A Calculus for Game-Based Security Proofs

The game-based approach to security proofs in cryptography is a widely-used methodology for writing proofs rigorously. However a unifying language for writing games is still missing. In this paper we show how CSLR, a probabilistic lambda-calculus with a type system that guarantees that computations are probabilistic polynomial time, can be equipped with a notion of game indistinguishability. This allows us to define cryptographic constructions, effective adversaries, security notions, computational assumptions, game transformations, and game-based security proofs in the unified framework provided by CSLR. Our code for cryptographic constructions is close to implementation in the sense that we do not assume arbitrary uniform distributions but use a realistic algorithm to approximate them. We illustrate our calculus on cryptographic constructions for public-key encryption and pseudorandom bit generation.