An Optimal Certificate Dispersal Algorithm for Mobile Ad Hoc Networks

摘要

In this paper, we focus on the problem that in an ad hoc network, how to send a message securely between two users using the certificate dispersal system. In this system, special data called certificate is issued between two users and these issued certificates are stored among the network. Our final purpose on this certificate dispersal problem is to construct certificate graphs with lower dispersability cost which indicates the average number of certificates stored in each node in an ad hoc network. As our first step, when a certificate graph is given, we construct two efficient certificate dispersal algorithms for strongly connected graphs and directed graphs in this paper. We can show that for a strongly connected graph G = (V, E) and a directed graph H = (V′,E′), new upper bounds on dispersability cost on the average number of certificates stored in one node are O(D_G + E/V) and O(p_Gd_(max) + E′/V′) respectively, where D_G is the diameter of G, d_(max) is the maximum diameter of strongly connected components of H and p_G is the number of strongly connected components of H. Furthermore, we give some new lower bounds for the problem and we also show that our algorithms are optimal for several graph classes.