A Fair Three-Party Contract Singing Protocol Based on Blockchain

Contract signing allows two or more mutual distrust entities to sign a predefined digital contract in a fair and effective way. It is a significant cryptographic service in commercial environment, where the crucial property for contract signing protocols is fairness. The existing solutions involved a trusted third party (TTP) to solve the problem of fairness. However, the existence of TTP become a bottleneck, since it can be a single point of failure or suffer from external or internal attack. In this paper, we propose a fair three-party contract singing protocol based on the primitive of blockchain, which provides a novel solution to design a fair protocol without a TTP. Our proposed construction makes use of the verifiable encrypted signature and the blockchain to accomplish the fair exchange. As result, a dishonest party will be monetarily penalized as it aborts after receiving the current output. Moreover, the privacy of the contract content can be preserved on the public chain.