Cryptanalysis of Nonrepudiable Threshold Proxy Signature Schemes with Known Signers

[[abstract]]In 2000, Hwang et al. proposed a nonrepudiable threshold proxy signature scheme to improve Sun’s scheme. In this paper, a new attack is proposed to show that, both in Hwang et al.’s and Sun’s schemes, the threshold proxy signatures can be forged by the cooperation of only one proxy signer and the original signer