Abstract: Based on the analysis of the tree-based authenticated group key agreement protocol AGKA, we find a weakness in the protocol which is caused by teh different priority of the group member in the negotiation. The weakness indicates that the prior group members may use different shared keys to cheat other members in the same group. Based on the above analysis, a novel authenticated group key agreement protocol, named the EAGKA, is proposed based on the verification of the DLE protocol. With the EAGKA, all members are absolutely equal and the weakness of AGKA is overcome. It can be applied in groups that require high security.

Key words: group key agreement, DLE protocol, AGKA, EAGKA