Optimistic Asynchronous Multi-Party Contract Signing
N. Asokan, Birgit Baum-Waidner, Matthias Schunter, Michael Waidner · 1998
A contract is a non-repudiable agreement on a given contract text, i.e., it can be used to prove unanimous agreement between its signatories to any veri er. A contract signing protocol is used to fairly compute a contract so that, even if n 1 of the n signatories misbehave, either all or none of them obtain a contract. Optimistic contract signing protocols use a third party to ensure fairness, but in such a way that the third party is not actively involved in case all parties are honest. Since no satisfactory protocols without any third party exist, this seems to be the best one can hope for. We present the rst optimistic multi-party contract signing protocol for asynchronous networks. Previous constructions supported synchronous networks only. We show how any such contract signing protocol can be used to construct an optimistic, perfectly fair general function evaluation protocol for dishonest majorities. Previous constructions did not use a third party at all but achieved fairness in a probabilistic sense only.