Proxy Signature Scheme Secure against Chosen Key and Chosen Warrant Attacks

An enhanced security model for proxy signature schemes is formalized. In the new model, we consider chosen key and chosen warrant attacks which exist in real environment but were neglected in previous security models. Then we propose a proxy signature scheme from bilinear maps. The proposed proxy signature scheme is based on a secure signature schemes which is used for computing the standard signature, delegating the signing rights and computing proxy signature. Finally, we present a security proof of the proposed proxy signature scheme by reducing directly the security of the proxy scheme to the basic signature scheme. The proposed proxy signature scheme has the shortest proxy signatures.