CHAPTER 6, PART 3
USE OF PUBLIC KEY INFRASTRUCTURE (PKI)
1 BACKGROUND
PKI
is an enabler of trust that provides strong user identification, confidential
communication, data integrity, and evidence for non-repudiation among
individuals that may or may not have had prior knowledge of each other. Non-repudiation provides a
proof-of-participation in an action or transaction by establishing that an
user’s private key was used to digitally sign an electronic business transaction. The trust that PKI facilitates is
enterprise-wide through distinct, yet integrated policies and technology
components. These policies and
components explicitly identify and determine the roles, responsibilities,
constraints, range of use, and services available.
Mathematically
related key pairs both public and private are generated through the use of PKI
technology. While the users’ private
key is safeguarded, their public key is linked to identifying information in a
digitally signed public key certificate certifying their ownership of both
public and private keys. The
certificate and the keys are used in systems and applications to represent the
user or individual identified by the certificate. A user must have one current key pair for encryption and
decryption, and a second key pair for digital signature and signature
verification.
The public key can be accessed by anyone. Only the
person to whom the Private Key is issued has knowledge of this key; it is never
revealed or transmitted. What one key in the pair encrypts, only the other
key can decrypt. The keys are
mathematically related in such a way that it is almost impossible to guess one key from the
other. For example, a user (BOB) can
send a message to another user (CAROL) by encrypting the message with CAROL's
public key because only CAROL holds the private key to decrypt it. For authenticity
(digital signature), BOB can send CAROL
a
message encrypted with his private key. CAROL can be certain it came from BOB because it can be decrypted only
by using BOB's public key. The identity of BOB is verifiable because
only BOB has access to his private key.
A digital
signature is an electronic signature that can be used to authenticate the
identity of the sender of a message or the signer of a document. Besides being easily transportable, it can
also ensure that the content of the message or document that has been sent is
unchanged. When time-stamped, the
ability to ensure that the original signed message arrived means that the sender
cannot easily repudiate it later.
Certification Authorities (CAs) represent the people, processes, and tools to create digital certificates that securely bind the names of users to their public keys. The following parties rely on the appropriate level of trust with respect to the creation and use of public key certificates: the individual Subscriber or entity identified by the certificate; the Certification Authority who issues the certificate; the Registration or Validation Authority that provides certificate validation services in certain implementations; and the Relying Party (company, agency or individual) relying on the certificate.
As
long as users trust a CA and its policies for issuing
and
managing certificates, they can trust certificates issued by the CA. The CA investigates individuals and verifies
their identity, binding that identity to
the public key and verifying that the individual has the private key. Levels of trust are
placed on the level of identification
and verification required by the certificate level (i.e. low, medium, high). The FBCA will
assist in the interoperability
between
CAs. In this process, the FBCA will establish level of assurance translations between agencies.
Interoperability is a critical issue for Public Key Infrastructures. Interoperability deals with interaction between systems directly supporting and/or consuming PKI-related services (component-level interoperability), compatibility between two peers, regardless of the supplier of the application or any ancillary infrastructure components used to support the application (application-level interoperability), and issues and options associated with achieving interoperability between two otherwise isolated PKI domains (inter-domain interoperability).
Traditional PKI architectures fall into one of three configurations: a single CA, a mesh of CAs, or a hierarchy of CAs. The PKI architecture that contains a single CA provides the PKI services for all the users of the PKI and its users place their trust in the only CA. Mesh PKIs have multiple trust points.
A hierarchy of CAs has two levels: the Root CA and subordinate CAs. The Root CA is responsible for administering the policy and procedures for the entire PKI system and the Subordinate CAs are responsible for binding users to their public key. The Root CA is the PKI component that is able to facilitate the integration of the USDA member agencies separate PKI applications. From a larger context, this architecture will facilitate secure interoperability for such technologies as virtual private networks, database access, authentication/access control to remote computing resources, and future PKI applications.
As more USDA agencies develop CAs whose processes have been certified, the Cyber Security Office reserves the right to establish a PKI Root CA at the Department level. Agencies can also outsource their CA services, but must comply with this policy.
USDA’s PKI efforts will further be enhanced by its ability to interoperate with disparate PKI domains (cross-certification), an inherent feature to providing electronic government services across the department. Cross-certification provides a trust framework by evaluating digital credentials against a set standard. The Federal Bridge Certification Authority (FBCA) supports interoperability among Federal Agency PKI domains in a peer-to-peer fashion. The policies and procedures of the FBCA are governed by the Federal PKI Policy Authority, which has responsibility for mapping a CA’s policies and practices against the FBCA standard.
2 Policy
All agencies and
mission areas whose major support systems have a security requirement for
non-repudiation will use digital signature.
It
is the policy of the United States Department of Agriculture to encourage the
use of PKI in satisfying system security requirements for non-repudiation. Agencies must satisfy the following
procedural requirements prior to deployment of a Public Key Infrastructure.
