Gateway monitor marks premiere of display-based HD protection scheme

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Gateway monitor marks premiere of display-based HD protection scheme


Irvine (CA) – The introduction by Gateway of the FPD2185W 21″ high-resolution LCD to its product line brings to the computer display market some technologies that Gateway has featured in its widescreen, high-definition TV displays for the past few years. Among these is a controversial feature called High-bandwidth Digital Content Protection (HDCP).

Gateway’s language in introducing HDCP may leave customers with some intriguing questions, as it may raise more concerns than it resolves: “The 21″ Widescreen comes with built-in innovative compatibility features so you can handle tomorrow’s technology today,” begins one paragraph. “The HDCP Video Content Encryption Chip allows encrypted high-definition video to be played on the display through the DVI port. The Protection Video Path ensures the display is compatible with future software packages.”

Some will interpret “future software packages” to include Microsoft Windows Vista, which will support HDCP internally, Microsoft announced last April. Speculation arising from that announcement led to inaccurate reports today that Vista would require users to upgrade their monitors, and that Gateway’s would be among the first wave of “Vista-ready” replacement monitors. Vista will require HDCP monitors for playback of high-definition content; but if a high-def monitor is not installed, Vista will apparently comply with directives from HDCP’s licensing agent, Digital Content Protection LLC, mandating that quality of playback for high-def content be reduced for lower-resolution displays.

The basic concept of HDCP is fairly simple: Decades ago, VHS manufacturers implemented crude means to try to prevent two cassette decks from being linked together, enabling a consumer to make a direct copy from an original. Customers classically thwarted these schemes by placing a TV in-between the playback deck and the copy deck. The copy deck simply recorded whatever was output from the TV. The recording quality was somewhat degraded, but for customers of the late 1970s and early ’80s, that didn’t matter much.

More recently, content providers’ fears were that a similar scheme could be used to copy digital media from a digital TV, but without the loss of playback quality. So Intel spearheaded an initiative to endow these digital devices with digital networking equipment, which would include authentication and encryption. Using already proven network authentication protocols, HDCP devices would authenticate themselves to one another, in a kind of peer-to-peer handshaking scheme very similar to PGP. In this scheme, all the HDCP devices in a digital network broadcast initiation signals to one another, which are encrypted using their own private keys. Such messages can only be decrypted using these devices’ public keys, which in this scheme are essentially long serial numbers that are attached to these signals. Properly decrypted signals serve as proof that the devices are what they claim to be, since only they could have encrypted the signals using the unshared keys.

Once authentication is complete, the devices can then agree upon a protocol for the transmission of streaming signals, and the encryption of those signals along the way. Here, the protocol calls for the creation of what is called the HDCP cipher, which is essentially the equivalent of a PGP “session key,” except that all the connected devices play a role in the cipher’s generation. This cipher (key) is used to encrypt content between them; but in this protocol, after the passing of so many screen refresh periods known as “vertical blanking intervals,” the cipher is re-generated, and the stream becomes encrypted with an entirely new key. This way, even the breaking of one key would only result in the successful capture of a few seconds’ worth of the stream.

HDCP doesn’t lock out older monitors, but it does reduce picture quality

Some marketing literature has attempted to distinguish HDCP from copy protection schemes, perhaps to appease movie studios and content providers whom this technology directly addresses. Technically, studios can still apply their choice of copy protection schemes to the medium of choice – for high-definition discs of the future, whether Blu-ray or HD DVD, AACS will be the apparent copy protection method. But HDCP is a kind of copy protection scheme, but using network terminology, it “resides at the transport level.” In other words, it protects the transmission of content over cables (“digital video interfaces,” or DVI). The scheme is reportedly not flawless; the encryption scheme that is, however, has yet to be announced by anyone, anywhere.

In August of last year, the US Federal Communications Commission formally adopted HDCP. As a result, high-definition equipment approved for sale in the US must support this protocol; both HD DVD and Blu ray have already complied. Because Gateway’s monitor is as large as it is, and has a resolution high enough to support high-def video, it may have had to support HDCP by federal mandate – in other words, Gateway didn’t have a choice.

The HDCP technical protocol itself does not stipulate how devices are to function when connected digitally to non-compliant devices, or those that don’t speak the language. However, since its candidacy for adoption as an FCC protocol, its licensing body has drafted a document that mandates as a code of conduct, not a technical protocol, how manufacturers are to treat non-compliant devices, in circumstances where they’re used to view and perhaps record digital broadcasts. In a 2002 draft plainly entitled, “Requirements for the Protection of Unencrypted Digital Terrestrial Broadcast Content Against Unauthorized Redistribution,” the licensing body stipulates that compliant devices not pass “unscreened content” (not HDCP-encrypted) to a non-compliant device, unless it’s an analog TV – in which case, a copy made from that TV would have lesser reproduction quality – or, among other circumstances, the following:

…where such Covered Product is incorporated into a Computer Product and passes, or directs to be passed, such content to an unprotected DVI output as an image having the visual equivalent of no more than (a) 350,000 pixels per frame (e.g. an image with resolution of 720 x 480 pixels for a 4:3 (non-square pixel) aspect ratio) and (b) 30 frames per second. Such an image may be attained by reducing resolution, such as by discarding, dithering or averaging pixels to obtain the specified value, and can be displayed using video processing techniques such as line doubling or sharpening to improve the perceived quality of the image.

In other words, the requirements of conduct mandate that playback devices must intentionally blur their output when they know they’re connected to non-compliant or low-definition displays. This is how Vista gets around the problem of us continuing to use our old monitors: In order for Vista to comply, the HDCP devices that Vista supports – presumably through drivers – will intentionally reduce quality of output for older monitors. This way, any “daisy-chained” recording through those monitors will result in a lesser quality reproduction.

The April 2002 draft of this requirements document remains the latest one publicly available. What is curious about this particular draft is that it maintains a placeholder for a section that would, at some later time, specify just what a “Covered Product” should be. In other words, the current language doesn’t state which CE or PC components would comply, and which don’t. The placeholder language asks the reader to refer to “studio representatives to the drafting committee” – apparently a reference to technology representatives from major studios, who may have created such a list in the over three years since the document was drafted. However, the details of such a basic hardware requirements list, if it exists, are presently unknown, at least to the public.