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.

This paper describes various possible attacks on temporal properties such as temporal records of payment times and declarations of the closing times for electronic submissions, and explains defense measures that use a trusted third party to provide temporal accountability. We propose a secure electronic submission protocol as a typical time-sensitive application and a temporal accountability logic, which is an extension of Kailar’s work. We analyze the proposed protocol by applying our temporal accountability logic, and describe some modifications of the protocol, which reduce the total number of flows while keeping the protocol as logically secure as the original one in terms of temporal accountability. 1