Content data encrypted with a content key, the content key encrypted with an individual key specific to an information sending device, and the individual key encrypted with a distribution key that is updated in a predetermined cycle, and supplied are sent to an information receiving device, and the information...http://www.google.com/patents/US8036388?utm_source=gb-gplus-sharePatent US8036388 - Information sending system, information sending device, information receiving device, information distribution system, information receiving system, information sending method, information receiving method, information distribution method, apparatus, sending method of information receiving device, playback method of apparatus, method of using contents and program storing medium
