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December 30, 2006

AACS cracking - here's the deal

Please note, this blog has been archived and now lives at www.discretecosine.com

Earlier this week, news broke that someone had "cracked" the AACS DRM system used by both HD-DVD and BluRay. At this point, there hasn't been independent verification of any of this, but here's the deal as best as I understand.

A guy named muslix64 on the Doom9 forums figured out a way to extract title keys from HD-DVD discs, very likely using a vulnerability in Power DVD 6.5. He then wrote a decryption tool based on the publicly available AACS specifications. He released the software, including source, but did not release any title keys. He made hints that there is a fundamental flaw in the way title keys are handled, and that player revocation is unimportant. With player revocation, a flawed player (such as Power DVD, if indeed it is vulnerable) can be disabled from playing future discs.

It's interesting, if indeed it's true. There is no evidence that the AACS encryption itself is flawed, and indeed, that seems unlikely as it's essentially an implementation of AES. However, we know that using encryption for DRM on untrusted hardware is likely to have some vulnerability, if you're willing to dig deep enough. That is apparently what's happened here.

What does it mean? Not much right now. Muslix64 has disappeared, and nobody has been able to discover the relevant title keys at this point. If someone does recreate a title key extraction method, it would be an interesting alternative to the world of DVD cracking. Instead of having a DMCA-violating circumvention device in the form of DeCSS or any of the later decryption programs, you could instead have a totally legitimate decoder tool paired with some title keys. The legality of the title keys would be questionable - the court case would be very interesting. In any case, it's likely that you'd get your HD-DVD, check online to get the title key, paste it into your ripper and be done.

Give it 6 weeks and check again. This could be a blip, this could be the death of BluRay and HD-DVD. We'll see.

Posted by at December 30, 2006 6:44 PM | News | Opinions

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