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Choosing Strong Passwords

User Guide to Choosing Good Passwords


This document presents a plain-language guide to security threats posed by password cracking software, and how to apply good password rules to prevent security compromises. It also gives suggestions for choosing good passwords and making them secure and hard to guess.

The Password Management Problem

It's that time again. You've been asked to change the password that gives you access to all your crucial systems and information. Or perhaps you need to enter yet another new password to access yet another application, document, or system.

Choosing Hard to Guess Passwords

It's tempting to pick something easy to remember, like spelling your user name backwards, or child's name, or a word from the dictionary. The problem is, the easier it is to remember, the easier it is for an intruder to steal.

Malicious intruders often gain access to a company's systems by stealing, or cracking, a password and account name, then posing as that user. If the intruder knows you, they can easily gain access by trying password combinations related to your family or hobbies. If they have physical access to your desk or digital assistant, their chances of getting into your accounts are even greater if you've used something personal for your password.

Hackers use readily available software to rapidly enter random dictionary words until they hit pay dirt, and it can take only minutes! The shorter the password, the faster it can be guessed. Even words spelled backwards, rearranged, or including numbers are not safe. A common misconception is that substitutions, such as replacing the letter l or i with the digit 1 will fool password cracking software. Password cracking programs are smart enough to do this too.

Examples of bad passwords include:

  • mydog2
  • bi11smith
  • yromem (memory backwards)
  • win4me

The safest solution for choosing good passwords is to use a randomly generated or seemingly random password that:

  • Is at least 8 characters long, and longer if possible.
  • Contains a mix of upper and lower case letters.
  • Includes numerals, special characters, and punctuation.
  • Is not based on any personal information.
  • Is not based on any dictionary word.

Examples of strong passwords include: 

  • De2#9+vu
  • 5s2d$oiP
  • er?89+TI 

Writing Down Passwords

If you have too many passwords, it is tempting to write them down -- after all, can you really remember 10 different passwords, that change at different times, some of which are rarely used?

Writing down passwords is a serious breach of security, because it means that anyone who can physically get to the piece of paper, sticky note or PDA that contains the password, can also log into systems with your accounts. Should a visiting vendor really be able to sign into the finance application? Should the janitor be able to read your mail?

A better solution is to create a single, strong password, and apply it to all of your login accounts. One password is easier to remember, and is more secure than a post-it note.

Reusing Passwords

Another temptation, when imagination fails, is to reuse old password values when the time comes to change your password. This is also a security problem, since the whole point of a regular password change is to limit the time available to an intruder to crack your password. If an old password is reused, intruders would have more time to crack them. If the old password was already compromised, the new one will compromise your security again.

If you cannot think of a new, secure password -- have a program, like P-Synch, randomly generate one for you.

How to Choose a Good Password

Some security experts recommend using a password based on a mnemonic, such as an easily remembered phrase. For example, take the first letter of a each word in a phrase, then add a few special characters or numbers to it. For example, "lend me your ears" can become "lmye4%". "To be or not to be, that is the question" can become "2Bor!2b?".

This is good technique, but you may need some patience to think up a new phrase every time you change your password -- especially if you have to think of a different password for every system that you log into. This may lead some users to recycle some version of their old password - another security threat.

When to Change Your Password

Perhaps just as important as how to choose a new password is when to do it. New passwords are most easily remembered if you start using them immediately, and use them often. Don't change your password at the end of the day, the end of the week, or before a holiday. Instead, change your password in the morning, at the start of the week. Your mind will be clearer, and frequent use of the new password will reinforce your memory.

Good password practice

Advice on proper password management:

  • never share a computer account,
  • never use the same password for more than one account,
  • never tell a password to anyone, including people who claim to be from customer service or security,
  • never write down a password,
  • never communicate a password by telephone, e-mail or instant messaging,
  • log off before leaving a computer unattended,
  • change your password(s) whenever there is suspicion they may have been compromised,
  • Windows password and application passwords are different,
  • password should be at least alpha-numeric.

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