  In the secure group communication, data is transmitted in such a way that
only the group members are able to receive the messages. The main problem in
the solution using symmetric key is heavy re-keying cost. To reduce re-keying
cost tree based architecture is used. But it requires extra overhead to balance
the key- tree in order to achieve logarithmic re-keying cost. The main
challenging issue in dynamic and secure multimedia multicast communication is
to design a centralized group key management scheme with minimal computational,
communicational and storages complexities without breaching security issues.
Several authors have proposed different centralized group key management
schemes, wherein one of them proposes reducing communicational complexity but
increases computational and storage costs however another proposes decreasing
the computational and storage costs which eventually breaches forward and
backward secrecy. In this paper we propose a comparatively more efficient
centralized group key management scheme that not only minimize the
computational, communicational and storages complexities but also maintaining
the security at the optimal level. The message encryptions and decryptions
costs are also minimized. Further, we also provide an extended multicast
scheme, in which the several requests towards leaving or joining the group can
be done by large number of members simultaneously. In order to obtain better
performance of multicast encryption, the symmetric-key and asymmetric-key
cryptosystems may be combined.
