On Dynamic Subset Difference Revocation Scheme

Subset Difference Revocation (SDR) [8] has been proposed to perform group rekeying in a stateless manner. However, statelessness comes at a cost in terms of storage and message overhead when the number of currently active members is much smaller than the number of potential group members [3]. We propose a dynamic SDR scheme to address these problems. Rather than maintaining a large static key tree that accommodates all potential group members, we use a smaller dynamic key tree for only currently active members. We dynamically assign current members to the positions in the key tree rather than using fixed pre-assignment. The smaller key tree requires less storage and dynamic assignment achieves a smaller rekeying cost. Our evaluation shows that the dynamic scheme significantly improves the performance of SDR, reducing by half the rekey communication cost in the case that the number of the currently active members is much less than the total number of potential members. Compared to SDR in [8], dynamic SDR does not need to know the maximum number of potential group members in advance, a value that can be difficult to estimate in practice.