Patent ID: 8448259

Claim:
A content playback device, comprising: a playback unit configured to play back a content; a normal storage unit that is not tamper-resistant; a secure storage unit that is tamper-resistant; a first control unit configured to write playback records into the normal storage unit one by one at regular time intervals, each playback record indicating elapsed playback time of the content; and a second control unit configured to (i) write monitoring records with respect to the playback records into the secure storage unit one by one at randomly-generated time intervals and (ii) determine that the playback records have not been tampered with if a prescribed relation is satisfied between a specific time point obtained according to a latest one of the monitoring records and one of the playback records corresponding to the specific time point; wherein the prescribed relationship is satisfied when either: the specific time point matches the elapsed playback time indicated by the corresponding playback record; or the specific time point is less than the elapsed playback time indicated by the corresponding playback record.