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TUCoPS :: Password Security :: st04-002.htm

Choosing and Protecting Passwords
US-CERT Cyber Security Tip ST04-002 -- Choosing and Protecting Passwords

National Cyber Alert System
Cyber Security Tip ST04-002     archive

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.

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 password-is 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

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. 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.

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