Applying Formal Methods . . . Device: An Experience Report

SCR (Software Cost Reduction) is a formal method for specifying and analyzing system requirements that has previously been applied to control systems. This paper describes a case study in which the SCR method was used to specify and analyze a different class of system, a cryptographic system called CD, which must satisfy a large set of security properties. The paper describes how a suite of tools supporting SCR -- a consistency checker, simulator, model checker, invariant generator, theorem prover, and validity checker -- were used to detect errors in the SCR specification of CD and to verify that the specification satis es seven security properties. The paper also describes issues of concern to software developers about formal methods -- e.g., ease of use, cost-effectiveness, scalability, how to translate a prose specification into a formal notation, and what process to follow in applying a formal method -- and discusses these issues based on our experience with CD. Also described are some unexpected results of our case study