Group key management with efficient rekey mechanism: A Semi-Stateful approach for out-of-Synchronized members

Our KeyDer-GKM scheme is very efficient since it can be implemented by using hash and XOR functions only. Our ReEnc-GKM scheme allows a member to reduce the cost of computing the up-to-date group key to one decryption by outsourcing log N operations. Both of our schemes are shown immune to the collusion attacks. For KeyDer-GKM, a set of collusive members cannot recover an unauthorized group key. For ReEnc-GKM, a set of collusive members cannot distinguish an unauthorized group key from a random string.