Patent ID: 7555129
Filing Date: 2009-06-30
Classification: G06F,G11B

Abstract:
1. A content playback apparatus comprising: a key storage unit operable to store a device key pre-assigned to said content playback apparatus; an information reading unit operable to read, from a recording medium having a pre-assigned media key and pre-storing main content, (i) key management information obtained by encrypting, based on the device key, one of (a) the media key and (b) a piece of revocation information, the piece of revocation information indicating that said content playback apparatus has been revoked, and (ii) the main content; a sub-content obtaining unit operable to obtain encrypted sub-content, the encrypted sub-content being data generated by encrypting sub-content based on a content key, the sub-content being content relating to the main content recorded on the recording medium, and the content key being a key generated by applying a predetermined operation to key generation information based on the media key; a key obtaining unit operable to decrypt, based on the device key, the key management information to obtain one of (a) the media key and (b) the piece of revocation information; an information obtaining unit operable to obtain key generation information from an information source other than the recording medium; a key generation unit operable to, when said key obtaining unit has obtained the media-key, apply a predetermined operation to the obtained key generation information to generate a content key, the predetermined operation being applied to the obtained key generation information based on the media key; a decryption unit operable to decrypt the encrypted sub-content based on the content key; and a playback unit operable to play the main content and the decrypted sub-content.