Expander Graphs for Digital Stream Authentication and Robust Overlay Networks

We use expander graphs to provide eÆcient new constructions for two security applications: authentication of long digital streams over lossy networks and building scalable, r obust overlay networks.Here is a summary of our contributions: (1) To authenticate long digital streams over lossy networks, we provide a construction with a provable lower bound on the ability to authenticate a packet | and that lower bound is independent of the size of the graph. T o achieve this, we present an authentication expander graph with constant degree. (Previous work, such as [MS01], use d authentication graphs but requir ed graphs with degree line ar in the number of vertic es.) (2) T o build eÆcient, robust, and scalable overlay networks, we provide a construction using undirected expander graphs with a provable lower bound on the ability of a br oadc ast message to successfully reach any receiver. This also gives us a new, more eÆcient solution to the decentralized certi cate r evocation problem [WLM00]. This research was suported in part by the Defense Advanced Researc h Projects Agency under D ARPA contract N6601-99-28913 (under supervision of the Space and Naval Warfare Systems Cen ter San Diego), by the National Science foundation under grant FD99-79852, and by the United States P ostal Service under grant USPS 1025 92-01-Z-0236. Views and conclusions contained in this document are those of the authors and do not necessarily represent the oÆcial opinion or policies, either expressed or implied of the US government or any of its agencies, DARPA, NSF, or USPS. ySome of this w ork was done while the author was on leave at the University of California at Berkeley. Supported in part by a David and Lucile Packard F ellowship for Science and Engineering and NSF Grant CCR-9912428.