An Efficient Conference Key Updating Scheme with the Knowledge of Group Dynamics

Conference key management requires relatively heavy-weight modular exponentiation operations and additional communications among group members. So time efficiency of key update for conference key management is the key problem many literatures strived to address. In this paper, we propose a Huffman-based join-exit-tree (HJET) key agreement to achieve better time efficiency in key update. Compared with JET scheme of Mao et al., HJET has two major improvements. First, the join algorithm inserting the new node into the root of the join tree makes the join cost minimal and constant. Second, Huffman coding is used to form the exit tree with the information of users' withdrawal probabilities, and therefore has optimal average leave cost. Performance analysis and simulation results demonstrate that HJET is efficient in key update and achieves the asymptotic time cost of O(1) for join event and nearly O(1) for leave events.