An Offline Dictionary Attack against a Three-Party Key Exchange Protocol

Despite all the research efforts made so far, the design of protocols for password-authenticated key exchange (PAKE) still remains a non-trivial task. One of the major challenges in designing such protocols is to protect low-entropy passwords from the notorious dictionary attacks. In this work, we revisit Abdalla and Pointcheval’s three-party PAKE protocol presented in Financial Cryptography 2005, and demonstrate that the protocol is vulnerable to an off-line dictionary attack whereby a malicious client can find out the passwords of other clients.