Developments in the area of group communication have been enormous. Multicasting is the group communication paradigm of future, as it saves bandwidth considerably. The main features that makes multicasting as an attractive one, also makes security and the related tasks still a subject of research. Membership in a multicast group is highly dynamic, with receivers entering and leaving the multicast session without explicit knowledge of other hosts. This study concentrates on secure data transmission among highly dynamic multicast groups. In dynamic groups, key management is a complicated procedure since users join and leave at any time. In the proposed architecture to reduce the number of key updates whenever the member joins or leaves, intermediate node in the tree maintains two keys. One is to commune with its parent node and another is to its children. The results show the performance of this architecture outstrips the existing one in the aspects of rekeying overhead.