Verified correctness and security of OpenSSL HMAC

Abstract

We have proved, with machine-checked proofs in Coq, that an OpenSSL implementation of HMAC with SHA- 256 correctly implements its FIPS functional specification and that its functional specification guarantees the expected cryptographic properties. This is the first machine-checked cryptographic proof that combines a source-program implementation proof, a compiler-correctness proof, and a cryptographic-security proof, with no gaps at the specification interfaces. The verification was done using three systems within the Coq proof assistant: the Foundational Cryptography Framework, to verify crypto properties of functional specs; the Verified Software Toolchain, to verify C programs w.r.t. functional specs; and CompCert, for verified compilation of C to assembly language.