Security Myths and Passwords

Very good essay by Gene Spafford on passwords...

Policies requiring regular password changes (e.g., monthly) are an example of exactly this form of infosec folk wisdom.

From a high-level perspective, let me observe that one problem with any widespread change policy is that it fails to take into account the various threats and other defenses that may be in place. Policies should always be based on a sound understanding of risks, vulnerabilities, and defenses. “Best practice” is intended as a default policy for those who don’t have the necessary data or training to do a reasonable risk assessment.