claims to
support TLS 1.2. support TLS 1.2.
challenge_length challenge_length
The length in bytes of the client's challenge to the server to The length in bytes of the client's challenge to the server to
authenticate itself. Historically, permissible values are between authenticate itself. Historically, permissible values are between
16 and 32 bytes inclusive. When using the SSLv2 backward 16 and 32 bytes inclusive. When using the SSLv2 backward-
compatible handshake the client SHOULD use a 32 byte challenge. compatible handshake the client SHOULD use a 32-byte challenge.
cipher_specs cipher_specs
This is a list of all CipherSpecs the client is willing and able This is a list of all CipherSpecs the client is willing and able
to use. In addition to the 2.0 cipher specs defined in [SSL2], to use. In addition to the 2.0 cipher specs defined in [SSL2],
this includes the TLS cipher suites normally sent in this includes the TLS cipher suites normally sent in
ClientHello.cipher_suites, each cipher suite prefixed by a zero ClientHello.cipher_suites, with each cipher suite prefixed by a
byte. For example, TLS cipher suite {0x00,0x0A} would be sent as zero byte. For example, the TLS cipher suite {0x00,0x0A} would be
{0x00,0x00,0x0A}. sent as {0x00,0x00,0x0A}.
session_id session_id
This field MUST be empty. This field MUST be empty.
challenge challenge
Corresponds to ClientHello.random. If the challenge length is less Corresponds to ClientHello.random. If the challenge length is
than 32, the TLS server will pad the data with leading (note: not less than 32, the TLS server will pad the data with leading (note:
trailing) zero bytes to make it 32 bytes long. not trailing) zero bytes to make it 32 bytes long.
Note: Requests to resume a TLS session MUST use a TLS client hello. Note: Requests to resume a TLS session MUST use a TLS client hello.
E.3. Avoiding Man-in-the-Middle Version Rollback E.3. Avoiding Man-in-the-Middle Version Rollback
When TLS clients fall back to Version 2.0 compatibility mode, they When TLS clients fall back to Version 2.0 compatibility mode, they
MUST use special PKCS#1 block formatting. This is done so that TLS MUST use special PKCS#1 block formatting. This is done so that TLS
servers will reject Version 2.0 sessions with TLS-capable clients. servers will reject Version 2.0 sessions with TLS-capable clients.
When a client negotiates SSL 2.0 but also supports TLS, it MUST set When a client negotiates SSL 2.0 but also supports TLS, it MUST set
the right-hand (least-significant) 8 random bytes of the PKCS padding the right-hand (least-significant) 8 random bytes of the PKCS padding
(not including the terminal null of the padding) for the RSA (not including the terminal null of the padding) for the RSA
encryption of the ENCRYPTED-KEY-DATA field of the CLIENT-MASTER-KEY encryption of the ENCRYPTED-KEY-DATA field of the CLIENT-MASTER-KEY
to 0x03 (the other padding bytes are random). to 0x03 (the other padding bytes are random).
When a TLS-capable server negotiates SSL 2.0 it SHOULD, after When a TLS-capable server negotiates SSL 2.0 it SHOULD, after
decrypting the ENCRYPTED-KEY-DATA field, check that these eight decrypting the ENCRYPTED-KEY-DATA field, check that these 8 padding
padding bytes are 0x03. If they are not, the server SHOULD generate a bytes are 0x03. If they are not, the server SHOULD generate a random
random value for SECRET-KEY-DATA, and continue the handshake (which value for SECRET-KEY-DATA, and continue the handshake (which will
will eventually fail since the keys will not match). Note that eventually fail since the keys will not match). Note that reporting
reporting the error situation to the client could make the server the error situation to the client could make the server vulnerable to
vulnerable to attacks described in [BLEI]. attacks described in [BLEI].
Appendix F. Security Analysis Appendix F. Security Analysis
The TLS protocol is designed to establish a secure connection between The TLS protocol is designed to establish a secure connection between
a client and a server communicating over an insecure channel. This a client and a server communicating over an insecure channel. This
document makes several traditional assumptions, including that document makes several traditional assumptions, including that
attackers have substantial computational resources and cannot obtain attackers have substantial computational resources and cannot obtain
secret information from sources outside the protocol. Attackers are secret information from sources outside the protocol. Attackers are
assumed to have the ability to capture, modify, delete, replay, and assumed to have the ability to capture, modify, delete, replay, and
otherwise tamper with messages sent over the communication channel. otherwise tamper with messages sent over the communication channel.
This appendix outlines how TLS has been designed to resist a variety This appendix outlines how TLS has been designed to resist a variety
of attacks. of attacks.
F.1. Handshake Protocol F.1. Handshake Protocol
The handshake protocol is responsible for selecting a CipherSpec and The handshake protocol is responsible for selecting a cipher spec and
generating a Master Secret, which together comprise the primary generating a master secret, which together comprise the primary
cryptographic parameters associated with a secure session. The cryptographic parameters associated with a secure session. The
handshake protocol can also optionally authenticate parties who have handshake protocol can also optionally authenticate parties who have
certificates signed by a trusted certificate authority. certificates signed by a trusted certificate authority.
F.1.1. Authentication and Key Exchange F.1.1. Authentication and Key Exchange
TLS supports three authentication modes: authentication of both TLS supports three authentication modes: authentication of both
parties, server authentication with an unauthenticated client, and parties, server authentication with an unauthenticated client, and
total anonymity. Whenever the server is authenticated, the channel is total anonymity. Whenever the server is authenticated, the channel
secure against man-in-the-middle attacks, but completely anonymous is secure against man-in-the-middle attacks, but completely anonymous
sessions are inherently vulnerable to such attacks. Anonymous sessions are inherently vulnerable to such attacks. Anonymous
servers cannot authenticate clients. If the server is authenticated, servers cannot authenticate clients. If the server is authenticated,
its certificate message must provide a valid certificate chain its certificate message must provide a valid certificate chain
leading to an acceptable certificate authority. Similarly, leading to an acceptable certificate authority. Similarly,
authenticated clients must supply an acceptable certificate to the authenticated clients must supply an acceptable certificate to the
server. Each party is responsible for verifying that the other's server. Each party is responsible for verifying that the other's
certificate is valid and has not expired or been revoked. certificate is valid and has not expired or been revoked.
