| Choosing and Protecting Passwords
Passwords are a common form of authentication and are often the only
barrier between a user and your personal information. There are
several programs attackers can use to help guess or "crack" passwords,
but by choosing good passwords and keeping them confidential, you can
make it more difficult for an unauthorized person to access your
information.
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Why do you need a password?
Think about the number of PIN numbers, passwords, or passphrases you
use every day: getting money from the ATM or using your debit card in
a store, logging on to your computer or email, signing in to an online
bank account or shopping cart...the list seems to just keep getting
longer. Keeping track of all of the number, letter, and word
combinations may be frustrating at times, and maybe you've wondered if
all of the fuss is worth it. After all, what attacker cares about your
personal email account, right? Or why would someone bother with your
practically empty bank account when there are others with much more
money? Often, an attack is not specifically about your account but
about using the access to your information to launch a larger
attack. And while having someone gain access to your personal email
might not seem like much more than an inconvenience and threat to your
privacy, think of the implications of an attacker gaining access to
your social security number or your medical records.
One of the best ways to protect information or physical property is
to ensure that only authorized people have access to it. Verifying
that someone is the person they claim to be is the next step, and this
authentication process is even more important, and more difficult, in
the cyber world. Passwords are the most common means of
authentication, but if you don't choose good passwords or keep them
confidential, they're almost as ineffective as not having any password
at all. Many systems and services have been successfully broken
into due to the use of insecure and inadequate passwords, and some
viruses and worms have exploited systems by guessing weak passwords.
How do you choose a good password?
Most people use passwords that are based on personal information and
are easy to remember. However, that also makes it easier for an
attacker to guess or "crack" them. Consider a four-digit PIN
number. Is yours a combination of the month, day, or year of your
birthday? Or the last four digits of your social security number? Or
your address or phone number? Think about how easily it is to find
this information out about somebody. What about your email
passwordis it a word that can be found in the dictionary? If so, it
may be susceptible to "dictionary" attacks, which attempt to guess
passwords based on words in the dictionary.
Although intentionally misspelling a word ("daytt" instead of
"date") may offer some protection against dictionary attacks, an even
better method is to rely on a series of words and use memory
techniques, or mnemonics, to help you remember how to decode it. For
example, instead of the password "hoops," use "IlTpbb" for "[I] [l]ike
[T]o [p]lay [b]asket[b]all." Using both lowercase and capital letters
adds another layer of obscurity. Your best defense, though, is to use
a combination of numbers, special characters, and both lowercase and
capital letters. Change the same example we used above to "Il!2pBb."
and see how much more complicated it has become just by adding numbers
and special characters.
Don't assume that now that you've developed a strong password you
should use it for every system or program you log into. If an attacker
does guess it, he would have access to all of your accounts. You
should use these techniques to develop unique passwords for each of
your accounts.
Here is a review of tactics to use when choosing a password:
- Don't use passwords that are based on personal information that can be easily accessed or guessed
- Don't use words that can be found in any dictionary of any language
- Develop a mnemonic for remembering complex passwords
- Use both lowercase and capital letters
- Use a combination of letters, numbers, and special characters
- Use different passwords on different systems
How can you protect your password?
Now that you've chosen a password that's difficult to guess, you have
to make sure not to leave it someplace for people to find. Writing it
down and leaving it in your desk, next to your computer, or, worse,
taped to your computer, is just making it easy for someone who has
physical access to your office. Don't tell anyone your passwords, and
watch for attackers trying to trick you through phone calls or email
messages requesting that you reveal your passwords.
If your Internet service provider (ISP) offers choices of
authentication systems, look for ones that use Kerberos,
challenge/response, or public key encryption rather than simple
passwords (see Understanding
ISPs and Supplementing
Passwords for more information). Consider challenging service
providers who only use passwords to adopt more secure methods.
Also, many programs offer the option of "remembering" your
password, but these programs have varying degrees of security
protecting that information. Some programs, such as email clients,
store the information in clear text in a file on your computer. This
means that anyone with access to your computer can discover all of
your passwords and can gain access to your information. For this
reason, always remember to log out when you are using a public
computer (at the library, an Internet cafe, or even a shared computer
at your office). Other programs, such as Apple's Keychain and Palm's
Secure Desktop, use strong encryption to protect the
information. These types of programs may be viable options for
managing your passwords if you find you have too many to remember.
There's no guarantee that these techniques will prevent an attacker
from learning your password, but they will make it more difficult.
Authors: Mindi McDowell, Jason Rafail, Shawn Hernan
Copyright 2004 Carnegie Mellon University. Terms of use
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Last
updated January 31, 2007
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