【作者】 王焱；

【导师】 黎琳；

【作者基本信息】 北京交通大学 ， 计算机技术（专业学位）， 2022， 硕士

【摘要】 电子合同的签署是数字化办公中一项重要的密码服务。传统的电子合同签署协议引入中心化的第三方来保证合同签署的公平性,但在实际应用中无法保证与第三方数据传输的安全性,从而威胁签署方的隐私安全,而且如果不诚实的第三方与某一签署方合谋,将打破合同签署的公平性,造成其他签署方的经济损失。因此,提供服务的第三方必须是可靠的,以保证合同签署协议的公平性和隐私性。区块链技术作为数字货币的基础技术,将其作为去中心化的可信第三方,避免了传统的中心化的第三方问题。然而,区块链的公开访问的特性给签署方的隐私保护带来新的挑战。此外,现有的基于区块链的公平合同签署协议大多是服务于两方的,因此设计多方的隐私保护公平合同签署协议势在必行。本文对基于区块链和可验证加密签名的多方隐私保护公平合同签署协议进行研究,主要工作如下:(1)基于Hashimoto和Ogata的无证书聚合签名方案,提出了一个高效的基于双线性对的无证书聚合可验证加密签名方案(Certificateless Aggregate Verifiably Encrypted Signature,CLA-VES)。首先给出方案的形式化定义和安全模型;然后在随机预言模型下将其安全性归约到计算Diffie-Hellman困难问题,方案满足正确性、机密性、不可伪造性、不可否认性、不透明性和公开验证性;最后通过与现有方案的性能对比分析和实验分析,论证了方案的可行性和高效性。CLA-VES方案结合了无证书签名和聚合签名的优点,将可验证加密签名聚合为一个固定大小的聚合签名,解决了密钥恢复和证书管理问题,降低了网络通信量和计算量,与同类方案相比具有较高的验证效率。(2)在CLA-VES方案的基础上设计了基于区块链的多方隐私保护公平合同签署协议(Multi-party Privacy-preserving Fair Contract Signing Protocol,MP~2FCSP),协议满足公平性、隐私性、不可篡改性、时效性和不可否认性。MP~2FCSP协议使用以太坊智能合约实现离线的可信第三方功能,达到去中心化和保证协议公平性的目的;签署方共同协商出盲化因子,盲化签名并加密合同内容,可以解决在合同签署过程中的隐私保护问题;使用以太坊模拟协议的真实应用场景,对以太币的成本进行分析,论证了协议的可行性。更多还原

【Abstract】 Electronic contract signing is an essential cryptographic service in the digital office.Traditional electronic contract signing protocols introduce a centralized third party to ensure the fairness of the contract signing process.However,in practice,the security of data transmission with the third party cannot be guaranteed,which threatens the signatory’s privacy.If a dishonest third party conspires with a signatory,the contract signing process will become unfair,causing financial damages.Therefore,the third-party service provider must be trustworthy to ensure the fairness and privacy of the contract signing process.Blockchain technology,the foundation of digital currency,is deployed as a trusted third party decentralized to avoid the traditional centralized third-party problem.However,the publicly accessible character of blockchain introduces new challenges to the privacy of signatories.In addition,most of the existing blockchain-based fair contract signing protocols serve two parties,so it is imperative to design a multi-party privacy-protecting fair contract signing protocol on the blockchain.This paper investigates the multi-party privacy-preserving fair contract signing protocol based on the blockchain and verifiably encrypted signatures.The main contributions are as follows:(1)An efficient bilinear pair-based certificateless aggregate verifiably encrypted signature(CLA-VES)scheme is proposed based on Hashimoto and Ogata’s certificateless aggregated signatures scheme.First,we propose the definition and security model of the CLA-VES scheme.Besides,the correctness,confidentiality,unforgeability,non-repudiation,opaqueness,and verifiability of our scheme are reduced to solve the Computational Diffie-Hellman problem in the random oracles model.Finally,the feasibility and efficiency of the scheme are verified by comparison with the existing schemes and experiments.The CLA-VES scheme combines the benefits of certificateless signatures and aggregated signatures,aggregating the generated verifiable encrypted signatures into a fixed-size aggregated signature and solving key recovery and certificate management problems.Moreover,the scheme reduces signature communication and computation and improves verification efficiency compared with similar schemes.(2)A multi-party privacy-preserving fair contract signing protocol(MP~2FCSP)on the blockchain is designed based on the CLA-VES scheme.The protocol satisfies the requirements of fairness,privacy,immutability,timeliness and non-repudiation.Ethereum smart contracts are used to actualize as the offline trusted third party,which can achieve the goal of decentralization and fairness for the signature protocol.Moreover,the signatories jointly negotiate the blind factor to encrypt signature and contract content,which can solve the privacy-preserving problem in the contract signing process.Finally,we implement the protocol in Ethereum and verify the feasibility of the protocol by the Ethers cost of experiments.更多还原