Introduction: Brief Encounters

Abstract

Welcome to the 17th Security Protocols Workshop; the theme this year is “Brief Encounters”.

Traditional authentication protocols were designed to be re-run every time you had an interaction with the system. That’s because, as Roger Needham was fond of saying, the original protocols were designed on the assumptions that message payloads were expensive, and state was evil. By this he meant that the cost of maintaining any significant amount of state, for the duration of time between presentations by the client to the system, was prohibitive for systems with any significant amount of throughput. And the option of bundling the state up and moving it across the network to the client in the way that we do with stateless file-servers was out, because the high costs of message payloads wouldn’t allow you to transfer significant amounts of state in that way.