Hierarchical CRGK for a Large-scale User Group

The purpose of the group key management is to provide a secure key sharing scheme among the users in a group on a broadcast or a multicast environment. CRGK[1] is the centralized group key management scheme based on the Chinese Remainder Theorem(CRT). It optimizes the number of rekey message, user-side key computation, and number of key storage. However, CRGK is suited for a small size user group because of the computation complexity of the Chinese remainder theorem. In this paper, we propose a hierarchical CRGK scheme which is able to support a large-scale user group. Our approach is to adopt an n-ary tree with the CRGK. Our scheme requires the small number of re-key messages and the short computation time even though the size of a user group increases largely.