One Picture is Worth a Dozen Connectives: A Fault-Tree Representation of NPATRL Security Requirements

In this paper we show how we can increase the ease of reading and writing security requirements for cryptographic protocols at the Dolev-Yao level of abstraction by developing a visual language based on fault trees. We develop such a semantics for a subset of NPATRL, a temporal language used for expressing safety requirements for cryptographic protocols, and show that the subset is sound and complete with respect to the semantics. We also show how the fault trees can be used to improve the presentation of some specifications that we developed in our analysis of the Group Domain of Interpretation (GDOI) protocol. Other examples involve a property of Kerberos 5, and a visual account of the requirements in Lowe’s authentication hierarchy.