The general goal of the key exchange process is to create a The general goal of the key exchange process is to create a
pre_master_secret known to the communicating parties and not to pre_master_secret known to the communicating parties and not to
attackers. The pre_master_secret will be used to generate the attackers. The pre_master_secret will be used to generate the
master_secret (see Section 8.1). The master_secret is required to master_secret (see Section 8.1). The master_secret is required to
generate the finished messages, encryption keys, and MAC keys (see generate the Finished messages, encryption keys, and MAC keys (see
Sections 7.4.9 and 6.3). By sending a correct finished message, Sections 7.4.9 and 6.3). By sending a correct Finished message,
parties thus prove that they know the correct pre_master_secret. parties thus prove that they know the correct pre_master_secret.
F.1.1.1. Anonymous Key Exchange F.1.1.1. Anonymous Key Exchange
Completely anonymous sessions can be established using Diffie-Hellman Completely anonymous sessions can be established using Diffie-Hellman
for key exchange. The server's public parameters are contained in the for key exchange. The server's public parameters are contained in
server key exchange message and the client's are sent in the client the server key exchange message, and the client's are sent in the
key exchange message. Eavesdroppers who do not know the private client key exchange message. Eavesdroppers who do not know the
values should not be able to find the Diffie-Hellman result (i.e. the private values should not be able to find the Diffie-Hellman result
pre_master_secret). (i.e., the pre_master_secret).
Warning: Completely anonymous connections only provide protection Warning: Completely anonymous connections only provide protection
against passive eavesdropping. Unless an independent tamper-proof against passive eavesdropping. Unless an independent tamper-proof
channel is used to verify that the finished messages were not channel is used to verify that the Finished messages were not
replaced by an attacker, server authentication is required in replaced by an attacker, server authentication is required in
environments where active man-in-the-middle attacks are a concern. environments where active man-in-the-middle attacks are a concern.
F.1.1.2. RSA Key Exchange and Authentication F.1.1.2. RSA Key Exchange and Authentication
With RSA, key exchange and server authentication are combined. The With RSA, key exchange and server authentication are combined. The
public key is contained in the server's certificate. Note that public key is contained in the server's certificate. Note that
compromise of the server's static RSA key results in a loss of compromise of the server's static RSA key results in a loss of
confidentiality for all sessions protected under that static key. TLS confidentiality for all sessions protected under that static key.
users desiring Perfect Forward Secrecy should use DHE cipher suites. TLS users desiring Perfect Forward Secrecy should use DHE cipher
The damage done by exposure of a private key can be limited by suites. The damage done by exposure of a private key can be limited
changing one's private key (and certificate) frequently. by changing one's private key (and certificate) frequently.
After verifying the server's certificate, the client encrypts a After verifying the server's certificate, the client encrypts a
pre_master_secret with the server's public key. By successfully pre_master_secret with the server's public key. By successfully
decoding the pre_master_secret and producing a correct finished decoding the pre_master_secret and producing a correct Finished
message, the server demonstrates that it knows the private key message, the server demonstrates that it knows the private key
corresponding to the server certificate. corresponding to the server certificate.
When RSA is used for key exchange, clients are authenticated using When RSA is used for key exchange, clients are authenticated using
the certificate verify message (see Section 7.4.8). The client signs the certificate verify message (see Section 7.4.8). The client signs
a value derived from all preceding handshake messages. These a value derived from all preceding handshake messages. These
handshake messages include the server certificate, which binds the handshake messages include the server certificate, which binds the
signature to the server, and ServerHello.random, which binds the signature to the server, and ServerHello.random, which binds the
signature to the current handshake process. signature to the current handshake process.
F.1.1.3. Diffie-Hellman Key Exchange with Authentication F.1.1.3. Diffie-Hellman Key Exchange with Authentication
When Diffie-Hellman key exchange is used, the server can either When Diffie-Hellman key exchange is used, the server can either
supply a certificate containing fixed Diffie-Hellman parameters or supply a certificate containing fixed Diffie-Hellman parameters or
use the server key exchange message to send a set of temporary use the server key exchange message to send a set of temporary
Diffie-Hellman parameters signed with a DSA or RSA certificate. Diffie-Hellman parameters signed with a DSA or RSA certificate.
Temporary parameters are hashed with the hello.random values before Temporary parameters are hashed with the hello.random values before
signing to ensure that attackers do not replay old parameters. In signing to ensure that attackers do not replay old parameters. In
either case, the client can verify the certificate or signature to either case, the client can verify the certificate or signature to
ensure that the parameters belong to the server. ensure that the parameters belong to the server.
If the client has a certificate containing fixed Diffie-Hellman If the client has a certificate containing fixed Diffie-Hellman
parameters, its certificate contains the information required to parameters, its certificate contains the information required to
complete the key exchange. Note that in this case the client and complete the key exchange. Note that in this case the client and
server will generate the same Diffie-Hellman result (i.e., server will generate the same Diffie-Hellman result (i.e.,
pre_master_secret) every time they communicate. To prevent the pre_master_secret) every time they communicate. To prevent the
pre_master_secret from staying in memory any longer than necessary, pre_master_secret from staying in memory any longer than necessary,
it should be converted into the master_secret as soon as possible. it should be converted into the master_secret as soon as possible.
Client Diffie-Hellman parameters must be compatible with those Client Diffie-Hellman parameters must be compatible with those
supplied by the server for the key exchange to work. supplied by the server for the key exchange to work.
