Password policy

A password policy is a set of rules designed to enhance computer security by encouraging users to employ strong passwords and use them properly. A password policy is often part of an organization's official regulations and may be taught as part of security awareness training. Either the password policy is merely advisory, or the computer systems force users to comply with it. Some governments have national authentication frameworks that define requirements for user authentication to government services, including requirements for passwords.

Typical components of a password policy include:

Many policies require a minimum password length. Eight characters is typical but may not be appropriate. Longer passwords are generally more secure, but some systems impose a maximum length for compatibility with legacy systems.

Some policies suggest or impose requirements on what type of password a user can choose, such as:

Other systems create the password for the users or let the user select one of a limited number of displayed choices.

Password blacklists are lists of passwords that are always blocked from use. Blacklists contain passwords constructed of character combinations that otherwise meet company policy, but should no longer be used because they have been deemed insecure for one or more reasons, such as being easily guessed, following a common pattern, or public disclosure from previous data breaches. Common examples are Password1, Qwerty123, or Qaz123wsx.

Some policies require users to change passwords periodically, often every 90 or 180 days. The benefit of password expiration, however, is debatable. Systems that implement such policies sometimes prevent users from picking a password too close to a previous selection.

This policy can often backfire. Some users find it hard to devise "good" passwords that are also easy to remember, so if people are required to choose many passwords because they have to change them often, they end up using much weaker passwords; the policy also encourages users to write passwords down. Also, if the policy prevents a user from repeating a recent password, this requires that there is a database in existence of everyone's recent passwords (or their hashes) instead of having the old ones erased from memory. Finally, users may change their password repeatedly within a few minutes, and then change back to the one they really want to use, circumventing the password change policy altogether.

The human aspects of passwords must also be considered. Unlike computers, human users cannot delete one memory and replace it with another. Consequently, frequently changing a memorized password is a strain on the human memory, and most users resort to choosing a password that is relatively easy to guess. Users are often advised to use mnemonic devices to remember complex passwords. However, if the password must be repeatedly changed, mnemonics are useless because the user would not remember which mnemonic to use. Furthermore, the use of mnemonics (leading to passwords such as "2BOrNot2B") makes the password easier to guess.

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