Join-Tree-Based Contributory Group Key Management

With emergence of group-oriented applications needing content confidentiality, secure group communications have drawn more attention. To provide this service in large groups with highly dynamic memberships, a secure group key management efficient in key establishment and update is the foundation. In this paper, we present a join-tree-based contributory group key management (JDH) to achieve better time efficiency, and propose using the notion "sequential exponentiations" as the evaluation metric for time efficiency. First, a new key tree topology comprised of main tree and join tree is put forward, with the join tree locating close to the root of the key tree and serving as the temporary buffer for sequential joining users. Then, a new join algorithm in the join tree is presented to reduce the time complexity. Last, optimal capacity of the join tree is selected through an optimization method. Theoretical analysis shows that the asymptotic average join time is sharply reduced to from previous, where is the group size. Our analytical comparison with existing managements and experiments demonstrate that JDH is time and communication efficient in group key establishment and update.