If the client has a standard DSA or RSA certificate or is If the client has a standard DSA or RSA certificate or is
unauthenticated, it sends a set of temporary parameters to the server unauthenticated, it sends a set of temporary parameters to the server
in the client key exchange message, then optionally uses a in the client key exchange message, then optionally uses a
certificate verify message to authenticate itself. certificate verify message to authenticate itself.
If the same DH keypair is to be used for multiple handshakes, either If the same DH keypair is to be used for multiple handshakes, either
because the client or server has a certificate containing a fixed DH because the client or server has a certificate containing a fixed DH
keypair or because the server is reusing DH keys, care must be taken keypair or because the server is reusing DH keys, care must be taken
to prevent small subgroup attacks. Implementations SHOULD follow the to prevent small subgroup attacks. Implementations SHOULD follow the
guidelines found in [SUBGROUP]. guidelines found in [SUBGROUP].
Small subgroup attacks are most easily avoided by using one of the Small subgroup attacks are most easily avoided by using one of the
DHE cipher suites and generating a fresh DH private key (X) for each DHE cipher suites and generating a fresh DH private key (X) for each
handshake. If a suitable base (such as 2) is chosen, g^X mod p can be handshake. If a suitable base (such as 2) is chosen, g^X mod p can
computed very quickly, therefore the performance cost is minimized. be computed very quickly; therefore, the performance cost is
Additionally, using a fresh key for each handshake provides Perfect minimized. Additionally, using a fresh key for each handshake
Forward Secrecy. Implementations SHOULD generate a new X for each provides Perfect Forward Secrecy. Implementations SHOULD generate a
handshake when using DHE cipher suites. new X for each handshake when using DHE cipher suites.
Because TLS allows the server to provide arbitrary DH groups, the Because TLS allows the server to provide arbitrary DH groups, the
client should verify that the DH group is of suitable size as defined client should verify that the DH group is of suitable size as defined
by local policy. The client SHOULD also verify that the DH public by local policy. The client SHOULD also verify that the DH public
exponent appears to be of adequate size. [KEYSIZ] provides a useful exponent appears to be of adequate size. [KEYSIZ] provides a useful
guide to the strength of various group sizes. The server MAY choose guide to the strength of various group sizes. The server MAY choose
to assist the client by providing a known group, such as those to assist the client by providing a known group, such as those
defined in [IKEALG] or [MODP]. These can be verified by simple defined in [IKEALG] or [MODP]. These can be verified by simple
comparison. comparison.
F.1.2. Version Rollback Attacks F.1.2. Version Rollback Attacks
Because TLS includes substantial improvements over SSL Version 2.0, Because TLS includes substantial improvements over SSL Version 2.0,
attackers may try to make TLS-capable clients and servers fall back attackers may try to make TLS-capable clients and servers fall back
to Version 2.0. This attack can occur if (and only if) two TLS- to Version 2.0. This attack can occur if (and only if) two TLS-
capable parties use an SSL 2.0 handshake. capable parties use an SSL 2.0 handshake.
Although the solution using non-random PKCS #1 block type 2 message Although the solution using non-random PKCS #1 block type 2 message
padding is inelegant, it provides a reasonably secure way for Version padding is inelegant, it provides a reasonably secure way for Version
3.0 servers to detect the attack. This solution is not secure against 3.0 servers to detect the attack. This solution is not secure
attackers who can brute force the key and substitute a new ENCRYPTED- against attackers who can brute-force the key and substitute a new
KEY-DATA message containing the same key (but with normal padding) ENCRYPTED-KEY-DATA message containing the same key (but with normal
before the application specified wait threshold has expired. Altering padding) before the application-specified wait threshold has expired.
the padding of the least significant 8 bytes of the PKCS padding does Altering the padding of the least-significant 8 bytes of the PKCS
not impact security for the size of the signed hashes and RSA key padding does not impact security for the size of the signed hashes
lengths used in the protocol, since this is essentially equivalent to and RSA key lengths used in the protocol, since this is essentially
increasing the input block size by 8 bytes. equivalent to increasing the input block size by 8 bytes.
F.1.3. Detecting Attacks Against the Handshake Protocol F.1.3. Detecting Attacks Against the Handshake Protocol
An attacker might try to influence the handshake exchange to make the An attacker might try to influence the handshake exchange to make the
parties select different encryption algorithms than they would parties select different encryption algorithms than they would
normally chooses. normally choose.
For this attack, an attacker must actively change one or more For this attack, an attacker must actively change one or more
handshake messages. If this occurs, the client and server will handshake messages. If this occurs, the client and server will
compute different values for the handshake message hashes. As a compute different values for the handshake message hashes. As a
result, the parties will not accept each others' finished messages. result, the parties will not accept each others' Finished messages.
Without the master_secret, the attacker cannot repair the finished Without the master_secret, the attacker cannot repair the Finished
messages, so the attack will be discovered. messages, so the attack will be discovered.
F.1.4. Resuming Sessions F.1.4. Resuming Sessions
When a connection is established by resuming a session, new When a connection is established by resuming a session, new
ClientHello.random and ServerHello.random values are hashed with the ClientHello.random and ServerHello.random values are hashed with the
session's master_secret. Provided that the master_secret has not been session's master_secret. Provided that the master_secret has not
compromised and that the secure hash operations used to produce the been compromised and that the secure hash operations used to produce
encryption keys and MAC keys are secure, the connection should be the encryption keys and MAC keys are secure, the connection should be
secure and effectively independent from previous connections. secure and effectively independent from previous connections.
Attackers cannot use known encryption keys or MAC secrets to Attackers cannot use known encryption keys or MAC secrets to
compromise the master_secret without breaking the secure hash compromise the master_secret without breaking the secure hash
operations. operations.
Sessions cannot be resumed unless both the client and server agree. Sessions cannot be resumed unless both the client and server agree.
