CAGE: Clique-based Assignment of Group kEy

Due to the unique operational environment of WSNs combined with their communication medium that is open to eavesdroppers, the traditional wireless network threats manifest in new forms. Consequently, key management protocols have become paramount in mitigating the damage caused. Numerous group-key protocols have been proposed in an effort to restrict access to only legitimate users. However, the group-key assignment protocols in literature neither address the issue of the size of a group nor its geographic boundaries. Consequently, in applications like watchdog-based reputation monitoring systems, malicious users are encouraged to pollute the reputation values by bad-mouthing benign nodes. On the otherhand, pairwisekey protocols are very restrictive and impose substantial storage overhead on resource constrained sensors. They do not suit the reputation monitoring systems either, since messages encrypted with pairwise keys cannot be monitored by watchdogs. In this paper, we propose CAGE, a novel, distributed, clique-based group-key assignment protocol, which distinctly addresses the size and geographic restrictions on groups. Our protocol is a simple distributed method, yet effective in securing the neighborhood communication. We prove that CAGE is an optimal solution through simulations and analysis.