Chapter 1

General DVD 25
High-Bandwidth Digital Content Protection (HDCP) and HDMI
High-Bandwidth Digital Content Protection (HDCP) is similar to DTCP, but it
has been designed for digital video monitor interfaces such as digital visual
interface (DVI). 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 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,
covering all the HDTV resolutions. Intel proposed a security
component for DVI: HDCP. A new connection standard called HDMI now
combines DVI and HDCP, and 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 40 56bit
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 (XOR) operation with a stream cipher
generated from keys exchanged during the authentication process. If a display
device with no decryption capability attempts to display encrypted
content, it appears as random noise.
The first four forms of copy protection are optional for disc producers.
Movie decryption is also optional for hardware and software playback
manufacturers: A player or computer without decryption capabilities will
only be able to play unencrypted movies. CPRM is handled automatically
by DVD recorders, whereas DCPS and HDCP are performed by the DVD
player, not by the disc developer.
These copy protection schemes are designed only to guard against
casual copying (which the studios claim causes billions of dollars in lost revenue).
The goal is to “keep the honest people honest.” The people who
developed the copy protection standards are the first to admit they can’t
stop well-equipped pirates.
Movie studios have promoted legislation making it illegal to defeat DVD
copy protection. The result is the World Intellectual Property Organization