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| Sep 24, 2008 - About DVD COPY Protection - 07. |
High-Bandwidth Digital Content Protection (HDCP, DVI, and HDMI)
HDCP is similar to DTCP, but it was designed for digital video monitor interfaces. In 1998, the Digital Display Working Group (DDWG) was formed to create a universal interface standard between computers and displays to replace the analog VGA connection standard. The resulting Digital Visual Interface (DVI) specification, released in April 1999, was based on Silicon Image's PanelLink technology, which at 4.95 Gbps can support 1600×1200 (UXGA) resolution, which covers all the HDTV resolutions. Intel proposed HDCP as a security component for DVI. A new connection standard called HDMI combines DVI and HDCP. DVD players with DVI or HDMI digital video output appeared in spring 2003. Many new HDTV displays are likely to have both IEEE 1394 and HDMI connections.
HDCP provides authentication, encryption, and revocation. Specialized circuitry in the playback device and in the display monitor encrypts video data before it is sent over the link. When an HDMI output senses that the connected monitor does not support HDCP, it lowers the image quality of protected content. The HDCP key exchange process verifies that a receiving device is authorized to display or record video. It uses an array of forty 56-bit secret device keys and a 40-bit key selection vector -- all supplied by the HDCP licensing entity. If the security of a display device is compromised, its key selection vector is placed on the revocation list. The host device has the responsibility of maintaining the revocation list, which is updated by system renewability messages (SRMs) carried by newer devices and by video content. Once the authority of the receiving device has been established, the video is encrypted by an exclusive-or operation with a stream cipher generated from keys exchanged during the authentication process. If a display device with no decryption ability attempts to display encrypted content, it appears as random noise.
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