A secure re-keying scheme with key recovery property

A commonly used solution for controlling access to information in a multicast group is to encrypt the data using a group key (session key). The group key is only known by users in the group, but not others. A multicast group is dynamic in the sense that group memberships changes in each session. To start a new session, the session key must be updated through a re-keying scheme. In this paper we propose a re-keying scheme for multiple user revocation and multiple user join. Our construction employs logical key hierarchy in conjunction with oneway hash chain to achieve higher efficiency. We prove that our scheme satisfies forward secrecy, backward secrecy and forward-backward secrecy. We also provide key recovery property which gives a system the ability to recover a session key using the previous and future session keys. We show security of the system.