Communication Complexity of Group Key

LIMITED DISTRIBUTION NOTICE This report has been submitted for publication outside of IBM and will probably be copyrighted if accepted for publication. It has been issued as a Research Report for early dissemination of its contents. In view of the transfer of copyright to the outside publisher, its distribution outside of IBM prior to publication should be limited to peer communications and speciic requests. After outside publication, requests should be lled only by reprints or legally obtained copies of the article (e.g., payment of royalties). Abstract Communication complexity has always been an important issue when designing group key distribution systems. This paper systematically studies what can be achieved for the most common measures of protocol complexity. Lower bounds for the total number of messages, the total number of exchanges, and the number of necessary rounds are established, whereby models that allow broadcasting have to be distinguished from those that do not. For every measure of protocol complexity, we furthermore show that the corresponding bound is realistic for Diie{Hellman-based protocols by referring to or introducing protocols that match the bound or exceed it by only one.