If either party suspects that the session may have been compromised, If either party suspects that the session may have been compromised,
or that certificates may have expired or been revoked, it should or that certificates may have expired or been revoked, it should
force a full handshake. An upper limit of 24 hours is suggested for force a full handshake. An upper limit of 24 hours is suggested for
session ID lifetimes, since an attacker who obtains a master_secret session ID lifetimes, since an attacker who obtains a master_secret
may be able to impersonate the compromised party until the may be able to impersonate the compromised party until the
corresponding session ID is retired. Applications that may be run in corresponding session ID is retired. Applications that may be run in
relatively insecure environments should not write session IDs to relatively insecure environments should not write session IDs to
stable storage. stable storage.
F.2. Protecting Application Data F.2. Protecting Application Data
The master_secret is hashed with the ClientHello.random and The master_secret is hashed with the ClientHello.random and
ServerHello.random to produce unique data encryption keys and MAC ServerHello.random to produce unique data encryption keys and MAC
secrets for each connection. secrets for each connection.
Outgoing data is protected with a MAC before transmission. To prevent Outgoing data is protected with a MAC before transmission. To
message replay or modification attacks, the MAC is computed from the prevent message replay or modification attacks, the MAC is computed
MAC key, the sequence number, the message length, the message from the MAC key, the sequence number, the message length, the
contents, and two fixed character strings. The message type field is message contents, and two fixed character strings. The message type
necessary to ensure that messages intended for one TLS Record Layer field is necessary to ensure that messages intended for one TLS
client are not redirected to another. The sequence number ensures record layer client are not redirected to another. The sequence
that attempts to delete or reorder messages will be detected. Since number ensures that attempts to delete or reorder messages will be
sequence numbers are 64 bits long, they should never overflow. detected. Since sequence numbers are 64 bits long, they should never
Messages from one party cannot be inserted into the other's output, overflow. Messages from one party cannot be inserted into the
since they use independent MAC keys. Similarly, the server-write and other's output, since they use independent MAC keys. Similarly, the
client-write keys are independent, so stream cipher keys are used server write and client write keys are independent, so stream cipher
only once. keys are used only once.
If an attacker does break an encryption key, all messages encrypted If an attacker does break an encryption key, all messages encrypted
with it can be read. Similarly, compromise of a MAC key can make with it can be read. Similarly, compromise of a MAC key can make
message modification attacks possible. Because MACs are also message-modification attacks possible. Because MACs are also
encrypted, message-alteration attacks generally require breaking the encrypted, message-alteration attacks generally require breaking the
encryption algorithm as well as the MAC. encryption algorithm as well as the MAC.
Note: MAC keys may be larger than encryption keys, so messages can Note: MAC keys may be larger than encryption keys, so messages can
remain tamper resistant even if encryption keys are broken. remain tamper resistant even if encryption keys are broken.
F.3. Explicit IVs F.3. Explicit IVs
[CBCATT] describes a chosen plaintext attack on TLS that depends on [CBCATT] describes a chosen plaintext attack on TLS that depends on
knowing the IV for a record. Previous versions of TLS [TLS1.0] used knowing the IV for a record. Previous versions of TLS [TLS1.0] used
the CBC residue of the previous record as the IV and therefore the CBC residue of the previous record as the IV and therefore
enabled this attack. This version uses an explicit IV in order to enabled this attack. This version uses an explicit IV in order to
protect against this attack. protect against this attack.
F.4. Security of Composite Cipher Modes F.4. Security of Composite Cipher Modes
TLS secures transmitted application data via the use of symmetric TLS secures transmitted application data via the use of symmetric
encryption and authentication functions defined in the negotiated encryption and authentication functions defined in the negotiated
cipher suite. The objective is to protect both the integrity and cipher suite. The objective is to protect both the integrity and
confidentiality of the transmitted data from malicious actions by confidentiality of the transmitted data from malicious actions by
active attackers in the network. It turns out that the order in active attackers in the network. It turns out that the order in
which encryption and authentication functions are applied to the data which encryption and authentication functions are applied to the data
plays an important role for achieving this goal [ENCAUTH]. plays an important role for achieving this goal [ENCAUTH].
The most robust method, called encrypt-then-authenticate, first The most robust method, called encrypt-then-authenticate, first
skipping to change at page 93, line 15 skipping to change at page 96, line 17
that combined with any secure MAC function, fail to provide the that combined with any secure MAC function, fail to provide the
confidentiality goal against an active attack. Therefore, new cipher confidentiality goal against an active attack. Therefore, new cipher
suites and operation modes adopted into TLS need to be analyzed under suites and operation modes adopted into TLS need to be analyzed under
the authenticate-then-encrypt method to verify that they achieve the the authenticate-then-encrypt method to verify that they achieve the
stated integrity and confidentiality goals. stated integrity and confidentiality goals.
Currently, the security of the authenticate-then-encrypt method has Currently, the security of the authenticate-then-encrypt method has
been proven for some important cases. One is the case of stream been proven for some important cases. One is the case of stream
ciphers in which a computationally unpredictable pad of the length of ciphers in which a computationally unpredictable pad of the length of
the message, plus the length of the MAC tag, is produced using a the message, plus the length of the MAC tag, is produced using a
pseudo-random generator and this pad is xor-ed with the concatenation pseudorandom generator and this pad is exclusive-ORed with the
of plaintext and MAC tag. The other is the case of CBC mode using a concatenation of plaintext and MAC tag. The other is the case of CBC
secure block cipher. In this case, security can be shown if one mode using a secure block cipher. In this case, security can be
applies one CBC encryption pass to the concatenation of plaintext and shown if one applies one CBC encryption pass to the concatenation of
MAC and uses a new, independent, and unpredictable IV for each new plaintext and MAC and uses a new, independent, and unpredictable IV
pair of plaintext and MAC. In versions of TLS prior to 1.1, CBC mode for each new pair of plaintext and MAC. In versions of TLS prior to
was used properly EXCEPT that it used a predictable IV in the form of 1.1, CBC mode was used properly EXCEPT that it used a predictable IV
the last block of the previous ciphertext. This made TLS open to in the form of the last block of the previous ciphertext. This made
chosen plaintext attacks. This version of the protocol is immune to TLS open to chosen plaintext attacks. This version of the protocol
those attacks. For exact details in the encryption modes proven is immune to those attacks. For exact details in the encryption
secure, see [ENCAUTH]. modes proven secure, see [ENCAUTH].
