Abstract: Two identity-based designated verifier signature schemes, which were proposed by Zhang and Li-Zheng-Zhu respectively, were analyzed. It was shown that two schemes did not satisfy the security requirements of designated verifier signature. Zhang's scheme did not meet the unforgeability requirement; Li-Zheng-Zhu's scheme did not have designated verification as although the non-designated-verifier could check the validity of the signatures. Then the schemes were improved. The improved Zhang's scheme owns unforgeability property, and has the same efficiency as the Zhang's. The improved Li-Zheng-Zhu's scheme owns designated verification property; moreover, the improved scheme has reduced one bilinear paring and is more efficient than the Li-Zheng-Zhu's.

Key words: identity-based signature, designated verifier signature, short signature, bilinear pairing

摘要： 分析了两个基于身份的指定验证者签名方案（Zhang方案和Li-Zheng-Zhu方案），指出了两个签名方案不满足指定验证者签名的安全特性：Zhang方案不满足不可伪造性，Li-Zheng-Zhu方案中非指定验证者可以验证签名的有效性，不满足指定验证性。对两个方案进行了改进，改进后的Zhang方案满足不可伪造性，并具有与原方案相同的效率；改进后的Li-Zheng-Zhu方案不仅满足指定验证性，而且减少了一个双线性对运算，具有较高的效率。

关键词: 基于身份签名, 指定验证者签名, 短签名, 双线性对