Automated analysis of security protocols with global state
This work addresses a gap in automated verification for security protocols with non-monotonic state, which is crucial for systems like key servers and APIs, though it is incremental as it builds on existing formalisms like the applied pi calculus and Tamarin prover.
The authors tackled the problem of automated verification for security protocols with global state, which existing tools often cannot handle, by proposing a process calculus that translates to multiset rewrite rules and implementing a prototype tool; they demonstrated its application on case studies including PKCS#11 and Yubikey.
Security APIs, key servers and protocols that need to keep the status of transactions, require to maintain a global, non-monotonic state, e.g., in the form of a database or register. However, most existing automated verification tools do not support the analysis of such stateful security protocols - sometimes because of fundamental reasons, such as the encoding of the protocol as Horn clauses, which are inherently monotonic. A notable exception is the recent tamarin prover which allows specifying protocols as multiset rewrite (msr) rules, a formalism expressive enough to encode state. As multiset rewriting is a "low-level" specification language with no direct support for concurrent message passing, encoding protocols correctly is a difficult and error-prone process. We propose a process calculus which is a variant of the applied pi calculus with constructs for manipulation of a global state by processes running in parallel. We show that this language can be translated to msr rules whilst preserving all security properties expressible in a dedicated first-order logic for security properties. The translation has been implemented in a prototype tool which uses the tamarin prover as a backend. We apply the tool to several case studies among which a simplified fragment of PKCS\#11, the Yubikey security token, and an optimistic contract signing protocol.