Distributing Key Updates in Secure Dynamic Groups

We focus on the problem of distributing key updates in secure dynamic groups. Due to changes in group membership, the group controller needs to change and distribute the keys used for ensuring encryption. However, in the current key management algorithms the group controller broadcasts these key updates even if only a subset of users need them. In this paper, we describe a key distribution algorithm for distributing keys to only those users who need them. Towards this end, we propose a descendent tracking scheme. Using our scheme, a node forwards an encrypted key update only if it believes that there are descendents who know the encrypting key. We also describe an identifier assignment algorithm which assigns closer logical identifiers to users who are physically close in the multicast tree. We show that our identifier assignment algorithm further improves the performance of our key distribution algorithm as well as that of a previous solution. Our simulation results show that a bandwidth reduction of upto 55% is achieved by our algorithms.