Securing Group Communication in Partially Distributed Systems

Abstract

This paper deals with symmetric key exchange in partially distributed systems. Unlike the traditional distributed approaches for key exchange utilized when we have a centralized KDC (Key Distribution Center), which is a trusted server responsible for key exchange between the users involved in group communication or a KDC for each node, we divide the group of nodes in regions with each having its own KDC. Each user can communicate securely with members of its own region as well as with those belonging to other regions. We use a hierarchical approach to represent the partial distributed structure of the distributed system using key graphs. The outcome is a secure group communication providing authenticity, confidentiality and integrity of messages delivered between groups. Each secure group is represented in form of a triplet (U, N, R) where U is the set of users, N is the set of keys held by the users and R represents a relation on U and R. This approach has been developed keeping in view the scalability issues of the distributed systems where number of group members may increase or decrease with time. For the same reason we use rekeying strategies to redistribute the keys every time a user joins or leaves the group. This approach is irrespective of frequency of joins and leaves. Keywords - Group communication, multicast, partially distributed systems, rekeying, security