A nonrepudiable bitstring commitment scheme based on a public-key cryptosystem

Commitment schemes are building blocks for guaranteeing fairness in higher-level cryptographic protocols such as mental poker protocols and others. A party Alice commits to a value v (a bit or a bitstring) without revealing it. Alice should not be able to cheat by opening the commitment as v' ≠ v nor to deny having committed at all. Most commitment schemes in the literature rely on hash functions, which should be strongly collision-free for the scheme to be secure. Yet collision-freeness can only be empirically checked and cannot be met with total certainty. We present a commitment scheme which avoids hash functions by using a public-key cryptosystem instead.