Patent ID: 7715558
Filing Date: 2010-05-11
Classification: G11B

Abstract:
1. A playback terminal for playing back content, the playback terminal comprising: a holding unit operable to hold device unique information pre-stored in the playback terminal, the device unique information being unique to the playback terminal; a content read unit operable to read encrypted content from a portable medium, the encrypted content being generated by encrypting content using at least medium information including an encrypted medium key, generated by encrypting a medium key with the device unique information, pre-recorded on the portable medium; a decryption method judgment unit operable to judge whether or not rights information including usage rights for the encrypted content managed by an external license server is required for decrypting the encrypted content; a medium information read unit operable to read the medium information pre-recorded on the portable medium; a communication unit operable to acquire the rights information managed by the external license server when it is judged that the rights information is required, the rights information managed by the external license server being a part of information which is required for the decryption of the encrypted content; a medium content key calculation unit operable to decrypt the encrypted medium key, with use of the device unique information, so as to obtain the medium key, and to cryptographically calculate a medium content key using the medium key; a license content key calculation unit operable to cryptographically calculate a license content key using the medium content key and the rights information acquired from the external license server; and a decryption unit operable to (a) decrypt the encrypted content using the medium content key, when it is judged that the rights information is not required, and (b) decrypt the encrypted content using the license content key, when it is judged that the rights information is required, wherein the decryption unit includes: a content key obtaining sub-unit operable to, when it is judged that the rights information is not required, obtain the medium content key used in decrypting of the encrypted content; and a content decryption sub-unit operable to, when it is judged that the rights information is not required, decrypt the encrypted content using the medium content key, the medium content key calculation unit, when it is judged that the rights information is not required, obtains the medium key by decrypting the encrypted medium key using the device unique information, the encrypted medium key recorded on the portable medium is generated by encrypting the medium key using device information of valid playback terminals, and the content key obtaining sub-unit fails to obtain the medium key by decrypting the encrypted medium key, when the device unique information of the playback terminal itself is not included in the device information of the valid playback terminals.