Algorithm for updating key forms the basis for any group key management (GKM) system. Existing hierarchical key tree based GKMs are complex, having high computational and communication overhead complexities up to O(logn). In this paper an improved multicast key management (MKM) system is presented, in which only few keys used for encrypting group key are renewed with both backward and forward secrecy being perfectly guaranteed. Furthermore, a mechanism named OWFDL (one-way function and double-lock encryption based) was introduced to reduce the complexities, in which an efficient algorithm of rekeying the group when many members join and leave in a batch interval is proposed. The results show that the OWFDL scheme can reduce both to O(1), which assures perfect multicast secrecy, that is not possible with the previous key management schemes.