Cryptanalysis of a proxy-protected proxy signature scheme based on elliptic curve cryptosystem

Proxy signature allows original signer to delegate his/her signing capability to proxy signer such that the proxy signer can sign messages on behalf of the original signer. Based on elliptic curve, one can obtains better efficiency compared to conventional proxy signatures. But in any case, take security into account, a good signature scheme should he designed to meet its basic security requirements. In this paper, we present an original signer forgery attack on an elliptic curve based proxy signature proposed recently by Chen, Liu, and Chung. By firstly constructing a forged proxy signature key pair, the attack is successful in forging signatures on any message. An improvement is presented to be secure against the proposed attack and the efficiency is comparable to the original scheme.