We present the Open Verifier approach for verifying untrusted code using customized verifiers. This approach can be viewed as an instance of foundational proof-carrying code where an untrusted program can be checked using the verifier most natural for it instead of using a single generic type system. In this paper we focus on a specialized architecture designed to reduce the burden of expressing both type-based and Hoare-style verifiers.
A new verifier is created by providing an untrusted executable extension module, which can incorporate directly pre-existing non-foundational verifiers based on dataflow analysis or type checking. The extensions control virtually all aspects of the verification by carrying on a dialogue with the Open Verifier using a language designed both to correspond closely to common verification actions and to carry simple adequacy proofs for those actions.
We prove the soundness of the framework, and we describe our experience implementing proof-carrying code, typed assembly language, and dataflow or abstract interpretation based verifiers in this unified setting.