How To Choose Good Passwords
From Symantec: http://www.symantec.com/connect/articles/simplest-security-guide-better-password-practices
Let’s begin with what NOT to do when choosing passwords.
No Dictionary Words, Proper Nouns, or Foreign Words
Password cracking tools are very effective at processing large quantities of letter and number combinations until a match for the password is found, as such users should avoid using conventional words as passwords. By the same token, they should also avoid regular words with numbers tacked onto the end and conventional words that are simply written backwards, such as ‘nimda’. While these may prove to be difficult for people to figure out, they are no match for the brute force attacks of password cracking tools.
No Personal Information
One of the frustrating things about passwords is that they need to be easy for users to remember. Naturally, this leads many users to incorporate personal information into their passwords. However, as is discussed in the Social Engineering Fundamentals, it is alarmingly easy for hackers to obtain personal information about prospective targets. As such, it is strongly recommended that users not include such information in their passwords. This means that the password should not include anything remotely related to the user’s name, nickname, or the name of a family member or pet. Also, the password should not contain any easily recognizable numbers like phone numbers or addresses or other information that someone could guess by picking up your mail.
Length, Width and Depth
A strong, effective password requires a necessary degree of complexity. Three factors can help users to develop this complexity: length, width & depth. Length means that the longer a password, the more difficult it is to crack. Simply put, longer is better. Probability dictates that the longer a password the more difficult it will be to crack. It is generally recommended that passwords be between six and nine characters. Greater length is acceptable, as long as the operating system allows for it and the user can remember the password. However, shorter passwords should be avoided.
Width is a way of describing the different types of characters that are used. Don’t just consider the alphabet. There are also numbers and special characters like ‘%’, and in most operating systems, upper and lower case letters are also known as different characters. Windows, for example, is not always case sensitive. (This means it doesn’t know the difference between ‘A’ and ‘a’.) Some operating systems allow control characters, alt characters, and spaces to be used in passwords. As a general rule the following character sets should all be included in every password:
uppercase letters such as A, B, C;
lowercase letters such as a, b,c;
numerals such as 1, 2, 3;
special characters such as $, ?, &; and
alt characters such as µ, £, Æ. (Cliff)
Depth refers to choosing a password with a challenging meaning – something not easily guessable. Stop thinking in terms of passwords and start thinking in terms of phrases. “A good password is easy to remember, but hard to guess.” (Armstrong) The purpose of a mnemonic phrase is to allow the creation of a complex password that will not need to be written down. Examples of a mnemonic phrase may include a phrase spelled phonetically, such as ‘ImuKat!’ (instead of ‘I’m a cat!’) or the first letters of a memorable phrase such as ‘qbfjold*’ = “quick brown fox jumped over lazy dog.”
What may be most effective is for users to choose a phrase that is has personal meaning (for easy recollection), to take the initials of each of the words in that phrase, and to convert some of those letters into other characters (substituting the number ‘3’ for the letter ‘e’ is a common example). For more examples, see the University of Michigan’s Password Security Guide.
All of the good password cracking programs include foreign words, backwards words, etc. And the easiest way to steal a password is by asking for it, so it’s simpler to never give it away.