Chameleon-Based Optimistic Fair Exchange Protocol

A fair exchange protocol allows two parties to exchange items in a fair way so that either each party gets the other´s item or neither party does. In this paper, we propose a key-exposure-free chameleon hashing scheme based on the discrete logarithm assumption, and prove that it enjoys all advantages of previous schemes: collision resistant, semantic security, message hiding and key exposure freeness. Using this new scheme as kernel, an efficient and secure chameleon-based optimistic fair exchange protocol is proposed. Unlike the vast majority of previously proposed protocols, above approach has no use for verifiably encrypted signature and does not use any zero knowledge proofs, which avoids most of the costly computations. The security of the newly devised protocol is also examined. It is showed that the proposed scheme is secure and efficient.