Due to the explosive development of emerging applications such as, Multicast service, Pay-TV systems, Teleconference, and Collaborate tasks, engineers have proposed many conference key distribution mechanisms. Hwang et al. recently proposed an efficient group key exchange method 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 protocol does not preserve the forward and backward secrecy. We therefore propose an improved version which not only inherits the advantage of previous literature, but also provides the forward and backward secrecy among group members. Besides, we give a formal analysis to the correctness of the new method based on BAN authentication logic.