中文摘要：

通过对Zhang-Liu-He（2006）,Gan-Chen（2004）和Wang-Zhang-Ma（2007）提出的可转换环签名方案进行分析,指出了这几个可转换环签名方案存在可转换性攻击或不可否认性攻击,即,环中的任何成员都能宣称自己是实际签名者或冒充别的成员进行环签名。为防范这两种攻击,对这几个可转换环签名方案进行了改进,改进后的方案满足可转换环签名的安全性要求。

英文摘要：

The security of the three convertible ring signature schemes proposed by Zhang-Liu-He （2006）, Gan-Chen （2004） and Wang-Zhang-Ma（2007） is analyzed, and it is found that these convertible ring signature schemes are susceptible to convertibility attack or non-repudiation attack, i.e., any member in the ring can claim that he is the actual signer or pretend others＇ identity to sign message. To guard against the attack, these convertible ring signature schemes are improved, which can make the improved schemes satisfy the security requirements for convertible ring signature.