Equivocable and extractable commitment schemes

Abstract

We investigate commitment schemes with special security properties, such as equivocability and extractability, motivated by their applicability to highly secure commitment schemes, such as non-malleable or universally-composable commitment schemes. In the public random string model, we present constructions of non-interactive commitment schemes (namely, both the commitment phase and the decommitment phase consist of a single message sent from committer to receiver) that are both equivocable and extractable. One of our constructions uses necessary and sufficient assumptions (thus improving over previous constructions). We combine these constructions with the non-malleability construction paradigm of [8] and obtain, in the public random string model, a non-interactive commitment scheme that is non-malleable with respect to commitment. The assumptions used for this scheme are more general than those used in previous constructions. © Springer-Verlag Berlin Heidelberg 2003.