基于双线性对的具有已知签名人的门限代理签名方案

（t，n）门限代理签名是代理签名的一种变形，其代理签名密钥由原始签名者指定n个代理签名者分享保存，只有t个或更多的代理签名者才能代表原始签名者产生对消息的签名。最近，钱海峰等人提出了一个基于双线性对的门限代理签名方案。不幸的是。本文显示了钱海峰等人的方案易受伪造攻击，即一小敌手能够伪造任意消息的门限代理签名。此外，钱海峰等人的方案还存在代理签名者能够任意更改门限值这一缺陷，而对此无论是原始签名者还是验证者都无法发现，这一点可能违背原始签名者的意图。本文提出了一个新的门限代理签名方案，新方案克服了钱海峰等人的上述缺陷。

A threshold proxy signature scheme with known signers from bilinear pairings

In a（t, n） threshold proxy signature scheme, which is a variant of the proxy signature scheme, the proxy signature key is shared among a group of n proxy signers delegated by the original signor. Any t or more proxy signers can cooperatively sign messages on behalf of the original signer. Recently, Qian et al. proposed a new threshold proxy signature scheme from bilinear pairings. Unfortunately, we s~how that Qian et al.＇s scheme is vulnerable to the forgery attack. That is, an .adversary can forge a valid threshold proxy signature on any messages. In addition, Qian et al.＇s scheme suffers from the weakness that the proxy signvrs might change the threshold value. That is, the proxy signers in the designated proxy group can arbitrarily modify the threshold stratogy without being detected by the original signer or verifiers, which might violate the original signer＇s intent. In this paper, we propose a new threshold proxy signature scheme that overcomes the above weaknesses.