F.5 Denial of Service F.5. Denial of Service
TLS is susceptible to a number of denial of service (DoS) attacks. TLS is susceptible to a number of denial-of-service (DoS) attacks.
In particular, an attacker who initiates a large number of TCP In particular, an attacker who initiates a large number of TCP
connections can cause a server to consume large amounts of CPU doing connections can cause a server to consume large amounts of CPU for
RSA decryption. However, because TLS is generally used over TCP, it doing RSA decryption. However, because TLS is generally used over
is difficult for the attacker to hide his point of origin if proper TCP, it is difficult for the attacker to hide his point of origin if
TCP SYN randomization is used [SEQNUM] by the TCP stack. proper TCP SYN randomization is used [SEQNUM] by the TCP stack.
Because TLS runs over TCP, it is also susceptible to a number of Because TLS runs over TCP, it is also susceptible to a number of DoS
denial of service attacks on individual connections. In particular, attacks on individual connections. In particular, attackers can
attackers can forge RSTs, thereby terminating connections, or forge forge RSTs, thereby terminating connections, or forge partial TLS
partial TLS records, thereby causing the connection to stall. These records, thereby causing the connection to stall. These attacks
attacks cannot in general be defended against by a TCP-using cannot in general be defended against by a TCP-using protocol.
protocol. Implementors or users who are concerned with this class of Implementors or users who are concerned with this class of attack
attack should use IPsec AH [AH] or ESP [ESP]. should use IPsec AH [AH] or ESP [ESP].
F.6 Final Notes F.6. Final Notes
For TLS to be able to provide a secure connection, both the client For TLS to be able to provide a secure connection, both the client
and server systems, keys, and applications must be secure. In and server systems, keys, and applications must be secure. In
addition, the implementation must be free of security errors. addition, the implementation must be free of security errors.
The system is only as strong as the weakest key exchange and The system is only as strong as the weakest key exchange and
authentication algorithm supported, and only trustworthy authentication algorithm supported, and only trustworthy
cryptographic functions should be used. Short public keys and cryptographic functions should be used. Short public keys and
anonymous servers should be used with great caution. Implementations anonymous servers should be used with great caution. Implementations
and users must be careful when deciding which certificates and and users must be careful when deciding which certificates and
certificate authorities are acceptable; a dishonest certificate certificate authorities are acceptable; a dishonest certificate
authority can do tremendous damage. authority can do tremendous damage.
Changes in This Version
[RFC Editor: Please delete this]
Clarified traffic analysis considerations
Added support for SHA-224 for signatures (though not for HMAC).
Consistent use of camelback style for references to messages (e.g.,
ServerHelloDone) in the text.
Changed "DSS" to "DSA" where we are referring to the algorithm.
Extensive editorial revisions from Alfred Hoenes.
Normative References Normative References
[AES] National Institute of Standards and Technology, [AES] National Institute of Standards and Technology,
"Specification for the Advanced Encryption Standard (AES)" "Specification for the Advanced Encryption Standard (AES)"
FIPS 197. November 26, 2001. FIPS 197. November 26, 2001.
[3DES] National Institute of Standards and Technology, [3DES] National Institute of Standards and Technology,
"Recommendation for the Triple Data Encryption Algorithm "Recommendation for the Triple Data Encryption Algorithm
(TDEA) Block Cipher", NIST Special Publication 800-67, May (TDEA) Block Cipher", NIST Special Publication 800-67, May
2004. 2004.
[DSS] NIST FIPS PUB 186-2, "Digital Signature Standard", National [DSS] NIST FIPS PUB 186-2, "Digital Signature Standard",
Institute of Standards and Technology, U.S. Department of National Institute of Standards and Technology, U.S.
Commerce, 2000. Department of Commerce, 2000.
[HMAC] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed- [HMAC] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104, February Hashing for Message Authentication", RFC 2104, February
1997. 1997.
[MD5] Rivest, R., "The MD5 Message Digest Algorithm", RFC 1321, [MD5] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
April 1992. April 1992.
[PKCS1] J. Jonsson, B. Kaliski, "Public-Key Cryptography Standards [PKCS1] Jonsson, J. and B. Kaliski, "Public-Key Cryptography
(PKCS) #1: RSA Cryptography Specifications Version 2.1", RFC Standards (PKCS) #1: RSA Cryptography Specifications
3447, February 2003. Version 2.1", RFC 3447, February 2003.
[PKIX] Housley, R., Ford, W., Polk, W. and D. Solo, "Internet X.509 [PKIX] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet
Public Key Infrastructure Certificate and Certificate X.509 Public Key Infrastructure Certificate and
Revocation List (CRL) Profile", RFC 3280, April 2002. Certificate Revocation List (CRL) Profile", RFC 3280,
April 2002.
[SCH] B. Schneier. "Applied Cryptography: Protocols, Algorithms, [SCH] B. Schneier. "Applied Cryptography: Protocols, Algorithms,
and Source Code in C, 2nd ed.", Published by John Wiley & and Source Code in C, 2nd ed.", Published by John Wiley &
Sons, Inc. 1996. Sons, Inc. 1996.
[SHS] NIST FIPS PUB 180-2, "Secure Hash Standard", National [SHS] NIST FIPS PUB 180-2, "Secure Hash Standard", National
Institute of Standards and Technology, U.S. Department of Institute of Standards and Technology, U.S. Department of
Commerce, August 2002. Commerce, August 2002.
[REQ] Bradner, S., "Key words for use in RFCs to Indicate [REQ] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an [RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 25, RFC 2434, IANA Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998. October 1998.
