Selecting a Secure Password

Many password cracking techniques in popular usage today involve "dictionary guessing" where computers are used to automate a trial-and-error guessing process to discover the correct password to an account. Using a large word list or dictionary the attackers try every word or permutation of words in an attempt to guess the password. This process can be surprisingly successful.

As a result you should not use weak passwords that could be feasibly listed in any dictionary, including any foreign language dictionary, such as:

• spelling a dictionary word
• account name backwards
• concatenating one or more dictionary words
• prefixing or suffixing dictionary words with letters or digits  
• Trivial permutations should also be avoided because they are among the first permutations a dedicated attacker will check

Characteristics of good passwords include sufficient:

• Length: Traditional UNIX systems recognize and use the first eight characters of the password so plan on choosing passwords seven to eight characters in length.
   
• Complexity: UNIX passwords are case sensitive, meaning that uppercase and lowercase letters are not the same, and they may also contain unusual characters such as punctuation characters, so plan on using strange or unusual capitalization and characters.
   
• Obscurity: Never use a password that incorporates personal information about yourself that could be easily obtained.

In the book Practical Unix Security, Simson Garfinkel and Gene Spafford offer the following checklist of things to consider when choosing password. To be secure, a password should not be any of the following:

• Your name
• Your spouse's name
• Your parent's name
• Your pet's name
• Your child's name
• Names of close friends or coworkers
• Names of your favorite fantasy characters
• Your boss's name
• Anybody's name
• The name of the operating system you're using
• The hostname of your computer
• Your phone number
• Your license plate number
• Any part of your social security number (or equivalent)
• Anybody's birth date
• Other information that is easily obtained about you
• Words such as "wizard", "guru", "gandalf", and so on
• Any username on the computer in any form (as is, capitalized, doubled, etc)
• A word in the English dictionary
• A word in a foreign dictionary
• A place
• A proper noun
• Passwords of all the same letter
• Simple patterns of letters on the keyboard, like "qwerty"
• Any of the above spelled backwards
• Any of the above followed or prepended by a single digit

The authors continue and state that good passwords are passwords that are difficult to guess. In general, good passwords have the following characteristics:

• Both uppercase and lowercase letters
• Digits and/or punctuation characters as well as letters
• Easy to remember, so they do not have to be written down
• Seven or eight characters long
• Can be typed quickly, so somebody cannot follow what you type by looking over your shoulder

Following a sensible password policy will help ensure that your accounts remain secure.

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