To know what makes a password good, it is necessary to know what makes a password bad. A bad password is one that is easily guessed by a stranger, a friend, or a computer program. Examples of bad passwords are:

• License plate numbers
• Dates
• Words found in any dictionary, including languages other than English, slang, jargon, abbreviations, proper names, etc.
• Combinations of dictionary words
• Dictionary words spelled backwards
• Numbers
• Any personal information

What is left? With all of these restrictions, it is still possible to come up with a password that is easy to remember, yet cryptic enough not to be guessable. One of the most popular ways to select a good password that is easily remembered is to take a phrase or quote that you can remember.

A Unix system password should be at least 6 characters long and include at least one upper case letter (A-Z), digit (0-9) or punctuation character (such as . , or - ). Passwords will not be accepted in Unix if:

• they are less than 6 characters long
• match anything in your Unix account information, such as your login name or an item from your "finger" data
• are found in the system's spelling dictionary
• have more than 2 repeated characters; thus "aaa" would be rejected.
• names of people and places
• any password that has one or more illegal characters in it. A ^ before a character means that the Ctrl key is held at the same time as the specified character. Illegal characters include: ^c, ^d, ^g, ^h (or Backspace), ^i (or Tab), ^j, ^m, ^o, ^r, ^s, ^q, ^y, ^z, ^\, ^, Delete, @, and #.

Note: Unix administrators randomly run a program called crack. The purpose of this program is to test all the user passwords to see if they are too easily guessed. If it finds a password that is too easy, the Unix account is automatically suspended until the user changes his password.

How to Choose a Good Password:

1. Choose a short, simple phrase, six to eight words, that will be easy for you to remember.
   I like to eat green peas.
2. If any of the words are homonyms for other letters or symbols, write them with those symbols (e.g. are =r, you = u, two = 2)
   I like 2 eat green peas.
3. Now, make an acronym. Drop all but the first letter of each word.
   Il2egp
4. Capitalize arbitrarily, but with restraint, try to keep the password easy to remember.
   iL2eGp
5. Add a punctuation mark or two to bring your password's length to seven or eight characters.
   iL2eGp!