Ying Sun Chunxiang Xu Qi Xia Yong Yu Analysis and Improvement of a Proxy Blind Multi-signature Scheme without a Secure Channel. 661-664 2009 IAS http://dx.doi.org/10.1109/IAS.2009.167 conf/IEEEias/2009 db/conf/IEEEias/IEEEias2009.html#SunXXY09