Policy
Exception Requirements –
Agencies will submit all policy exception requests directly to the ACIO for
Cyber Security. Exceptions to policy
will be considered only in terms of implementation timeframes; exceptions will
not be granted to the requirement to conform to this policy. Exceptions that are approved will be interim
in nature and will require that each agency report this Granted Policy
Exception (GPE) as a Plan of Action & Milestone (POA&M) in their FISMA
reporting, with a GPE notation, until full compliance is achieved. Interim exceptions expire with each
fiscal year. Compliance exceptions that
require longer durations will be renewed on an annual basis with a updated
timeline for completion. CS
will monitor all approved exceptions.
3 PROCEDURES
a Develop
a business case model for PKI to determine its applicability in the
organization’s business strategies. A
business case outlines and justifies the total cost of developing a PKI,
including any associated IT development costs.
It also determines what level of security is appropriate, identifies
risks, determines benefits, legal and regulatory compliance constraints and
identifies possible alternatives.
b Devise
a PKI Strategy and Implementation Plan that will serve as a roadmap for
deployment. This plan should
essentially define: 1) how the PKI will be operated; 2) how trust will be passed
between entities; 3) the PKI architecture and its components; 4) how
applications are to be PKI-enabled; 5) how the PKI will be tested and
supported; and 6) a detailed project plan.
c Conduct
a risk analysis to review the existing information security infrastructure and
to assess the readiness of the targeted PKI organization. Security in any system should be
commensurate with its risks. The risk
analysis forms a more objective basis for determining which security controls
are appropriate and cost effective.
d Develop
a Certificate Policy that maps to the FBCA certificate policy. The certificate policy is a descriptive
document that identifies how the PKI environment will operate and it supports
the creation/use of a certificate. This policy is the primary vehicle for
establishing whether a certificate is fit for the purpose for which it is
presented. The agency must explicitly
describe any liability or financial responsibility accepted from the use of these
certificates.
e Establish a Certification
Practice Statement. The CPS is the
statement of practices that a certification authority employs in issuing
certificates and contains much greater detail than a Certificate Policy. Any agreement signed between certificate
authorities, government entities, or third party contractors must be approved
by the Office of the General Counsel.
f Devise a Subscriber
Agreement. The subscriber agreement
requires subscribers to accept certain responsibilities and obligations with
respect to the use of the certificate or with respect to the protection of the
private key corresponding to the public key contained in the certificate. It also establishes subscriber liability and
also serves as an enforcement mechanism in the event those obligations are
breached.
g Establish
a compliance review requirement that will include but is not limited to a
compliance audit of: the agency Certificate Policy, the operational compliance
audit of the Certificate Practice Statements, and the actual operation of the
PKI.
h
Support the recovery of
decryption keys for information as it
traverses
the network and while at rest. A key
recovery policy will be established by each agency.
i Develop
and maintain the Program and
System Security Plan in accordance OCIO Interim Guidance CS-002, Information
Cyber Security Plan Call, relevant laws, regulations and guidelines. (See
publications cited in the Reference Section)
j Audit
PKIs annually in accordance with USDA requirements.
k Meet
USDA physical security requirements for controlling and securing IT restricted
space.
l Require
all personnel that have access to the CA to obtain a high security clearance.
(OGC wants this clarified as to type of clearance)
m Implement
an effective configuration management program and develop site configuration
management plans and procedure documents.
n Maintain
USDA’s C2 Level of Trust security controls for all security devices used
for creation, delivery, and authentication.
USDA’s C2 security is a standard applied at the operating system level
to limit risk to the digital certificates used in PKI technology. Only individuals who have an “ongoing
business need” would have access to PKI technology. This standard assures that individuals without a legitimate need
are not given access to PKI data. All
operating systems containing these devices will be in a hardened state.
o Support
interoperability through the cross-certification of external certificates. Agencies may elect to interoperate without using the FBCA. Those agencies that elect to do so will
employ levels of assurance that mimic those set forth in FBCA Certificate
policy.
p Scan all security devices monthly.
q Require
only in-person proofing before a Registration Authority, Local Registration
Authority (LRA), Trusted Agent or an entity certified by a State or Federal
Agency as being authorized to confirm identities for the issuance of
certificates for the purpose of using digital signature.
r Use
the X.509 Version 3 Standard for all Digital Certificates and the X.509 version
2 standard for Certificate Revocation Lists used within USDA. A X.500 Distinguished Name (DN) naming
convention that is consistent among all USDA agencies will be used, but must be
flexible enough to allow individual agencies to make use of existing identification
information.
s Use
only FIPs 140-2 compliant cryptographic algorithms.
The word
“assurance” means how well a Relying Party can be certain of the identity
binding between the public key and the individual whose subject name is cited
in the certificate. USDA will use 4 assurance levels based on
the sensitivity of the data being processed.
