A group key agreement protocol based on ECDH and short signature

Abstract

A group key agreement protocol allows a set of users to establish a common session key over an open network. A dynamic contributory group key agreement (DCGKA) protocol generates a session key based on contributions of all group members and allows a member to dynamically join or leave this group. Although current DCGKA can resist passive attacks, it cannot resist positive attacks like the man-in-the-middle (MITM) attack. In this paper, we propose a dynamic contributory Group Key Agreement protocol by using Short Signature (called GKA-SS) which uses bilinear map to accomplish the signature and the verification processes. The formal security proof shows that our protocol can resist both active and passive attacks under random oracle model. The informal security analysis indicates that our protocol can obtain backward secrecy, forward secrecy, etc. Besides, we analyze the communication and computation cost of our protocol and simulate it with pypbc library. As compared with TGECDH, our protocol is 2.4 times faster in join phase and 29 times faster in leave phase, when p is 512 bits, q is 160 bits and group size is 256.