Convertible Proxy Signature Scheme

Abstract

In this paper, we propose a new type of proxy signature, called convertible proxy signature scheme. A convertible proxy signature scheme allows a proxy signer to sign a message on behalf of an original signer. The proxy signer can create a valid proxy signature for the original signer. However, the identity of the proxy signer isn't exposed to any other third party from the proxy signature. To avoid a dispute, the proxy signer must have the capability of proving, to any arbitrator, that he is the actual proxy signer of a valid proxy signature. On the contrary, a proxy signer must also have the capability of proving, to any arbitrator, that he isn't the actual proxy signer of a valid proxy signature which is created by others. In case of necessity, the original signer or the proxy signer can convert the proxy signature into a new proxy signature in which the identity of the proxy signer is disclosed. Based on the discrete logarithm problem, a concrete convertible proxy signature scheme is realized in this paper.