Improvement of Nonrepudiable Threshold Proxy Signature Scheme

On the basis of YTH threshold proxy signature scheme, a nonrepudiable scheme with known signers was constructed by Hu et al. in 2009. They claimed that the weaknesses of frame attack, collusion attack and public-key substitute attack can be overcome in their scheme. Whereas this article will demonstrate two security leaks of frame attack and collusion attack inherent in Hu et al.´s threshold proxy signature scheme, which is not as same as they claimed, previously. That is, the original signer can forge a valid threshold proxy signature while the proxy group doesn´t know it, and any t or more proxy signers could cooperatively reconstruct the secret polynomial function f(x) to fake a proxy signature. In this article, based on Hu et al.´s scheme, we propose a new and efficient scheme to resist those attacks.