Preventing Weak Password Choices

A common problem with systems that use passwords for authentication results when users choose weak passwords. Weak passwords are passwords that arc easy to guess, or likely to be found in a dictionary attack. Thus, the choice of weak passwords may lead to system compromisation. Methods exist to prevent users from selecting and using weak passwords. One common method is to compare user choices against a list ofunRcceptable words. The problem with. this approach is the amount of space required to store even a modest-sized dictionary of prohibited password choices. This paper describes a space-efficient method of storing a didionary of words that are not allowed as password choices. Lookups in the didionary are 0(1) (constant time) no maHer how many words are in the didionary. The mechanism described has other interesting features, a few of which are described here.