| 摘要 |
<p>A copyright protection system for protecting content wherein a time dependent ticket is calculated (314) at a source device (330) by combining a checkpoint with a ticket. The checkpoint is transmitted (361) from a display device (340) to the source device prior to the source device transmitting (360) watermarked content to the display device. The checkpoint is also stored (376) at the display device. Thereafter, the source device transmits, to the display device, watermarked content, the ticket, and the time dependent ticket. At the display device, the stored checkpoint is compared (314) to a current count of a local clock (374) that was utilized for producing the checkpoint. If the stored checkpoint is within a window of time of the local clock, then the stored checkpoint is combined (314') with the ticket in the same way that the checkpoint is combined with the ticket at the source device. A result of the combination is compared to the time dependent ticket and if the result equals the time dependent ticket, then the watermark and ticket may be compared in the usual way to determine the copy protection status of the copy protected content (314').</p> |
