Resilient LKH: Secure multicast key distribution schemes

Multicasting has become the main mode communication for providing a wide range of Internet services such as video broadcasting and multi-party teleconferencing, where data must be delivered to multiple recipients. The main focus of the work on securing multicast applications has been to control access and to ensure that only authorised users can access the broadcast. The authorised group is not fixed and may change over time and hence efficient methods of re-keying are of very important. Logical Key Hierarchy (LKH) schemes are schemes that use a logical tree to assign keys to users: each user will be attached to a leaf of the tree and will own all the keys allocated to the nodes from that leaf to the root of the tree. In this paper we propose a new LKH scheme in which only a subset of leaves are attached to users. This allows separation of the key sets of the users and providing protection against collusion attack. This property combined with the logarithmic size of the group controller storage makes the approach very attractive. We give a number of constructions, the best of which also has logarithmic cost for users' key storage and communication.