On the Security of a Group Key Agreement Protocol and Its Improvement with Pairings

In the paper, we analyze the security vulnerability of the key agreement protocol proposed by Lee et al.'s. We present a forgery attack to their protocol. In this attack, the adversary can modify the signed message and forge a new signature, which can pass the verification. Then, we propose a new group key agreement protocol, which overcomes this security drawback. The new protocol can be proved to be secure under Elliptic Curve Discrete Logarithm Problem, Bilinear Computational Diffie–Hellman Problem and Square-Exponent Problem. On the other hand, in the new protocol, only three pairing operations are used, so it is more efficient. Our protocol is also a contributory group key agreement protocol.