中文摘要：

群签名使得群中任何一个成员均可以代表该群进行签名，而不会暴露签名者的身份。当争议发生时，签名者的身份可以通过群管理员公开。成员删除一直是群签名方案设计中难以解决的一个问题，何业锋等人最近在《软件学报》上提出了一个利用ELGamal加密和知识签名提出的一个动态群签名方案。指出该方案中被删除的群成员仍然可以作出签名，因而他们的方案是不安全的。

英文摘要：

Group signature allows an arbitrary member in a group can sign a signature on behalf of the group whilst the identity of the member remains anonymous, When a dispute investigation happens, the identity of the signer can be traced by the group manager. Member deletion is one of the kittlest problems in group signature schemes. “An Efficient and Secure Dynamic Group Signature Scheme”, He Yefeng and Zhang Jianzhong gave a method based on ELGamal encryption and signature of knowledge to solve the problem, in 2005. But we point out that in their scheme, the member who had been deleted from group can still give out a group signature that can pass the verification successfully, so there has some weakness in the security of their scheme.