Abstract. The proliferation of group-centric computing and communication motivates the need for mechanisms to provide group access control. Group access control includes mechanisms for admission as well as revocation/eviction of group members. Particularly in ad hoc groups, such as peer-to-peer (P2P) systems and mobile ad hoc networks (MANETs), secure group admission is needed to bootstrap other group security services. In addition, secure membership revocation is required to evict misbehaving or malicious members. Unlike centralized (e.g., multicast) groups, ad hoc groups operate in a decentralized manner and accommodate dynamic membership which make access control both interesting and challenging. Although some recent work made initial progress as far as the admission problem, the membership revocation problem has not been addressed. In this paper, we develop an identity-based group admission control technique which avoids certain drawbacks of previous (certificate-based) approaches....