[X680] ITU-T Recommendation X.680 (2002) | ISO/IEC 8824-1:2002, [X680] ITU-T Recommendation X.680 (2002) | ISO/IEC 8824-1:2002,
Information technology - Abstract Syntax Notation One Information technology - Abstract Syntax Notation One
(ASN.1): Specification of basic notation. (ASN.1): Specification of basic notation.
[X690] ITU-T Recommendation X.690 (2002) | ISO/IEC 8825-1:2002, [X690] ITU-T Recommendation X.690 (2002) | ISO/IEC 8825-1:2002,
Information technology - ASN.1 encoding Rules: Specification Information technology - ASN.1 encoding Rules:
of Basic Encoding Rules (BER), Canonical Encoding Rules Specification of Basic Encoding Rules (BER), Canonical
(CER) and Distinguished Encoding Rules (DER). Encoding Rules (CER) and Distinguished Encoding Rules
(DER).
Informative References Informative References
[AEAD] Mcgrew, D., "An Interface and Algorithms for Authenticated [AEAD] McGrew, D., "An Interface and Algorithms for Authenticated
Encryption", RFC 5116, January 2008. Encryption", RFC 5116, January 2008.
[AH] Kent, S., and Atkinson, R., "IP Authentication Header", RFC [AH] Kent, S., "IP Authentication Header", RFC 4302, December
4302, December 2005. 2005.
[BLEI] Bleichenbacher D., "Chosen Ciphertext Attacks against [BLEI] Bleichenbacher D., "Chosen Ciphertext Attacks against
Protocols Based on RSA Encryption Standard PKCS #1" in Protocols Based on RSA Encryption Standard PKCS #1" in
Advances in Cryptology -- CRYPTO'98, LNCS vol. 1462, pages: Advances in Cryptology -- CRYPTO'98, LNCS vol. 1462,
1-12, 1998. pages: 1-12, 1998.
[CBCATT] Moeller, B., "Security of CBC Ciphersuites in SSL/TLS: [CBCATT] Moeller, B., "Security of CBC Ciphersuites in SSL/TLS:
Problems and Countermeasures", Problems and Countermeasures",
http://www.openssl.org/~bodo/tls-cbc.txt. http://www.openssl.org/~bodo/tls-cbc.txt.
[CBCTIME] Canvel, B., Hiltgen, A., Vaudenay, S., and M. Vuagnoux, [CBCTIME] Canvel, B., Hiltgen, A., Vaudenay, S., and M. Vuagnoux,
"Password Interception in a SSL/TLS Channel", Advances in "Password Interception in a SSL/TLS Channel", Advances in
Cryptology -- CRYPTO 2003, LNCS vol. 2729, 2003. Cryptology -- CRYPTO 2003, LNCS vol. 2729, 2003.
[CCM] "NIST Special Publication 800-38C: The CCM Mode for [CCM] "NIST Special Publication 800-38C: The CCM Mode for
Authentication and Confidentiality", Authentication and Confidentiality",
http://csrc.nist.gov/publications/nistpubs/800-38C/ http://csrc.nist.gov/publications/nistpubs/800-38C/
SP800-38C.pdf SP800-38C.pdf
[DES] National Institute of Standards and Technology, "Data [DES] National Institute of Standards and Technology, "Data
Encryption Standard (DES)", FIPS PUB 46-3, October 1999. Encryption Standard (DES)", FIPS PUB 46-3, October 1999.
[DSS-3] NIST FIPS PUB 186-3 Draft, "Digital Signature Standard", [DSS-3] NIST FIPS PUB 186-3 Draft, "Digital Signature Standard",
National Institute of Standards and Technology, U.S. National Institute of Standards and Technology, U.S.
Department of Commerce, 2006. Department of Commerce, 2006.
[ECSDSA] American National Standards Institute, "Public Key [ECDSA] American National Standards Institute, "Public Key
Cryptography for the Financial Services Industry: The Cryptography for the Financial Services Industry: The
Elliptic Curve Digital Signature Algorithm (ECDSA)", ANS Elliptic Curve Digital Signature Algorithm (ECDSA)", ANS
X9.62-2005, November 2005. X9.62-2005, November 2005.
[ENCAUTH] Krawczyk, H., "The Order of Encryption and Authentication [ENCAUTH] Krawczyk, H., "The Order of Encryption and Authentication
for Protecting Communications (Or: How Secure is SSL?)", for Protecting Communications (Or: How Secure is SSL?)",
Crypto 2001. Crypto 2001.
[ESP] Kent, S., and Atkinson, R., "IP Encapsulating Security [ESP] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC
Payload (ESP)", RFC 4303, December 2005. 4303, December 2005.
[FI06] Hal Finney, "Bleichenbacher's RSA signature forgery based on [FI06] Hal Finney, "Bleichenbacher's RSA signature forgery based
implementation error", ietf-openpgp@imc.org mailing list, 27 on implementation error", ietf-openpgp@imc.org mailing
August 2006, http://www.imc.org/ietf-openpgp/mail- list, 27 August 2006, http://www.imc.org/ietf-openpgp/
archive/msg14307.html. mail-archive/msg14307.html.
[GCM] "NIST Special Publication 800-38D DRAFT (June, 2007): [GCM] Dworkin, M., NIST Special Publication 800-38D,
Recommendation for Block Cipher Modes of Operation: "Recommendation for Block Cipher Modes of Operation:
Galois/Counter Mode (GCM) and GMAC" Galois/Counter Mode (GCM) and GMAC", November 2007.
[IKEALG] Schiller, J., "Cryptographic Algorithms for Use in the [IKEALG] Schiller, J., "Cryptographic Algorithms for Use in the
Internet Key Exchange Version 2 (IKEv2)", RFC 4307, December Internet Key Exchange Version 2 (IKEv2)", RFC 4307,
2005. December 2005.
[KEYSIZ] Orman, H., and Hoffman, P., "Determining Strengths For [KEYSIZ] Orman, H. and P. Hoffman, "Determining Strengths For
Public Keys Used For Exchanging Symmetric Keys" RFC 3766, Public Keys Used For Exchanging Symmetric Keys", BCP 86,
April 2004. RFC 3766, April 2004.
