Improvement on Huang et al.'s Novel Efficient Threshold Proxy Signature Scheme

In 2006, Hui-Feng Huang and Chin-Chen Chang proposed a novel efficient threshold proxy signature scheme based on Schnorr's scheme. In their scheme, the original signer could know who generated the threshold proxy signature and the receiver could certify the actuality of the proxy group signers who made the proxy signature. However, their scheme had some security weaknesses. In this paper, by identifying some concrete instances and analyzes, we demonstrate that their scheme is vulnerable to the forgery attack and the public-key substitute attack. That is, Huang et al.'s scheme could not achieve their claimed security requirement. Finally, we propose our improvement to eliminate the weaknesses and give its security analysis.