Security analysis and improvements of a communication-efficient three-party password authenticated key exchange protocol

Abstract

Three-party password-authenticated key exchange (3PAKE) protocols allow two clients to establish secure communication channels over a public network merely by sharing a human-memorable (low-entropy) password with a trusted server. In this paper, we first show that the 3PAKE protocol introduced by Chang, Hwang, and Yang is insecure against even passive attackers. Thereafter, we propose two kinds of improvement that can remedy the security flaw in their protocol. Finally, we present simulations to measure the execution time to show the efficiency of our two improvements.