High dictionary compression for proactive password checking

The important problem of user password selection is addressed and a new proactive password-checking technique is presented. In a training phase, a decision tree is generated based on a given dictionary of weak passwords. Then, the decision tree is used to determine whether a user password should be accepted. Experimental results described here show that the method leads to a very high dictionary compression (up to 1000 to 1) with low error rates (of the order of 1%). A prototype implementation, called ProCheck, is made available online. We survey previous approaches to proactive password checking, and provide an in-depth comparison.