Big progress in verification

Formal verification is not easy task, for example ComCert compiler is able to verify, that optimizations haven't modified semantic of a program. Paper Verified correctness and security of OpenSSL HMAC describes verification of the whole "stack":

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.