Nonrepudiable Proxy Multi-Signature Scheme

The concept of proxy signature introduced by Mambo, Usuda, and Okamoto allows a designated person, called a proxy signer, to sign on behalf of an original signer. However, most existing proxy signature schemes do not support nonrepudiation. In this paper, two secure nonrepudiable proxy multi-signature schemes are proposed that overcome disadvantages of the existing schemes. The proposed schemes can withstand public key substitution attack. In addition, the new schemes have some other advantages such as proxy signature key generation and updating using insecure channels. This approach can also be applied to other ElGamal-like proxy signature schemes.