The use of logic in the analysis of cryptographic protocols

Logics for cryptographic protocol analysis are presented, and a study is made of the protocol features that they are appropriate for analyzing: some are appropriate for analyzing trust, others security. It is shown that both features can be adequately captured by a single properly designed logic. The goals and capabilities of M. Burrows, M. Abadi and R. Needham's (1989) BAN logic are examined. It is found that there is confusion about these. While the logic is extremely useful heuristically, as a formal method it is seen to be ultimately unacceptable. Formal semantics is explored as a reasoning tool and the importance of soundness and completeness for protocol security is discussed. The KPL logic is used to resolve a debate over an alleged flaw in BAN logic and is shown to be uniquely capable of dealing with certain protocol security issues.<>