基于区块链的高效公平多方合同签署协议

With the wide application of digital currency, blockchain as its core support has quickly become the focus of attention. Since the blockchain can act as a decentralized trusted third party (TTP), it is introduced to ensure fairness in the design of contract signing protocols. However, most of the existing protocols only apply to contract signing between two parties. When they are extended to multi-party contract signing protocols, the participants' workload becomes enormous because every signature needs to be verified. Therefore, designing a simple and efficient multi-party fair contract signing protocol is a key issue for e-commerce. The verifiably encrypted signature (VES) can effectively guarantee the fairness of the transaction process on the Internet and can be naturally used to design contract signing protocols. Aggregate signature can aggregate multiple signatures into one signature, thereby improving the efficiency of verification. Based on certificateless aggregate signature scheme and verifiably signature scheme, this paper proposes a certificateless aggregate verifiably signature scheme (CLAVES). We present a concrete construction of the scheme, and prove its security. Then we use this scheme to design a multi-party fair contract signing protocol based on blockchain. The proposed protocol is divided into two phases. (1) In the off-blockchain phase, the signing party executes the CLAVES scheme and generates their respective CLAVES signatures. If the verification of CLAVES signatures is valid, then protocol enters the on-blockchain phase. Otherwise, the protocol is terminated. (2) In the on-blockchain phase, using the penalty-based fair exchange protocol (claim or refund, COR), the signatories exchange their secret values fairly on the blockchain, and finally, they can extract the ordinary signatures by some computation. Thereby completing the signing of the contract. Through analysis and comparison with the existing multi-party contract signing protocols, the multi-party contract signing protocol proposed in this paper is efficient and fair.