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 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

[US-CERT]