Abstract:

A fair contract signing protocol allows two potentially mistrusted parties to exchange their digital signatures over the Internet in a fair way, so that after the execution of the protocol, either each of them can get the effective signature of the other’s signature or neither party does. Most of the traditional fair electronic contract signing protocols introduce the trusted third party, and these protocols rely on the reliability of third parties to ensure the fairness, however one of the shortcomings of this type of protocol is that if the third party is dishonest and collusion with one of the parties concerned with the protocol, it will be unfair to the other party. In order to reduce the reliance on trusted third parties, this paper designs a new fair electronic contract signing protocol by using the convertible non-repudiation signature algorithm and the public verifiable secret sharing principle. The protocol not only satisfies the property of abuse-freeness, but also reduces the requirement of trustworthiness to the offline third party by introducing the distributed semi-trusted third party, which makes the contract signing protocol have better fairness.

Key words: contract signing, convertible, undeniable signature, publicly verifiable secret sharing