On the forward and backward secrecy of HLL group key exchange mechanism

Due to the explosive development of several emerging applications such as, multicast communication service, Pay-TV, teleconference, and collaborate tasks, mechanisms of group key exchange have attracted a lot of attentions. In 2004, Hwang et al. proposed an efficient group key exchange mechanism for providing secure multicast communications, which is a transformation from the two-party key exchange protocol to the group one. In this article, we point out that Hwang et al.´s proposed mechanism does not preserve the forward secrecy and the backward secrecy. We consequently propose an improved version to repair the security flaws of Hwang et al.´s group key exchange mechanism.