Abstract: This paper analyzes the security of the certificateless proxy signature scheme that Liu Xiaohong and Zhang Jianzhong proposed. The analysis shows that Liu and Zhang’s scheme cannot resist the attack of malicious KGC and the collusion attack among the original signer, the proxy signer and KGC. To get over these security problems, an improved scheme is proposed. The security analysis shows that the improved scheme can overcome the above mentioned problems.

Key words: proxy signature, certificateless signature, collusion attack, bilinear pairing

摘要： 分析了刘晓红和张建中提出的一个无证书代理签名方案，发现其不能抵抗恶意KGC攻击、原始签名人A（代理签名人B）和KGC的合谋攻击。针对这些安全问题，提出了一种改进方案，分析表明：改进方案能克服以上的安全性问题。

关键词: 代理签名, 无证书签名, 合谋攻击, 双线性对