一个无单向Hash函数的签名方案的安全性分析

摘要

2004年,Chang等提出了一种不使用单向Hash函数和消息冗余度的数字签名方案.但是Zhang指出他们的方案存在伪造攻击.为了克服Zhang的攻击,Zhang等基于Chang的签名方案提出了一个改进方案,并且对改进的签名方案进行了安全性分析.然而,通过给出一种简单的攻击,指出Zhang等的方案仍是不安全的.为了抵抗这种攻击,Hash函数和消息冗余度可能仍旧需要作用.%In 2004, Chang, et al. proposed a digital signature scheme without using one-way hash function and message redundancy schemes. But Zhang showed that the scheme can be forged. In order to overcome Zhang's attack, Zhang, et al. demonstrated an improved signature scheme based on Chang,et al. 's signature scheme and analyzed the security of the improved scheme. But in this paper, we identify a simple attack to show Zhang, et al.'s scheme is still not secure. To resist this attack, the hash function and message redundancy schemes may be still used.