COPYRIGHT PROTECTION SYSTEM, ENCIPHERING DEVICE, DECODING DEVICE AND RECORDING MEDIUM

摘要

PROBLEM TO BE SOLVED: To provide a system for preventing illegal decoding of digital contents which are recorded on a recording medium and have decoding limit. SOLUTION: In a communication system consisting of an enciphering device and a decoding device which share a contents key perform cipher communication by using the contents key, the enciphering device and the decoding device mutually authenticate that the opposite devices are a legitimate device with mutual authentication and also share a time varying key form a random number used for the mutual authentication. The decoding limit such as the number of reproducing times data stored in the decoding device is enciphered with the time varying key, transferred to the decoding device while security is conducted, also updated by both devices and the decoding limit is shared. In the case of loading contents, the cipher communication is performed by using a contents key generated from the updated decoding limitation.