Author : N Vasavi Reddy 1
Date of Publication :7th March 2016
Abstract: Key agreement is a mechanism that allows two or more parties to securely share a secret key (called a session key). Starting from Diffie-Hellman for the two-party case. However, almost all the protocols assume a complete connectivity graph: any two users can communicate directly. In the real world, this is not always true. For instance, in social networks such as Face book, Skype, Wechat and Google+, a user is only connected with his friends. For a group of users (e.g., the faculty union in a university) who wish to establish a session key, it is not necessary that any two of them are friends. But they might still be connected indirectly through the friend network. Of course, we can still regard them as directly connected by regarding the intermediate users as routers. However, this is quite different from a direct connection. First, indirectly connected users may not have the public information of each other (e.g., public-key certificate). Second, indirectly connected users may not know the existence of each other (e.g., in our faculty union example, one professor in one department may not know another professor in a different department). Third, a message between two indirectly connected users travels a longer time than that between directly connected users. We study the group key agreement with an arbitrary connectivity graph, where each user is only aware of his neighbors and has no information about the existence of other users. Further, he has no information about the network topology. Under this setting, a user does not need to trust a user who is not his neighbor. Thus, if one is initialized using PKI, then he need not trust or remember public-keys of users beyond his neighbors.
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