Guilin Wang Sihan Qing Mingsheng Wang Zhanfei Zhou Threshold Undeniable RSA Signature Scheme. 221-232 2001 conf/icics/2001 ICICS http://link.springer.de/link/service/series/0558/bibs/2229/22290221.htm db/conf/icics/icics2001.html#WangQWZ01