In this thesis, we propose and analyze a multicast key backbone for secure group communications. We also utilize the correlated relationships between the mobile users in the wireless communications networks. When a batch member joins or leaves the group communications, the system has to update and distribute encryption keys to assure that only active members could receive the latest information. In previous tree-based multicast key management schemes, the depth of the key tree is unbounded and analytically deriving the exact value of the corresponding average update cost remains an open problem. And in previous schemes, the different mobile user arrives in and leaves from the system at different time. In contrast, the depth of the proposed multicast key backbone is fixed and the arriving or leaving users are more than one. We utilize these two characteristics and simulate the system to get the average update cost per time unit. We can find that this scheme can improve the efficiency of the system in some special cases when updating the new key.