Séminaire de Cryptographie

Accueil     Présentation     Archives

Marion Daubrignard

Towards Automatic Verification of Security Proofs forCryptographic Primitives

Providing security proofs instead of arguing lack of existing relevant attacks is a quite new approach when it comes to cryptography. In the last thirty years, a lot of work has been done to formalize security of systems and prove of the achievement of security criteria. It has resulted in the design of a great number of proofs under various hypotheses. Though a step in the right direction, these pencil-and-paper proofs are so numerous, involved and technical that the community has difficulty to carefully check them. The well-known example of the encryption scheme OAEP whose security proof, apparently correct, was corrected seven years after its publication illustrates that security-dedicated verification tools need to be designed.

Our work takes place in the so-called computational model, where messages are considered to be bitstrings, and system adversaries are probabilistic Turing machines. A proof of security is then a complexity-theoretic reduction argument: the probability of success of an adversary in solving a security challenge is reduced to its ability to solve a known difficult problem (given a fixed amount of resources).  Firstly, we provide some intuition on usual security requirements, and common sketches of security proofs. Then, we present a semantics and a logic to formalize security proofs. One could say there are several levels in automatic proving: computer-aided verification of proofs, computer-aided design of proofs, and automatic generation of proofs. We show how our inference rules can be used to derive proofs and verify them automatically, or sometimes perform a proof search using some additional inputs.