Verified Correctness and Security of OpenSSL HMAC

We have proved, with machine-checked proofs in Coq, that an OpenSSL implementation of HMAC with SHA256 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 compilercorrectness 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.