Content use management system, content playback apparatus, content use management method, content playback method, and computer program including system date/time information validation

摘要

A license corresponding to digital content includes reliable reference date/time information. A content playback apparatus includes a reference-date/time-information storage unit for storing the reference date/time information. The reference-date/time-information storage unit is updated to maintain the reference date/time information at the latest version. When the digital content is to be played back, the system date/time of the content playback apparatus is compared with the reference date/time to validate the system date/time.