A proposed password is decomposed into basic components to determine and score transitions between the basic components and create a password score that measures the strength of the proposed password based on rules, such as concatenation, insertion, and replacement. The proposed password is scored against all known words, such as when a user is first asked to create a password for an account or access. The proposed password can also be scored against one or more previous passwords for the user, such as when the user is asked to change the user's previous password, to determine similarity between the two passwords.