Special Coverage: HD DVD

Digital Rights Management

One goal of HD DVD -- and a stringent requirement from the movie studios -- is to make unauthorized duplication as difficult as possible. This is generically known as digital rights management (DRM); HD DVD's DRM is based on the Advanced Access Content System (AACS), which uses a 128-bit key called the Advanced Encryption Standard (AES). Each player (not each model, but each individual unit) includes a unique key, and other unique keys are assigned to the content. These keys are "revocable and renewable" -- if the encryption is hacked, they can be changed at the mastering stage.

Perhaps the most famous -- or infamous -- element of AACS is the Image Constraint Token (ICT), which content providers can use to limit the resolution of the analog component output to 540p at most, though most players will likely do 480p. This prevents anyone from recording high-def content from the otherwise unprotected analog output, but it also disenfranchises anyone with an HDTV that has a DVI input without HDCP copy protection or no DVI/ HDMI input at all.

Fortunately, most studios have announced that they will not implement ICT, at least for now. If piracy becomes rampant, they could throw that switch on future titles. However, I suspect they won't; according to Knox, the most prevalent form of piracy today is camcorders in theaters, not unauthorized duplication of DVDs, because movies are most valuable before they are released on disc. Also, competition among the studios is likely to prevent any of them from being the first to activate ICT.

Another critical aspect of HD DVD's DRM is called mandatory managed copy, which allows consumers to make authorized copies of discs they buy for their personal use. This could include copying the content to a media server or portable player or burning a backup copy. The process need not be free of charge, and content providers could require consumers to enter into an online transaction of some sort to allow the copy.

Every disc will be required to offer some form of managed copy under the final licensing agreement.. Under the current interim licensing agreement, managed copy is not required; in fact, even if it is included on the disc, it cannot be "turned on" until the final agreement is in place. It is unknown how this will affect the early adopters who buy the first discs, though it is theoretically possible to add the managed-copy transaction for these discs if the content provider included that option.

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