On the Security of an Improved Identity-based Proxy Signature Scheme without Random Oracles

On the Security of an Improved Identity-based Proxy Signature Scheme without Random Oracles

Proxy signature can realize that an original signer delegates his/her signing right to a proxy signer. Then, the proxy signer can sign messages on behalf of the original signer when he/she is absent. The identity-based cryptosystem can simplify the costly certificate management. In this paper, we demonstrate that an improved identity-based proxy signature scheme in the standard model is not secure by giving four kinds of attacks. An improved scheme is also proposed to overcome the security flaws. Our improved scheme can be proved secure assuming the CDH problem to be hard. Performance analysis shows that our improved scheme is practical.