Forgery attacks on digital signature schemes without using one-way hash and message redundancy

Chang and Chang proposed a new digital signature scheme, and claimed the scheme can resist the forgery attack without using one-way hash function and any redundancy padding. This claim is very interesting to all designers, because conventionally a one-way hash function is required to resist the attacks. This article shows an existential forgery attack on the scheme, and shows that the scheme would still be insecure even if a secure one-way function were adopted in the scheme.