A tool for automating the computationally complete symbolic attacker (Extended Abstract)

The design of automated security proofs is a topic extensively studied for over 20 years. One problem that was raised about 12 years ago is the validity (or the scope) of such proofs. Symbolic models are quite far from the implementation. In contrast, modern cryptography typically considers more powerful attackers. This includes of course some computations that are not explicitly specified. This issue has been first addressed by M. Abadi and P. Rogaway [1], followed by many authors. The idea is to prove that the symbolic formal model is sound with respect to the more concrete computational model: if there is no attack in the symbolic model, then there is no attack in the computational model. There are several such soundness proofs, for various primitives and in various contexts (see e.g. [10], [2], [9] to cite only a few). However, all these results require heavy proofs and assume strong hypotheses, some of which are not quite realistic. Typical examples of unrealistic assumptions include: a key cycle is never created, or the attacker does use the key generation algorithm to build his own keys.