A method is disclosed for a device to interdependently validate a digital content package having a piece of digital content in an encrypted form, and a corresponding digital license for rendering the digital content. A first key is derived from a source available to the device, and a first digital signature...http://www.google.com.tw/patents/US7680744?utm_source=gb-gplus-share專利 US7680744 - Method for interdependently validating a digital content package and a corresponding digital license
