An improved signature scheme without using one-way Hash functions

Recently, Chang et al. give a digital signature scheme, where neither one-way hash function nor message redundancy schemes are used, but Zhang et al. has shown that the scheme was forgeable, namely, any one can forge a new signature by the signer's signature, and give two forgery attacks. To the above attacks, we give an improved signature scheme based on Chang signature scheme and analyze the security of the improved scheme.