摘要： 已有的前向安全签名方案大都基于因子分解困难性问题。吴克力和秦波等人分别提出了一种基于离散对数难题的前向安全签名方案，但该类方案中时段参数在验证过程并不是一个有效的参数，若某个时段的私钥泄露，可用该私钥来伪造在此以前的任何时间段的签名，因而该类方案并不具备前向安全性。该文在吴方案的基础上提出了一种新的基于ElGamal体制的前向安全签名方案，该方案将当前私钥隐藏在签名中，验证时必须有效使用时段参数，以确保签名具有前向安全性。该方案中所用方法也适用于改进秦的方案。

关键词: 前向安全, ElGamal签名, 数字签名

Abstract: Forward security digital signature schemes existed are mostly based on difficulty of factoring. Qin Bo and Wu Keli et al. proposed a forward security digital signature scheme based on discrete logarithm respectively. This paper points out this class of scheme is not forward secure, because its time-parameter is not a valid parameter when its validity is verified. If a secret key is revealed, adversary can forge a valid digital signature in any time period with the current secret key. This paper proposes a new forward security signature scheme based on ElGamal scheme. The scheme embeds the current private key in the signature, and time-parameter is necessary when its validity is verified. The method in the new scheme can also be applied to Qin’s scheme.

Key words: Forward security, ElGamal signature, Digital signature