A Protocol for Signing Contracts Based on Oblivious Transfer

If two parties want to sign a contract C over a communication network, they must “simultaneously” exchange their commitments to C Since simultaneous exchange is usually impossible in practice, protocols are needed to approximate simultaneity by exchange partial commitments in a piece by piece manner The party of secondly sending commitments may have a slight advantage; a “fair” protocol must keep this advantage within acceptable limits The protocol for signing a contract is improved based on the research result of secure multiparty computation In this protocol, the parties obliviously transfer the signed bit and the committed bit; the other parties can prove the validity of this bit based on the confirming sub protocol, but he can’t gain more information about the whole signature by accumulating the signed bit or the committed bit After the parties exchange the whole signed information, they declare the commitment about the signature respectively, and gain the whole signature of the other party At this moment, the party doesn’t care about the advance quit of the other party, because he has gained the whole signed information Finally, it is proved that this protocol is quit fairness