Signature scheme based on discrete logarithm without using one-way hash-function

Contrary to Shao´s claim for developing a signature scheme based on a discrete logarithm without using a one-way hash function (see ibid., vol.34, no.11, pp.1079-80, 1998), we have shown that Shao´s scheme is vulnerable to homomorphism attacks. The main justification for the use of Shao´s scheme is its resistance to homomorphism and substitution attacks. Substitution attacks can be avoided by the use of a one-way hash-function, and so there appears to be no reason to use Shao´s scheme. Although the Elgamal scheme and its variants (e.g. DSS) are subject to homomorphism attacks, the success of such an attack appears to be no more likely than finding a discrete logarithm, as long as the random integer used to construct the signature is chosen at random