Optimising group key management for frequent-membership-change environment in VANET

In this paper, we propose a tree-based optimal group key management algorithm using a batch rekeying technique, which changes a set of keys at a certain time interval. In batch rekeying, the server collects all the joining and leaving requests during the time interval, and generates rekeying messages. In the proposed algorithm, when a vehicle joins a group, it is located at a certain leaf node of the key-tree according to its leaving time. This reduces the size of the rekeying messages because the vehicles that leave during the same time interval are concentrated on the same parent node. With the proposed scheme, tree-based group key management can be employed to the VANET because it solves the communication overhead problem. Using simulations, we demonstrate that our scheme remarkably reduces the communication cost for updating the group key.