Improvement of an Efficient Identity-Based Group Key Agreement Protocol

In 2009, Zeng Ping et al. proposed a new Group Key Agreement protocol Based on the ID-AGKA protocol which uses full binary tree structure and each tree node represents a user. Their protocol support users to join or leave the group at any time and the session key will be changed with the users´ dynamic changes. In this paper, we point out that Zeng Ping et al.´s Group Key Agreement protocol is non-authenticated and easy to be forged or modified. Then we give a method that attacker can force all group members accepted the modified session private key in BR security model. So, It means that the Zeng Ping et al.´s Protocol can not meet the attribute of implicit key authentication and key control. Finally, we propose an improved protocol to overcome this problem.