This paper shows that the two short signature schemes provably secure in the standard model are all insecure against key substitution attacks under the multi-user setting,namely an adversary can generate a new public key satisfying legitimate signatures created by the legitimate signer.

Through the cryptanalysis of a threshold proxy signature scheme in literature,the scheme could not resist insider attacks and public-key substitute attacks.

Through the cryptanalysis of a new threshold proxy signature scheme based on bilinear pairings,it is found that the scheme can t resist forgery attack and public-key substitute attack.

Through the cryptanalysis of threshold proxy signature scheme proposed by Huang et al(denoted as HC scheme) recently,it is found that the scheme could not resist frame attacks and public-key substitute attacks.

That a presented proposal of efficient certificateless signature scheme is insecure against public key replacement attack is demonstrated.

It is found that the three schemes are all insecure against public key replacement attack.

The certificateless signature scheme can suffer from public key replacement attack so that any one can forge a valid signature on any message.

Assuming that the encoding rules are chosen according to a uniform probability distribution, the probabilities P I and P S of a successful impersonation attack and a successful substitution attack, respectively, of this code are also computed.

On assuming that encoding rules are chosen according to a uniform probability distribution,the probabilities of a successful impersonation attack and a successful substitution attack of these codes are also computed respectively.

Assuming that the encoding rules are chosen according to a uniform probability distribution, the probabilities P I and P S of a successful impersonation attack and a successful substitution attack, respectively, of this code are computed.