Verification of a Signature Architecture with HOL-Z

We report on a case study in using HOL-Z, an embedding of Z in higher-order logic, to specify and verify a security architecture for administering digital signatures. We have used HOL-Z to formalize and combine both data-oriented and process-oriented architectural views. Afterwards, we formalized temporal requirements in Z and carried out verification in higher-order logic. The same architecture has been previously verified using the SPIN model checker. Based on this, we provide a detailed comparison of these two different approaches to formalization (infinite state with rich data types versus finite state) and verification (theorem proving versus model checking). Contrary to common belief, our case study suggests that Z is well suited for temporal reasoning about process models with rich data. Moreover, our comparison highlights the advantages of this approach and provides evidence that, in the hands of experienced users, theorem proving is neither substantially more time-consuming nor more complex than model checking.