中文摘要：

对于S-H．Seo等提出的无证书代理签名方案进行了密码分析，给出了一个有效的伪造攻击算法，指出此方案不能抵抗第二种类型敌手的攻击，敌手Ⅱ可以伪造任意消息的合法代理签名。最后分析了此方案遭受攻击的主要原因，并给出了相应的改进措施。

英文摘要：

Recently, S-H. Seo et al proposed a certificateless signature scheme and used it to construct a certificateless proxy signature with provable security. They demonstrated that their schemes are provable security in the random oracle model under the computational Diffie-Hellman assumption. Unfortunately, by given concrete attack, the paper demonstrated that their schemes were not secure against the Type Ⅱ adversary. A Type Ⅱ adversary could forge a legal proxy signature of any message. The paper analyzed the root cause of attack and gave some suggestions for modifications in the end.