Patent ID: 7698571

Claim:
A digital work protection system for recording and playing back digital works, comprising: a portable recording medium device including a storage area; and a record/playback device being usable under a contract between a user and a service provider, the record/playback device including: an internal storage unit that stores a content that is a digital work; a unique information storage unit that prestores device unique information to generate encrypted information, the device unique information indicating the record/playback device and being protected from being written over with an external device of the record/playback device; an encryption unit that, when the stored content is written from the internal storage unit to the portable recording medium device, encrypts the stored content based on the prestored device unique information to generate encrypted information; a write unit that writes the generated encrypted information into the storage area of the portable recording medium device; a read unit operable to read the encrypted information from the storage area of the portable recording medium device; a decryption unit that decrypts the read encrypted information based on the prestored device unique information stored in the unique information storage unit to generate a decrypted content; a playback unit that plays back the generated decrypted content; wherein the encrypted information is neither decrypted nor played back by any device other than the record/playback device generating the encrypted information, wherein a model change device replaces the record/playback device with another record/playback device due to a change in the contract between the user and the service provider, the device unique information stored in the unique information storage unit is read, the device unique information is deleted from the unique information storage unit and the read device unique information is written into the other record/playback device.