Comment: New digital signature scheme based on discrete logarithm

The purpose of this Comment is to show that the digital signature scheme based on the discrete logarithm problem proposed by Yen and Laih (ibid., vol. 29, no. 12, p. 1120-1, 1993) is vulnerable to substitution attack like other similar signature schemes based on discrete exponentiation in their basic form. It means that given a valid signature of a known message, it is computationally feasible to generate a valid signature of another different known message without the knowledge of the private key. Substitution is typically prevented by the use of a hash function or a redundancy generating function. >