Verified Correctness and Security of mbedTLS HMAC-DRBG
This provides verified correctness and security guarantees for a widely-used cryptographic random number generator implementation, addressing critical security concerns for systems relying on mbedTLS.
The authors formalized the HMAC-DRBG specification from NIST 800-90A and proved its cryptographic security (pseudorandom output) using hybrid game-based proofs, then verified that the mbedTLS C implementation correctly follows this specification, with all proofs machine-checked in Coq.
We have formalized the functional specification of HMAC-DRBG (NIST 800-90A), and we have proved its cryptographic security--that its output is pseudorandom--using a hybrid game-based proof. We have also proved that the mbedTLS implementation (C program) correctly implements this functional specification. That proof composes with an existing C compiler correctness proof to guarantee, end-to-end, that the machine language program gives strong pseudorandomness. All proofs (hybrid games, C program verification, compiler, and their composition) are machine-checked in the Coq proof assistant. Our proofs are modular: the hybrid game proof holds on any implementation of HMAC-DRBG that satisfies our functional specification. Therefore, our functional specification can serve as a high-assurance reference.