Abstract: This paper analyzes a certificateless signature scheme, and points out the scheme can’t resist to the public key replacement attack and the malicious KGC（Key Generation Center） attack. The attacker can forge the signature for any message by substituting the public key of the signer. The malicious KGC can get the private key. The analysis shows that the scheme can not satisfy the safety requirements of the certificateless signature. Meanwhile the improvement measure is proposed to resist these attacks.

Key words: certificateless signature, public key replacement attack, malicious Key Generation Center（KGC） attack, bilinear pairing

摘要： 对一个无证书签名方案进行安全性分析，指出该方案不能抵抗公钥替换攻击和恶意的KGC攻击，即攻击者可以通过替换签名者的公钥来伪造任意消息的签名，恶意的KGC（Key Generation Center）可以获取用户的私钥。分析结果显示该方案不能满足无证书签名方案的安全性要求，同时为了应对这两种攻击，提出了改进的方案。

关键词: 无证书签名, 公钥替换攻击, 恶意密钥生成中心（KGC）攻击, 双线性对