An Adaptive Hybrid Rekeying Protocol for Dynamic Multicast Groups

In secure multi-party communications, the Logical Key Hierarchy scheme has been proved to be communication optimal for large groups. However, this scheme still suffers from an expensive rekeying cost when the group is very dynamic. To reduce the rekeying cost, Zhu et al. suggested to partition the logical key tree in two sub-trees based on the duration of each member in the multicast group. Although this scheme reduces the rekeying cost for long-duration members, the key server still needs to send a potentially large number of rekeying messages for the set where member actions are very frequent. Based on the idea of separating long and short-duration members, we propose a hybrid rekeying protocol aiming at reducing the rekeying cost of the set of dynamic members. Thanks to this new protocol, the key server can adapt its rekeying scheme regarding to the frequency of membership operations. For each rekeying interval, the key server will first compute and compare the rekeying cost of three different schemes which differ regarding to the data structure defined for the dynamic set and will choose the scheme with the cheapest cost. Thus, the rekeying cost will always be optimized for each rekeying interval.