Yoshikazu Hanatani Yuichi Komano Kazuo Ohta Noboru Kunihiro Provably Secure Untraceable Electronic Cash against Insider Attacks. 980-991 2007 90-A IEICE Transactions 5 http://dx.doi.org/10.1093/ietfec/e90-a.5.980 db/journals/ieicet/ieicet90a.html#HanataniKOK07