TWC: Small: Empowering Anonymity

匿名凭证系统允许用户在不透露其身份的情况下证明他/她是被授权的，并且进一步地，在不泄露附加信息的情况下获得附加凭证。在传统的匿名证书系统中，当证明拥有证书时，必须透露其颁发者。这可能是一个问题：将关于用户居住地的信息(基于谁颁发了他/她的驾照)与他/她的雇主是谁(基于谁授权他/她在特定的车库停车)以及他/她的年龄(可能在特定交易的上下文中透露)放在一起可能会导致该特定用户的身份识别，即使他/她使用的是匿名凭据！可委托的匿名凭据系统消除了这一问题。它允许用户委派他们的匿名凭据；例如，公司员工可以使用他/她的员工凭据向公司访客颁发访客通行证，公司访客可以向前来接他/她的出租车服务颁发凭据；不同的参与者(员工、他/她的客人和他/她的司机)不需要透露任何关于他们自己的持久标识-或者实际上任何东西。这个项目旨在演示以下论点：使用非匿名凭据可以完成的一切也可以使用可委托的匿名凭据来完成。这包括有用的附加功能，如凭据属性(如过期日期)、属性和身份托管、条件匿名性(因此，违反服务条款会导致身份识别)和凭据吊销。

An anonymous credential system allows a user to prove that he/she is authorized without revealing his/her identity, and, further, to obtain additional credentials without revealing additional information. In a traditional anonymous credential system, when demonstrating possession of a credential, it is necessary to reveal its issuer. This can be a problem: putting together the information about where the user lives (based on who issued, say, his/her driver's license) together with who his/her employer is (based on who authorized him/her to, say, park in a particular garage) together with his/her age (which might be revealed in the context of a particular transaction) may lead to the identification of this particular user, even though he/she is using anonymous credentials! A delegatable anonymous credential system eliminates this problem. It allows users to delegate their anonymous credentials; for example, a company employee can use his/her employee credential to issue a guest pass to a company visitor, who can in turn issue a credential to a taxi service that comes to pick him/her up; the various participants (the employee, his/her guest, and his/her driver) need not reveal any persistent identifiers - or in fact anything - about themselves. This project aims to demonstrate the following thesis: Everything that can be done with non-anonymous credentials can also be done with delegatable anonymous credentials. That includes useful additional features such as credential attributes (such as expiration dates), attribute and identity escrow, conditional anonymity (so that violating terms of service leads to identification) and revocation of credentials.