[KPR03] Klima, V., Pokorny, O., Rosa, T., "Attacking RSA-based [KPR03] Klima, V., Pokorny, O., Rosa, T., "Attacking RSA-based
Sessions in SSL/TLS", http://eprint.iacr.org/2003/052/, Sessions in SSL/TLS", http://eprint.iacr.org/2003/052/,
March 2003. March 2003.
[MODP] Kivinen, T. and M. Kojo, "More Modular Exponential (MODP) [MODP] Kivinen, T. and M. Kojo, "More Modular Exponential (MODP)
Diffie-Hellman groups for Internet Key Exchange (IKE)", RFC Diffie-Hellman groups for Internet Key Exchange (IKE)",
3526, May 2003. RFC 3526, May 2003.
[PKCS6] RSA Laboratories, "PKCS #6: RSA Extended Certificate Syntax [PKCS6] RSA Laboratories, "PKCS #6: RSA Extended Certificate
Standard", version 1.5, November 1993. Syntax Standard", version 1.5, November 1993.
[PKCS7] RSA Laboratories, "PKCS #7: RSA Cryptographic Message Syntax [PKCS7] RSA Laboratories, "PKCS #7: RSA Cryptographic Message
Standard", version 1.5, November 1993. Syntax Standard", version 1.5, November 1993.
[RANDOM] Eastlake, D., 3rd, Schiller, J., and S. Crocker, "Randomness [RANDOM] Eastlake, D., 3rd, Schiller, J., and S. Crocker,
Requirements for Security", BCP 106, RFC 4086, June 2005. "Randomness Requirements for Security", BCP 106, RFC 4086,
June 2005.
[RFC3749] Hollenbeck, S., "Transport Layer Security Protocol [RFC3749] Hollenbeck, S., "Transport Layer Security Protocol
Compression Methods", RFC 3749, May 2004. Compression Methods", RFC 3749, May 2004.
[RFC4366] Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J., [RFC4366] Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J.,
Wright, T., "Transport Layer Security (TLS) Extensions", RFC and T. Wright, "Transport Layer Security (TLS)
4366, April 2006. Extensions", RFC 4366, April 2006.
[RSA] R. Rivest, A. Shamir, and L. M. Adleman, "A Method for [RSA] R. Rivest, A. Shamir, and L. M. Adleman, "A Method for
Obtaining Digital Signatures and Public-Key Cryptosystems", Obtaining Digital Signatures and Public-Key
Communications of the ACM, v. 21, n. 2, Feb 1978, pp. Cryptosystems", Communications of the ACM, v. 21, n. 2,
120-126. Feb 1978, pp. 120-126.
[SEQNUM] Bellovin. S., "Defending Against Sequence Number Attacks", [SEQNUM] Bellovin, S., "Defending Against Sequence Number Attacks",
RFC 1948, May 1996. RFC 1948, May 1996.
[SSL2] Hickman, Kipp, "The SSL Protocol", Netscape Communications [SSL2] Hickman, Kipp, "The SSL Protocol", Netscape Communications
Corp., Feb 9, 1995. Corp., Feb 9, 1995.
[SSL3] A. Freier, P. Karlton, and P. Kocher, "The SSL 3.0 [SSL3] A. Freier, P. Karlton, and P. Kocher, "The SSL 3.0
Protocol", Netscape Communications Corp., Nov 18, 1996. Protocol", Netscape Communications Corp., Nov 18, 1996.
[SUBGROUP] Zuccherato, R., "Methods for Avoiding the "Small-Subgroup" [SUBGROUP] Zuccherato, R., "Methods for Avoiding the "Small-Subgroup"
Attacks on the Diffie-Hellman Key Agreement Method for Attacks on the Diffie-Hellman Key Agreement Method for
S/MIME", RFC 2785, March 2000. S/MIME", RFC 2785, March 2000.
[TCP] Postel, J., "Transmission Control Protocol", STD 7, RFC 793,
September 1981.
[TIMING] Boneh, D., Brumley, D., "Remote timing attacks are
practical", USENIX Security Symposium 2003.
[TLSAES] Chown, P., "Advanced Encryption Standard (AES) Ciphersuites
for Transport Layer Security (TLS)", RFC 3268, June 2002.
[TLSECC] Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C., and [TCP] Postel, J., "Transmission Control Protocol", STD 7, RFC
Moeller, B., "Elliptic Curve Cryptography (ECC) Cipher 793, September 1981.
Suites for Transport Layer Security (TLS)", RFC 4492, May
2006.
[TLSEXT] Eastlake, D.E., "Transport Layer Security (TLS) Extensions: [TIMING] Boneh, D., Brumley, D., "Remote timing attacks are
Extension Definitions", January 2008, draft-ietf-tls- practical", USENIX Security Symposium 2003.
rfc4366-bis-01.txt.
[TLSPGP] Mavrogiannopoulos, N., "Using OpenPGP keys for TLS [TLSAES] Chown, P., "Advanced Encryption Standard (AES)
authentication", RFC 5081, November 2007. Ciphersuites for Transport Layer Security (TLS)", RFC
3268, June 2002.
[TLSPSK] Eronen, P., Tschofenig, H., "Pre-Shared Key Ciphersuites for [TLSECC] Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C., and B.
Transport Layer Security (TLS)", RFC 4279, December 2005. Moeller, "Elliptic Curve Cryptography (ECC) Cipher Suites
for Transport Layer Security (TLS)", RFC 4492, May 2006.
[TLS1.0] Dierks, T., and C. Allen, "The TLS Protocol, Version 1.0", [TLSEXT] Eastlake, D., 3rd, "Transport Layer Security (TLS)
RFC 2246, January 1999. Extensions: Extension Definitions", Work in Progress,
February 2008.
