Abstract：Qi Ming and others recently analyzed and discussed the security of two kinds of the ElGamal signature schemes and the password authentication scheme based on two kinds of the signature schemes,and proposed two kinds of improved schemes.This paper first points out that the first p type signature scheme proposed by Qi is not secure,since attackers can forge signature for any message.Then this paper shows that the generalized ElGamal signature schemes can not resist the substitution attack.Finally this paper shows that two kinds of the improved schemes proposed by Qi can not resist the homomorphism attack,and does not have the security as Qi said.
2000, Vol. 22 
