Improvement of M-U-O and K-P-W proxy signature schemes

The concept of proxy signature introduced by Mambo, Usuda, and Okamoto allows a designated person, called a proxy signer, to sign on behalf on an original signer in 1996. However, most existing proxy signature schemes does not support nonrepudiation. We propose two secure nonrepudiable proxy signature schemes, which overcome disadvantages of M-U-O and K-P-W proxy signature schemes, respectively. The schemes proposed can withstand public key substitution attack and forge attack. In addition, our new schemes have some other advantages such as proxy signature key generation and updating using insecure channels. Our approach can also be applied to other ELGamal-like proxy signature schemes.