[TLS1.1] Dierks, T., and E. Rescorla, "The TLS Protocol, Version [TLSPGP] Mavrogiannopoulos, N., "Using OpenPGP Keys for Transport
1.1", RFC 4346, April, 2006. Layer Security (TLS) Authentication", RFC 5081, November
2007.
[X501] ITU-T Recommendation X.501: Information Technology - Open [TLSPSK] Eronen, P., Ed., and H. Tschofenig, Ed., "Pre-Shared Key
Systems Interconnection - The Directory: Models, 1993. Ciphersuites for Transport Layer Security (TLS)", RFC
4279, December 2005.
[XDR] Eisler, M., "External Data Representation Standard", STD 67, [TLS1.0] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
RFC 4506, May 2006. RFC 2246, January 1999.
Credits [TLS1.1] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.1", RFC 4346, April 2006.
Working Group Chairs [X501] ITU-T Recommendation X.501: Information Technology - Open
Systems Interconnection - The Directory: Models, 1993.
Eric Rescorla [XDR] Eisler, M., Ed., "XDR: External Data Representation
EMail: ekr@networkresonance.com Standard", STD 67, RFC 4506, May 2006.
Pasi Eronen Working Group Information
pasi.eronen@nokia.com
Editors The discussion list for the IETF TLS working group is located at the
e-mail address <tls@ietf.org>. Information on the group and
information on how to subscribe to the list is at
<https://www1.ietf.org/mailman/listinfo/tls>
Tim Dierks Eric Rescorla Archives of the list can be found at:
Independent Network Resonance, Inc. <http://www.ietf.org/mail-archive/web/tls/current/index.html>
EMail: tim@dierks.org EMail: ekr@networkresonance.com
Other contributors Contributors
Christopher Allen (co-editor of TLS 1.0) Christopher Allen (co-editor of TLS 1.0)
Alacrity Ventures Alacrity Ventures
ChristopherA@AlacrityManagement.com ChristopherA@AlacrityManagement.com
Martin Abadi Martin Abadi
University of California, Santa Cruz University of California, Santa Cruz
abadi@cs.ucsc.edu abadi@cs.ucsc.edu
Steven M. Bellovin Steven M. Bellovin
Columbia University Columbia University
smb@cs.columbia.edu smb@cs.columbia.edu
Simon Blake-Wilson Simon Blake-Wilson
BCI BCI
EMail: sblakewilson@bcisse.com sblakewilson@bcisse.com
Ran Canetti Ran Canetti
IBM IBM
canetti@watson.ibm.com canetti@watson.ibm.com
Pete Chown Pete Chown
Skygate Technology Ltd Skygate Technology Ltd
pc@skygate.co.uk pc@skygate.co.uk
Taher Elgamal Taher Elgamal
taher@securify.com taher@securify.com
skipping to change at page 99, line 39 skipping to change at page 102, line 29
Anil Gangolli Anil Gangolli
anil@busybuddha.org anil@busybuddha.org
Kipp Hickman Kipp Hickman
Alfred Hoenes Alfred Hoenes
David Hopwood David Hopwood
Independent Consultant Independent Consultant
EMail: david.hopwood@blueyonder.co.uk david.hopwood@blueyonder.co.uk
Phil Karlton (co-author of SSLv3) Phil Karlton (co-author of SSLv3)
Paul Kocher (co-author of SSLv3) Paul Kocher (co-author of SSLv3)
Cryptography Research Cryptography Research
paul@cryptography.com paul@cryptography.com
Hugo Krawczyk Hugo Krawczyk
IBM IBM
hugo@ee.technion.ac.il hugo@ee.technion.ac.il
Jan Mikkelsen Jan Mikkelsen
Transactionware Transactionware
EMail: janm@transactionware.com janm@transactionware.com
Magnus Nystrom Magnus Nystrom
RSA Security RSA Security
EMail: magnus@rsasecurity.com magnus@rsasecurity.com
Robert Relyea Robert Relyea
Netscape Communications Netscape Communications
relyea@netscape.com relyea@netscape.com
Jim Roskind Jim Roskind
Netscape Communications Netscape Communications
jar@netscape.com jar@netscape.com
Michael Sabin Michael Sabin
Dan Simon Dan Simon
Microsoft, Inc. Microsoft, Inc.
dansimon@microsoft.com dansimon@microsoft.com
skipping to change at page 100, line 29 skipping to change at page 103, line 18
Michael Sabin Michael Sabin
Dan Simon Dan Simon
Microsoft, Inc. Microsoft, Inc.
dansimon@microsoft.com dansimon@microsoft.com
Tom Weinstein Tom Weinstein
Tim Wright Tim Wright
Vodafone Vodafone
EMail: timothy.wright@vodafone.com timothy.wright@vodafone.com
Comments Editors' Addresses
The discussion list for the IETF TLS working group is located at the Tim Dierks
e-mail address <tls@ietf.org>. Information on the group and Independent
information on how to subscribe to the list is at EMail: tim@dierks.org
<https://www1.ietf.org/mailman/listinfo/tls>
Archives of the list can be found at: Eric Rescorla
<http://www.ietf.org/mail-archive/web/tls/current/index.html> RTFM, Inc.
EMail: ekr@rtfm.com
Full Copyright Statement Full Copyright Statement
Copyright (C) The IETF Trust (2008). Copyright (C) The IETF Trust (2008).
This document is subject to the rights, licenses and restrictions This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors contained in BCP 78, and except as set forth therein, the authors
retain all their rights. retain all their rights.
This document and the information contained herein are provided on an This document and the information contained herein are provided on an
skipping to change at page 101, line 44 skipping to change at line 4702
attempt made to obtain a general license or permission for the use of attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr. http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at this standard. Please address the information to the IETF at
ietf-ipr@ietf.org. ietf-ipr@ietf.org.
Acknowledgment
Funding for the RFC Editor function is provided by the IETF
Administrative Support Activity (IASA).
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