@TechReport{YL00-bound,
  author =	 {Yang Richard Yang and Simon S. Lam},
  title =	 {A Secure Group Key Management Communication Lower
                  Bound},
  institution =	 {Department of Computer Sciences, The University of
                  Texas at Austin},
  year =	 2000,
  number =	 {TR-00-24},
  address =	 {Austin, TX},
  month =	 {September},
  abstract =	 {We discuss in this paper a lower bound on
                  communication cost for secure group key management
                  protocols. To model a rekeying process, we introduce
                  the concept of rekey encryption graphs. Using the
                  rekey encryption graphs, we show that given the
                  forward access control requirement, i.e. a user who
                  has left the secure group cannot have access to
                  future group keys, there exists a sequence of 2n
                  user join and leave requests such that the amortized
                  per request communication cost is ln(n). Given the
                  known protocols that have achieved this lower bound,
                  in order to further improve the scalability of group
                  rekeying communication protocol performance, future
                  research needs to either allow more types of
                  operations or to relax security requirements to
                  achieve better performance.}
}