Reihaneh Safavi-Naini Yejing Wang Collusion Secure q-ary Fingerprinting for Perceptual Content. 57-75 2001 conf/ccs/2001drm Digital Rights Management Workshop http://link.springer.de/link/service/series/0558/bibs/2320/23200057.htm db/conf/ccs/ccsdrm2001.html#Safavi-NainiW01