The lowest levels, basic and rudimentary, will not be used for sensitive
information nor use digital signature to satisfy non-repudiation. The
following assurance levels will be used for these certificates:
Requirements and Specifications
|
|||
Digital Certificate Type |
Registration and Application |
Private Key Generation and Storage
Options |
Recommended Reliance Limit |
High Assurance Digital Certificate |
|
Select One:
|
§
Sensitive
but Unclassified Data §
Threats to data high;
consequences of security failure
high; §
High Dollar value transactions;
high fraud risk; risk of malicious access to private data high |
Medium Assurance Digital Certificate NOTE: MEDIUM
ASSURANCE CERTIFICATES MAY ONLY BE USSUED BY HIGH LEVEL AGENCY LOCAL
REGISTRATION AUTHORITIES AND ALL PRIVATE KEYS MUST BE STORED ON FIPS STANDARD
SMART CARDS/TOKENS AT THE TIME OF USE. |
|
Select One:
|
§
Sensitive
but Unclassified Data §
Risk/consequence
of data compromise moderate; includes substantial $ value transactions &
risk of fraud; risk of malicious access to private data substantial |
Basic Assurance Digital Certificate (Will not support non-repudiation) |
|
Select One:
|
§
Sensitive Data §
Risk/consequence of compromise
not major; risk of malicious access to private data not high |
Rudimentary Assurance Digital Certificate (will not support
non-repudiation) |
|
|
§
Unclassified Data §
Risk/consequence of compromise
not major §
Insufficient for transactions
requiring confidentiality and authentication Used primarily to provide data
integrity to the information being signed |
The PKI must go
through a formal certification and accreditation (C&A) process before it
can be deployed in the operational environment. An independent Third Party must certify all USDA PKI
systems. System certification is a
formal procedure for testing security safeguards in a computer system or major
application to determine if they meet applicable requirements and specifications. System accreditation is the formal
authorization by a management official for system operation and an explicit acceptance of the associated risk. The management official ensures that all
equipment resident on the network under his authority is operated using
approved security standards. All
C&A evaluations or annual reviews must be conducted by a third party who
must have not developed the present PKI solution or have any other business
relationship.
If the Office of Cyber Security establishes a Root Certificate
Authority at the department level, those agencies whose CAs were created before
the USDA Root Certificate Authority was operational, will be “grand-fathered”
into the USDA PKI hierarchy until the agency’s certificates issued during that
time have expired.
4 RESPONSIBILITIES
a The Associate CIO for Cyber Security
will:
(1)
Periodically
review and update this notice as required;
(2)
Provide
security standards for implementation of PKI in USDA information technology
environments that handle sensitive data and require non-repudiation;
(3)
Review
agency plans to implement this policy;
(4)
Review
requests for exceptions or exceptions to this policy; and
(5) Conduct reviews of USDA agencies and
mission areas to ensure compliance with this policy.
b The Associate CIO for
Information Resources Management (IRM) will:
(1)
Support the
policy and procedures contained in this
chapter
to ensure that appropriate security protection
is provided to all
USDA managed networks, systems and servers; and
(2)
Receive, review
and coordinate a response with the Associate CIO for Cyber Security to any
exception requests for exceptions to this policy.
c Agency Chief Information Officer
will:
(1)
Ensure the
provisions of this policy are implemented;
(2) Assure that the requirements of PKI
policy are satisfied prior to deployment of this technology on any system;
(3)
Ensure that a back up of the
encryption private key(s) is obtained that will be securely stored so encrypted
documents may be historically retrieved.
The signing private key will exist only on the key token or profile issued to the individual. The solution must provide a means for
archival of private decryption keys, and support for the recovery of a private
decryption key on request;
(4)
Ensure that
agency server administrators, staff offices responsible for server
administration, ISSPMs and security staff are acquainted and comply with the
provisions of OCIO Cyber Security Guidance Regarding C2 Controlled Access
Protection (CS-013 dated 3/6/02);
(5) Assure that agency server administrators,
staff offices responsible for server administration, information system
security program managers and security staff are trained to implement and,
maintain PKI at a functional C2 level and fully understand the ongoing
responsibilities to preserve that level of server security.
d Agency
Information Systems Security Program Manager will:
(1)
Monitor all agency PKI installations to ensure that
the
provisions of this policy are followed;
(2)
Coordinate with agency server administrators to ensure
that
precautions are taken to properly preserve the required level of server
security;
(3)
Coordinate with agency personnel to ensure proper
certification
and accreditation occur on all PKI systems
prior
to deployment;
(4)
Coordinate with agency system owners to ensure that
PKI
private key pairs are properly stored.
e System Administrators/Security
Administrators responsible for server administration will:
(1)
Monitor
vendor release notes for new security patches, service packs, software upgrades
and updates;
(2)
Follow
internal configuration management practices in installing security patches and
updates; and
(3)
Maintain a
configuration control manual that documents all changes to the servers with
sensitive information.
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