Special Coverage: Blu-ray

Digital Rights Management

One goal of Blu-ray -- 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); like HD DVD, Blu-ray's DRM is based on the Advanced Access Content System (AACS), which uses a 128-bit key called the Advanced Encryption Standard. 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.

An additional, optional technology called BD+ allows content providers to respond to any attempts to hack AACS by reverse-engineering a legitimate player and trying to implement it in an unauthorized player or computer software. When that happens (and it is certain to happen at some point), BD+ allows the disc to detect that it is being played in a device containing known hacks and stop working. Once studios become aware that the DRM has been compromised, the security of a disc with BD+ can be temporarily renewed by the content supplier to continue providing protection. This remains completely transparent to users of legitimate devices.

To further deter unauthorized copying, Blu-ray also uses a physical key called ROM Mark. This technology is designed specifically to thwart large-scale, mass-production piracy, a problem that is estimated to cost the movie industry more than $3 billion per year in lost revenue. To combat this, ROM Mark embeds a unique identifier in pre-recorded BD-ROM media, such as movies, music, and games. Invisible to consumers, this ROM Mark can only be mastered with equipment available to licensed BD-ROM manufacturers, essentially preventing unauthorized copies of a disc.

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.

Another critical aspect of Blu-ray's DRM is called 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 AACS licensing agreement, which is expected to be in place by the end of this year. Under the current interim licensing agreement, managed copy is not required.

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