A contract is a non-repudiable agreement on a given contract text, i.e., a contract can be used to prove agreement between its signatories to any verifier. A contact signing protocol is used to fairly compute a contact so that, even if n-1 of the n signatories misbehave, either all or none of the 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 an optimistic multi-party contract signing protocol for synchronous networks. The construction is significantly more efficient than the only known asynchronous multi-party contract signing protocol, and only 2-3 times more expensive than the trivial solution using an inline third party.
We show how to use multi-party contract signing to efficiently solve other atomicity problems securely, in particular optimistic certified mail and optimistic fair exchange of signatures. We also outline a generic construction for optimistic multi-party fair exchange.
By: N. Asokan, B. Baum-Waidner, M. Schunter, M. Waidner
Published in: RZ3089 in 1999
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