Abstract: Analysis shows that two proxy signature schemes based on braid groups are insecure: the first scheme cannot resist the original signer’s change attack; in the scheme of second, any antagonist can successfully forge a valid proxy signature scheme, which the antagonist can designate any proxy signer and messages. Later, a new proxy signature scheme was proposed. Analysis shows that the proposed scheme satisfies all security requirements; what’s more, no security channel is in need in the communication of the original signer and the proxy signer.

Key words: braid group, proxy signature, forgery attack, security analysis, conjugacy search problem

摘要： 对两个基于辫群的代理签名方案进行了分析，发现它们并不满足不可伪造性。第一个方案中不能抵抗原始签名人改变攻击，在第二个方案中任何攻击者可以伪造一个有效的代理签名，在该签名中，代理签名者以及消息可以任意指定。根据上述缺陷，提出一个改进的强代理签名方案， 新方案在不增加计算复杂性的前提下，保证了签名的安全性，同时代理授权过程中还增加了不需要安全通道的性质。

关键词: 辫群, 代理签名, 伪造攻击, 安全分析, 共轭查找问题