Qingshui Xue Fengying Li Yuan Zhou Jiping Zhang Zhenfu Cao Haifeng Qian Bilinear-pairings Based Designated-verifier Threshold Proxy Signature Scheme. 323-327 2009 Security and Management conf/csreaSAM/2009 db/conf/csreaSAM/csreaSAM2009.html#XueLZZCQ09