Editing Password policy (section)

===Password duration===
Some policies require users to change passwords periodically, often every 90 or 180 days. The benefit of password expiration, however, is debatable.<ref name=WEB>
{{cite web
 |url         = https://www.cesg.gov.uk/articles/problems-forcing-regular-password-expiry
 |title       = The problems with forcing regular password expiry
 |date        = 15 April 2016
 |work        = IA Matters
 |publisher   = CESG: the Information Security Arm of GCHQ
 |accessdate  = 5 Aug 2016
 |url-status     = dead
 |archiveurl  = https://web.archive.org/web/20160817223701/https://www.cesg.gov.uk/articles/problems-forcing-regular-password-expiry
 |archivedate = 17 August 2016
}}
</ref><ref>{{cite web|url=http://www.cerias.purdue.edu/site/blog/post/password-change-myths/|title=Security Myths and Passwords
|publisher=CERIAS|date=April 19, 2006 |author=spaf}}</ref> Systems that implement such policies sometimes prevent users from picking a password too close to a previous selection.<ref>{{cite web |url=https://technet.microsoft.com/en-us/library/ff741764.aspx |title=Tip: Best Practices for Enforcing Password Policies |publisher=[[Microsoft]] |access-date=2018-03-01}}</ref>

This policy can often backfire. Some users find it hard to devise "[[Password strength|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 [[Cryptographic hash function|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 (See [[Password fatigue]]). 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.

Administration factors can also be an issue. Users sometimes have older devices that require a password that was used before the password duration expired.{{clarify|date=December 2015}} In order to manage these older devices, users may have to resort to writing down all old passwords in case they need to log into an older device.

Requiring a very strong password and not requiring it be changed is often better.<ref>{{cite conference | url=http://cs.unc.edu/~fabian/papers/PasswordExpire.pdf | title=The Security of Modern Password Expiration: An Algorithmic Framework and Empirical Analysis | date=2010 | author=Yinqian Zhang|author2=Fabian Monrose|author3=Michael K. Reiter | pages=176–186 | conference=Proceedings of the 17th ACM conference on Computer and communications security | doi=10.1145/1866307.1866328 | location=New York, NY, US}}</ref> However, this approach does have a major drawback: if an unauthorized person acquires a password and uses it without being detected, that person may have access for an indefinite period.

It is necessary to weigh these factors: the likelihood of someone guessing a password because it is weak, versus the likelihood of someone managing to steal, or otherwise acquire without guessing, a stronger password.

[[Bruce Schneier]] argues that "pretty much anything that can be remembered can be cracked", and recommends a scheme that uses passwords which will not appear in any dictionaries.<ref>{{cite web|url=https://www.schneier.com/blog/archives/2014/03/choosing_secure_1.html|title=Choosing Secure Passwords|via=Schneier on Security|publisher=BoingBoing|date=March 2014}}</ref>