An information recording/playback device stores beforehand, on a recording medium, secret information in which a writing/reading method thereof cannot be analyzed and which can be read only by a special reading method. The secret information is applied to a key for content encryption or decryption when...http://www.google.de/patents/US8127148?utm_source=gb-gplus-sharePatent US8127148 - Information recording device, information playback device, information recording method, information playback method, and information recording medium and program providing medium used therewith
