Towards a Formal Treatment of Secrecy against Computational Adversaries

Polynomial time adversaries based on a computational view of cryptography have additional capabilities that the classical Dolev-Yao adversary model does not include. To relate these two different models of cryptography, in this paper we enrich a formal model for cryptographic expressions, originally based on the Dolev-Yao assumptions, with computational aspects based on notions of probability and computational power. The obtained result is that if the cryptosystem is robust enough, then the two adversary models turn out to be equivalent. As an application of our approach, we show how to determine a secrecy property against the computational adversary