关键词: 无证书签名, 恶意KGC攻击, 公钥替换攻击, 双线性对

Abstract: A certificateless signature scheme provably secure in the standard model is analyzed.It points out that the scheme is insecure.A kind of public key replacement attack against this scheme and an improved scheme is also analyzed and it shows that the attack is trivial and the improved scheme is vulnerable.A new malicious KGC attack called universal malicious KGC attack is given.In this attack，malicious KGC can generate the trapdoor system parameters of the schemes in set-up phase and forge signatures of any user for any message in the signing phase.A new improved scheme is presented to resist against this attack.

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