Many security policies force users to change passwords within fixed intervals, with the apparent justification that this improves overall security. However, the implied security benefit has never been explicitly quantified. In this note, we quantify the security advantage of a password expiration policy, finding that the optimal benefit is relatively minor at best, and questionable in light of overall costs.

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Keywords Authentication, Guessing attacks, Password aging, Password expiration, Password security in digital systems
Persistent URL
Journal Designs, Codes and Cryptography
Chiasson, S, & Van Oorschot, P. (2015). Quantifying the security advantage of password expiration policies. Designs, Codes and Cryptography, 77(2-3), 401–408. doi:10.1007/s10623-015-0071-9