安全电子投票协议设计与分析

A secure voting system is designed to protect the anonymity of voters, while at the same time guarantee the validity of the voting, and assure that the voting is cast accurately. The more challenging subject is that, how to achieve two goals that seem conflict, i.e. a voter could verify whether his voting is recorded and counted correctly, while he has no evidence to prove that his ballot has been cast to a certain candidates, which prevents the voter from selling votes. Based on Shamir's secret sharing, the research aims to achieve the following security properties: verifiability, receipt-freeness, and coercion-resistance. First of all, we will propose the trust assumption and adversary assumption in which a trusted third party is not necessary, which eliminates the bottleneck due to relying on the trusted third party, and makes the protocol more robust. Secondly, under the security model, we will design secure e-voting protocols, in which a voter owns no additional information to verify the correctness and eligibility without others' help. Even if a malicious voter equipped with secret device launches side channel attack, he can get nothing to prove which candidate has been selected. In addition, an e-voting protocol should resist subliminal channel attacks. Furthermore, we will try to do a more challenging work, which is to construct an information-theoretically secure e-voting protocol. The results of the project will promote the design of security model and the secure e-voting protocols that don't rely on a trusted third party, and guarantee the security of e-voting.

安全电子投票协议要求在保证投票者匿名性的同时，实现投票的合法性和计票的准确性。更有挑战性的是，如何实现一对看似矛盾的目标：既保证投票者能够验证自己的结果是否被正确计票，又使投票者无法向他人证明自己投了特定候选人的票，以防止选票买卖。本项目拟以Shamir的秘密共享为基础，实现投票结果的可验证性、选票的无收据性、并能抵抗胁迫攻击。主要包括：研究无可信第三方的信任模型与攻击模型，消除由于可信第三方造成的安全瓶颈，提高协议的健壮性；以安全模型为基础，设计满足安全目标的电子投票协议，使得投票者可验证自己的意图是否被正确记录及正确计票，即使恶意投票者发起边信道攻击，也无法获得额外的信息向他人证明选票内容，以抵抗各种胁迫攻击。此外，探索具有信息理论意义上安全性的电子投票协议设计。该项目的成果，能够促进无可信第三方的安全模型及安全电子投票协议的研究，保障电子选举活动的顺利进行。

安全电子投票协议对于学术界、技术界都有很大的挑战，主要是因为要同时实现两个看似矛盾的目标：计票结果的正确性检验、无法向他们证明投票内容以避免胁迫攻击。可以使用的密码学工具包括：同态加密、秘密分享、零知识证明、k-匿名等。同时，安全电子投票协议也可以看作具有隐私保护性的数据聚合，而后者正在大数据时代的一个重要研究内容，不同点在于前者需要准确聚合，而后者在很多情况下容许一定的误差。本项目的研究内容包括：抗胁迫攻击的安全电子投票协议，基于k-匿名的安全电子投票协议，具有隐私保护性的数据聚合协议，轻量级认证协议及抗内部人攻击的认证协议，数据的分布式存储及恢复研究，同态加密研究，抗量子计算机攻击的密码协议研究等。针对现有方案的不足和漏洞，进行了系统分析，提出了其存在的安全性风险：不能抵抗侧信道分析，不能事后验证。并对其系统模型，协议流程进行了改进。文章A Robust Electronic Voting Scheme Against Side Channel Attack发表在 Journal of Information Science and Engineering。在具有隐私保护性的数据聚合协议方面的研究，主要采用差分隐私、分布式解密、有条件的离散对数可解等基础，提出了满足设计要求的安全协议。成果发表在 KSII Transactions on Internet and Information Systems. Vol. 10, no. 8, pp. 3852-3864, 2016. 另外，A Practical Privacy-Preserving Data Aggregation (3PDA) Scheme for Smart Grid投稿到IEEE Transactions on Industrial Informatics（Major Revision）。同态加密被广泛用于电子投票或数据聚合，我们对其的研究成果发表在IEEE Transactions on Information Forensics and Security,和计算机应用。对在物联网时代的抗量子计算机攻击的密码算法的综述发表在IEEE Communication Magazine。