A group-key agreement protocol secure against the malleability attacks

In group key agreement protocols, it is important to consider the effects of existence of malicious insiders. In this paper, we define a type of key-control attacks and the security against them for group key agreement protocols with malicious insiders. Then, we give a first ideal functionality of group key agreement that takes key-control attacks (as well as key-integrity attacks) into consideration, and construct a group key agreement protocol that securely realizes the ideal functionality. The construction is efficient enough for practical uses, being comprised of 2 rounds and n messages for n-party groups.