Analysis and Improvement for A Class of Forward Security Digital Signature Scheme

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.