Methods and apparatus for efficient revocation of receivers. In one implementation, a method of broadcast encryption includes: assigning a respective master key to each of a plurality of receivers, where each master key can be used to derive two or more of a plurality of sub keys; revoking one or more...http://www.google.com.tw/patents/US7757082?utm_source=gb-gplus-share專利 US7757082 - Efficient revocation of receivers
