Sender Key Storage Reduction of Secure Multicast Key Management Schemes Using One-Way Function Tree

Developing scalable infrastructure services for secure multicast communications has been an active research area [1]-[10]. One-way function tree (OFT) [1, 6] is a secure multicast key distribution scheme with logarithmic key update communication overhead in group size N. The OFT scheme has been proposed as a candidate for secure multicast over Internet to the IETF under Multicast Security (MSEC) working group. Though it exhibits good scal-ability in key update communication, it requires O(N) cryptographic keys to be stored by the group owner/center (GC). This paper addresses the problem of designing an OFT with minimal GC storage while maintaining the same key update communication growth rate. In order to improve the storage performance, we formulate the problem of GC storage minimization as a constraint optimization problem. By solving this problem, we show that the center storage can be made to grow slower than linear in group size. We also present an explicit design algorithm for storage performance optimized OFT with a given amount of key update communication overhead