Secure verifier-based three-party password-authenticated key exchange

In order to secure large-scale peer-to-peer communication system, Chien recently presented a three-party password authenticated key exchange protocol using verifiers to reduce the damages of server corruption. In this paper, we first show his protocol is still vulnerable to a partition attack (offline dictionary attack). Thereafter we propose an enhanced verifier-based protocol that can defeat the attacks described and yet is reasonably efficient. Furthermore, we can provide the rigorous proof of the security for it.