One feature provides a method for a client node to establish a session key with a group node by obtaining an epoch identity value associated with a current epoch, wherein obtaining the epoch identity value includes one of computing the epoch identity value based on a node real time or negotiating the epoch identity value with the group node, computing a restricted key using a shared secret key, the epoch identity value, and a group node identity associated with the group node, and executing a session key establishment protocol with the group node to derive the session key using the restricted key as a master key in the session key establishment protocol. The session key may be established between the group node and the client node even though communications between the group node and the central node is only intermittently available during the current epoch.