We present a new access control mechanism for P2P networks
with distributed enforcement, called P2P Access Control System (PACS). PACS enforces powerful access control models like RBAC with administrative delegation inside a P2P network in a pure P2P manner, which is not possible in any of the currently used P2P access control mechanisms. PACS uses client-side enforcement to support the replication of confidential data. To avoid a single point of failure at the time of privilege enforcement, we use threshold cryptography to distribute the enforcement among the participants. Our analysis of the expected number of messages and the computational effort needed in PACS shows that its increased flexibility comes with an acceptable additional overhead.