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Thursday, January 11, 2007

AACS: Will it work, or will it break?

I recently wrote a little about the copy-protection technologies being deployed in Windows Vista in reaction to a certain paper being published. The commentary that resulted made me realize that we need to demystify some things before we go further.

To condense a rather large and far-reaching technical mess into a more digestible tidbit, here are three major "pieces" to the next generation HD content playback system that will sit in your living room.

  1. Video output and display. The datastream between your multimedia player's video-out and your shiny HD behemoth screen is protected by a protocol called HDCP, which is spec'd to be layered on top of a connection such as HDMI.
  2. Multimedia Player. This is the device that handles all of the processing and number-crunching to change the stream of bits coming off your piece of media into a bright and happy A/V stream to throw at your display by means of Item #1. This is your set-top box or your home-theater PC's software player. This is the piece that Peter Gutmann's paper discusses in the context of Vista.
  3. Media Reader Device. This is the drive that spins that little shiny disc around, and shines pretty lasers at it, and decrypts that mess of noise into happy bits that Item #2 can understand. This is where we largely start talking about AACS (the very beefy replacement to CSS that protects HD-DVD and BluRay media).
Yes, there is a lot of crossover and gray area here. Each noodle in this acronym soup has varying degrees of impact and influence across all three of the above generalizations. But these generalized distinctions are important ones to make, and provide a necessary context for the discussion below.

A couple of guys at Freedom to Tinker are in the middle of a very interesting series of posts that talk about AACS in response to emerging reports that the system has been cracked.

Commentary has been all over the map, with some calling this a non-event and others seeing the death of AACS. Alex Halderman and I have been thinking about this question, and we believe the right view is that the software isn’t a big deal by itself, but it is the first step in the meltdown of AACS. We’ll explain why in a series of blog posts over the next several days.

Start with their first post, and work your way forward. It's a good, candid and interesting read.


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