Cryptanalysis of a signature scheme without using one-way Hash functions
一个无单向Hash函数的签名方案的安全性分析

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.