中文摘要：

通过对一个标准模型下可证安全的无证书签名方案进行分析,指出该方案是不安全的。分析了一种针对该方案的公钥替换攻击和改进方案,说明该公钥替换攻击是一种平凡的伪造攻击,指出了这个改进方案也是不安全的。提出了一种新的密钥生成中心KGC攻击,即通用恶意KGC攻击,在这种攻击下,这两个无证书签名方案的KGC总是能够在系统参数生成阶段生成包含陷门信息的系统参数,利用这些参数,KGC不需要计算出用户的私钥就可以冒充任意系统用户对任意消息进行伪造签名。给出了攻击方法,并针对这种通用恶意KGC攻击提出了新的改进方案,使其能够抵抗这种攻击。

英文摘要：

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.