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Towards Extensional Goals in Authentication Protocols

Colin Boyd
Information Security Research Centre
School of Data Communications
Queensland University of Technology
Brisbane Q4001


The importance of clarifying the goals of a cryptographic protocol is widely recognised. The majority of authors have addressed intensional goals which are concerned with correct operation within the protocol itself. Extensional goals are properties independent of the protocol and define what the protocol is designed to achieve. This paper reviews the previous literature on goals in protocols and classifies them as intensional or extensional goals. A hierarchy of extensional protocol goals is proposed which includes the major proposed goals for key establishment. It is shown how these extensional goals can be exploited to motivate design of entity authentication protocols.