Lys98群盲签名方案的一个安全缺陷及其改进

A Security Drawback of Group Blind Signature Lys98 and Its Improvements

1998年Lysyanskaya和Ramzan在国际金融密码会议(FC98)上,将群签名和盲签名结合起来提出第一个群盲签名方案(Lys98),他们认为该方案能够满足抗联合攻击等多种安全需求。本文首先指出Lys98方案是不能抵抗联合攻击的,然后针对它的成员加入协议给出一个简单的联合攻击方案。该攻击证明了在成员加入阶段个别群成员勾结起来可以伪造能产生合法群签名但却无法被跟踪的成员证书。最后本文针对该攻击提出两个改进方案。

At the international financial cryptograph conference in 1998（FC98）, Lysyanskaya and Ramzan introduced a new cryptograph scheme called a Group Blind Signature Lys98, which combined, for the forst time, the existing notions of a group digital signature and a blind digital signature. They considerd their scheme possible to satisfy multed security requirements to resisit coalition attacks. We have found that Lys98 is not able to resist coalition attacks. Some collection of group members may collude and combine their secret membership keys in such a manner that they generate a valid, yet untraceable group signature. In the end of the paper two modified schemes are presented to prevent this kind of attack.