中文摘要：

基于身份的数字签名是一种重要的密码学工具，不仅在基于身份密码体制中实现了签名功能，而且简化了传统数字签名中公钥证书的生成、管理和吊销等问题．Paterson和Schuldt首次构造了标准模型下可证明安全的基于身份的数字签名方案，但是该方案效率不高且通信代价昂贵．李继国和姜平进提出了一个新型的改进方案---标准模型下可证安全的基于身份的高效签名方案，新方案的特点是：标准模型下可证明安全、计算效率更高、通信代价更小．然而，文中发现，该方案并不满足不可伪造性，原因在于用户密钥提取是广义伪造的．进一步指出了原方案安全性证明中的缺陷：敌手的view与安全性模拟中成功的事件不独立．

英文摘要：

An identity-based signature is an important cryptographic primitive which can realizethe functionality of signing in identity-based cryptography and can also simplify the key manage-ment procedures including the generation,management and revocation of digital certificates in thetraditional digital signatures.The first identity-based signature that can be proven secure in thestandard model was proposed by Paterson and Schuldt,unfortunately,the scheme suffers fromlow efficiency in computation and heavy cost in communication.An improvement due to Li andJiang was given,and the scheme was claimed as being provably secure in the standard model,enjoying shorter signature length and less computation operation.However,in this paper,wedemonstrate that the new scheme is insecure against the forgery attack by providing a concretesecurity analysis in their security model.This attack is due to the universal forgery of the keyextraction in their scheme.We also show the flaws in their security proof：the view of the adversaryis not independent of the event that the simulation succeeds.