A General Way to Break Hash-based Challenge-and-Response

Hash-based challenge-and-response protocols are widely used as an authentication scheme in network applications. The authenticator sends a random string as a challenge to the peer, the peer generates a response with a hash function on a pre-shared password combined the received challenge. In this paper, we propose a general and efficient way to break some prevalent hash-based challenge- and-response protocols in use. These protocols are vulnerable to the chosen challenge attack launched by a malicious user, who impersonates the server. We first generate a rainbow table containing hash values of all possible passwords, which is produced by hashing a pre-chosen challenge concatenated with all possible password candidates. Second, we impersonate the authenticator and send the pre-chosen challenge to the peer. Finally, we look up in the rainbow table for the received response from the peer to crack the password. With this tactic, we can do the cost consuming pre-computation once, and then we can always use it to recover all of the peer´s passwords with only one additional on-line query.