David W. Kravitz Kim-Ee Yeoh Nicol So Secure Open Systems for Protecting Privacy and Digital Services. 106-125 2001 conf/ccs/2001drm Digital Rights Management Workshop http://link.springer.de/link/service/series/0558/bibs/2320/23200106.htm db/conf/ccs/ccsdrm2001.html#KravitzYS01