An Efficient Group Key Management Using Code for Key Calculation for   Simultaneous Join/Leave: CKCS
  This paper presents an efficient group key management protocol, CKCS (Code for Key Calculation in Simultaneous join/leave) for simultaneous join/leave in secure multicast. This protocol is based on logical key hierarchy. In this protocol, when new members join the group simultaneously, server sends only the group key for those new members. Then, current members and new members calculate the necessary keys by node codes and one-way hash function. A node code is a random number which is assigned to each key to help users calculate the necessary keys. Again, at leave, the server just sends the new group key to remaining members. The results show that CKCS reduces computational and communication overhead, and also message size in simultaneous join/leave. 
Melisa Hajyvahabzadeh, Elina Eidkhani, S. Anahita Mortazavi, Alireza   Nemaney Pour
cs.CR