基于公开区块链的隐私保护公平合同签署协议  

A Privacy Preserving Fair Contract Signing Protocol based on Block Chains

作　　者：田海博[1,2] 何杰杰 付利青 

机构地区：[1]中山大学数据科学与计算机学院,广州510006 [2]广东省信息安全技术重点实验室,广州510006

出　　处：《密码学报》2017年第2期187-198,共12页Journal of Cryptologic Research

基　　金：国家自然科学基金项目(61672550);广东省自然科学基金项目(2015A030313133)

摘　　要：公平合同签署一直都是电子商务中一项重要的密码服务.现今的技术实践需要一个在线或离线的中心化可信第三方来解决合同签署中所出现的争端.但是中心化可信第三方具有较高的安全风险,较易出现单点故障,受到内部或者外部的攻击.作为比特币和许多其他数字货币的一项基础技术,区块链为我们提供了一个无中心的可信第三方,可以避免中心化可信第三方的问题,实现全球可信这样一个理想的目标.然而,基于区块链设计安全协议需要考虑区块链的公开验证和隐私保护之间的矛盾.基于区块链的安全协议一般是通过交易来完成协议的安全目标.而交易是公开的,区块链中每一个节点都可以读取交易数据,验证交易数据是否正确.如果交易数据中涉及隐私的内容,矛盾就产生了.特别的,对于公平合同签署协议,合同的签署人、内容、数字签名等都可能涉及敏感信息,往往是不希望公开的.那么在区块链上设计保护隐私的公平合同签署协议就是困难的.本文基于传统的可验证加密签名和盲签名思想,构造了盲的可验证加密签名体制,可以在公平合同签署这个应用场景中解决隐私保护的问题.我们基于该体制构造了公平且秘密的合同签署协议,可以让合同签署人通过区块链完成公平的合同签署,并且保护与合同相关的隐私内容.Fair Contract signing is always an important cryptographic service for electronic commerce. Current technique practices need an online or offline centralized trusted third party(TTP) to solve disputes appeared in a contract singing process. However, a centralized TTP has high risks. It may suffer the single point of failure, inside or outside attacks. The block chain, as a basic technique of Bitcoin and many other digital currencies, givesus a decentralized TTP, which could avoid many problems of a centralized one and may achieve the ideal goal of a global TTP. However, the contradiction should be considered between the public verification property of a block chain and the privacy protection requirement of a security protocol when we design such protocols based on block chains. A security protocol based on a block chain means that the protocol needs to fulfill its security goals through some transactions of the block chain. But the transactions are public. Every node of the block chain could read the transactions and verify the correctness of these transactions. If the transaction data involves privacy contents, a contradiction appears. Especially, for a fair contract signing protocol, the signers, contents and signatures of a contract may involve sensitive information and are not intended to be public. So it is hard to design a privacy preserving fair contract signing protocol based on block chains. This paper makes use of a blinded verifiable encrypted signature(VES) scheme based on traditional VES and the idea of blind signature. The new scheme could solve the privacy protection problem in the application scenario of fair contract signing. We give a fair and secret contract signing protocol based on the new scheme, which allows contract signers fulfill the task of fair contract signing based on public chains, and protects the privacy contents related to the contract.

关 键 词：区块链 公平合同签署 隐私保护 可验证加密签名 

分 类 号：F724.6[经济管理—产业经济] TP309[自动化与计算机技术—计算机系统结构] TP311.13[自动化与计算机技术—计算机科学与技术]