EPREKM: ElGamal proxy re‐encryption‐based key management scheme with constant rekeying cost and linear public bulletin size

Summary A vast body of literature is filled with many key management schemes constructed using different cryptographic primitives. They aim toward either security goals or improvement in performance efficiency. However, the key management schemes based on proxy re‐encryption suffer from massive communication and computational costs. We propose an ElGamal proxy re‐encryption‐based construction for the key management scheme to resolve this. The proposed scheme involves constant computational and communication costs in rekeying operations and linear public bulletin size. We achieve essential security requirements of forward and backward secrecy in this scheme. The scheme is also secure against the collusion attack. In addition, we address the importance of adequately managing missed rekeying updates for offline users. The existing schemes trivially keep track of each rekeying message on the public bulletin board, which increases the size of the public bulletin with every join/leave operation. However, the proposed scheme uses the public bulletin board so that the handling of offline users is built into the scheme itself, which manages it efficiently. Also, the public bulletin size in the proposed scheme is not dependent on the number of rekeying operations but linear in the number of users.