电子身份证件系统中支持高效属性证明的可审计匿名凭证方案研究

Electronic Identity Card, eID, is an infrastructure for trusted digital identities in cyber space, where anonymous credential system is the cryptographic key technique to solve the increasing privacy issue in eID systems. However, the existing anonymous credential systems are not practical to the eID application due to accountability and attributes proof efficiency. The proposal will define accountability from the ability of revealing dishonest user's privacy through multi-granularity revocation. Regarding the attributes proof efficiency, attributes are classified into strong and weak, dependent on whether they are supposed to be hidden from the issuer, i.e., whether the issued credential is full anonymous. The whole efficiency of attributes proof will be improved through the light encoding and proof of weak attributes. Furthermore, aggregate signature definition is adopted to solve attributes proof with linear complexity. Accordingly, the proposal will firstly focus on the cryptographic primitives for constructing efficient attributes proof-enabled anonymous credentials, and research on the verifiable message-holder identity-embedded selective aggregate signature scheme. Secondly, construct an issuance protocol for accountable anonymous credential, present the strong-weak differentiated attributes encoding method and multi-granularity revocation oriented accountability model. Furthermore, the proposal will address attributes proof in accountable anonymous credential, construct protocols of logic and comparison relation proof over strong and weak attributes, based on selective aggregate signature. The experiment will give efficiency analysis with respect to the number of exponentiations and pairings, and publish the concrete performance data gathered in the simulated Java smart card and NFC environment and applications. The output of the proposal will offer a brand-new idea and scheme to address accountability of anonymous credential and attributes proof efficiency issues, and contribute a practical anonymous credential scheme to the privacy-preserving eID system.

电子身份证件(eID)是网络空间可信数字身份基础设施，匿名凭证是解决eID隐私保护问题的密码学关键技术，然而属性证明效率和凭证可审计性问题降低了匿名凭证在eID系统中的实用性。本项目根据对隐私的敏感程度区分强、弱属性，利用聚合签名思想设计高效属性证明协议，从隐私性撤销的角度建立面向多粒度撤销的凭证可审计性实现方法，从而为eID系统提供一套安全高效的匿名凭证方案。首先研究支持高效属性证明的匿名凭证密码学原语，在随机预言模型下和标准模型下构造可证消息持有者身份的选择性聚合签名方案，在此基础上研究可审计匿名凭证的签发机制，建立面向多粒度撤销的凭证审计模型，最后研究可审计匿名凭证中的高效属性证明方法，设计基于选择性聚合签名方案的属性逻辑关系和比较关系证明协议。项目的成功实施将为解决属性证明效率和匿名凭证可审计性问题提供新思路和新方法，为提高匿名凭证在eID系统中的实用性提供密码学理论依据。

随着电子商务、电子政务、健康医疗、社交等事务已逐渐转移到互联网应用中进行，在方便用户的同时也在不断的将越来越多的用户身份信息进行收集、分析和分发。如果对这些敏感的身份信息不加以保护，将会给用户带来人身和财产安全上的风险。首先，用户对留存在服务提供商的身份信息失去了控制权，这些信息一旦被服务提供商所滥用将会直接骚扰用户的日常生活；此外，服务提供商所收集的大量用户信息容易成为攻击者的目标，一旦被攻击者获取将会导致隐私泄露，甚至产生身份盗用的严重后果。本项目研究并提出了一种隐私保护属性证明系统ABPass，以eID为基本框架，构造了一系列基于匿名凭证的属性证明协议，采用承诺方案、知识的零知识证明技术及数字签名等密码学原语，支持多个属性之间的复合逻辑关系证明，以满足在线服务对细粒度身份认证和访问控制的需求。采用聚合签名思想解决属性证明线性复杂度问题。研究并提出了基于短签名方案和零知识证明技术的属性证明协议，在随机预言模型下和标准模型下分别构造了面向有限集类型属性的AND、OR、CNF证明协议以及面向整数类型属性的不等式证明协议。采用基于短签名方案的扩展BLS+短签名方案，适合用于资源有限的移动终端设备。此外，项目从用户信誉入手分析匿名凭证可审计性问题，研究并提出了基于可撤销假名的凭证审计机制，建立了用户行为与信誉值之间灵活的关联关系，根据惩罚策略的轻重对不同程度的违规行为进行不同程度的撤销。基于跨窗口的方法设置了撤销时长，并构建了跨窗口黑名单，通过用户身份对跨窗口撤销用户进行关联，以此来增强撤销机制的灵活性。本项目给出了ABPass在视频服务中的应用场景及原型系统，以视频分级策略为例，要求用户对多个属性之间的复合逻辑关系进行证明。实际运行结果表明，ABPass系统可以在移动终端上有效实现细粒度的匿名身份验证过程，从而为隐私保护的数字身份管理领域提供一种轻量的、实用的解决方案。