An Improved Nonrepudiable Threshold Proxy Signature Scheme with Known Signers

Xin Liu1,2, Qiu-Liang Xu1, Jiu-Qing Shang3 1(School of Computer Science and Technology, Shandong University, Jinan, 250061, China) 2(Department of Information Engineering, Shandong Youth College, Jinan, 250014, China) 3(Shijiazhuang Mechanized Infantry Academy, Shijiazhuang, 050083,China) 1 lxonne@163.com, 2 xql@sdu.edu.cn, 3 shangjiuqing@163.com Abstract In a (t, n) threshold proxy signature scheme, n proxy signers of a designated group are given secret shares such that t or more of them can cooperatively sign messages on behalf of the original signer, but t-1 or less of them cannot do this. In 1999, Sun suggested a nonrepudiable threshold proxy signature scheme with known signers. Later, Sun\´s scheme was found to be vulnerable to the conspiracy attack. By proposing a variant of the so-called "signatures of knowledge", we present a new nonrepudiable threshold proxy signature scheme. The unforgeability against active adversaries is proved under the random oracle model. Furthermore, we stress that the new scheme satisfies all main properties of a practical and secure (t, n) threshold signature scheme.