Weidong Qiu Mingxing He Firoz Kaderali Group Oriented Digital Certificate Architecture. 233-237 2003 conf/wecwis/2003 CEC http://csdl.computer.org/comp/proceedings/cec/2003/1969/00/19690233abs.htm db/conf/wecwis/cec2003.html#QiuHK03