In order to ensure secure communication between communicating entities, a secret session key needs to be shared between these entities. This avoids any adversary from intruding and hijacking the communication. An authenticated group key agreement protocol is generally designed to accommodate the need of a group of specific entities in communicating over an open network with a shared secret key, which is used to preserve data confidentiality and integrity. A fault-tolerant group key agreement protocol establishes a shared key among participants of a group even when some malicious participants disrupt key agreement processes. Most of the existing group key agreement protocols operate only when all participants are honest, but do not work when some participants are malicious and attempt to destruct the key agreement processes. In 2013, Anmin Fu, Gongxuan Zhang and Zhenchao Zhu proposed a secure and efficient fault-tolerant group key agreement protocol, which is resistant to different key attack and the message tampering attack according to the security analysis. In this paper, we have proposed an improved version of this protocol which proves to be more efficient in terms of computational cost.

Key agreement is a procedure of creating a secure environment between communicating parties. Sharing a secret key will avoid an adversary from intruding the communication as this key will be known only to the participating entities. A key agreement protocol is said to be authenticated if the protocol is able to ensure that the session key is known only to the intended entities in a protocol run. The first key agreement scheme between two entities was developed by Diffie and Hellman (1976). But this Diffie- Hellman protocol suffers from the man-in-the-middle attack because there is no mutual authentication between the communicating entities. For secure communication between a group of people, a common secret key known only to the members in the group needs to be established so that messages can be encrypted using the secret key and passed among them without intervention from an outsider. The process of establishing a common secret key known only to the members in a group is called group key management. The goal of group key management is to set up and maintain a shared secret key among the group members.

Information Technology Journal, Fault-tolerant, Group key agreement, Different key attack, Message tampering attack, Fault-Tolerant, Key Agreement Protocol .