一种前向安全数字签名方案的分析与改进

CRYPTANALYSIS AND IMPROVEMENT OF A FORWARD SECURITY DIGITAL SIGNATURE SCHEME

对于前向安全数字签名方案,即使签名密钥在j时段被盗,窃密者也仅能伪造j时段后的有效签名,而j时段前的签名仍然有效。针对文献[10]提出的一种具有前向安全的数字签名方案进行了安全性分析,发现该方案存在安全隐患,不具有前向安全性:窃密者一旦盗取了j时段的密钥,即可伪造任一时段的有效签名。在文献[10]的基础上,提出了一种新的前向安全数字签名方案,并对该方案进行了详细的安全性分析。新方案的特点是将当前密钥隐藏在签名中,仅使用与当前密钥有关的信息对消息进行签名,与后继密钥无关,签名的前向安全性基于离散对数和模合数平方根问题的难解性。

For a forward security digital signature scheme, even if the secret key is leaked out at period j, an adversary obtained it can only forge the valid signature after period j but the signature before period j is still valid. Through the security analysis of a forward security dig- ital signature scheme proposed in reference [ 10 ] , in this paper it points out the scheme mentioned above has hidden insecurity and no forward security： An adversarial stealer can forge a signature valid at any time as long as he/she obtains the secret key for a given period j. According to reference [ 10] , a new forward security digital signature scheme based on ElGamal scheme is proposed, and the security of this proposed scheme is analyzed in detail. The characteristic of this new scheme is that to embed the current secret key in signature and only sign the message by the indication with regard to current secret key. The course of the signature scheme bears no relation to the subsequent secret key. The scheme is proven to be forward secure, which is based on the abstrusity of discrete logarithm and square rood modulo composite number problem.