Stateful Subset Cover

This paper describes a method to convert stateless key revocation schemes based on the subset cover principle into stateful schemes. The main motivation is to reduce the bandwidth overhead to make broadcast encryption schemes more practical in network environments with limited bandwidth resources, such as cellular networks. This modification is not fully collusion-resistant. A concrete new scheme based on the Subset Difference scheme [1] is presented, accomplishing a bandwidth overhead of Δm + 2 Δr + 1 compared to e.g. Logical Key Hierarchy’s 2(Δm + Δr)logm, where Δm and Δr is the number of members added and removed since the last stateful update and m is the number of current members.