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This is Leo Notenboom for

This week the tech and geekier news outlets were all abuzz about a number, and how that number was being posted in literally thousands of places around the internet in defiance of those wanting to keep that number secret.

By the end of the week that number was appearing on stickers, in photos, in music (mp3) and has even become someone's tattoo.

So what's so special about this number?

It's the decryption key for all high definition DVDs produced to date.

It's not a copyright issue (or if it is, that's beside the point), but the AACS, who own and control the DVD copy-protection scheme is apparently sending out DMCA take-down notices as fast as they can print them. (AACS stands for Advanced Access Content Systems, and DMCA is the Digital Millennium Copyright Act which attempts to codify the relationship of copyright to easily copied digital media.) Even though this isn't a copyright issue per se, the DMCA also covers issues such as possession of technology which could be employed to break the encryption used by copyright holders.

In other words being in possession of this number could be a crime.

To grossly oversimplify since the actual methods are incredibly complex, the technical issue is simply this: using public key encryption, the private "secret" key that's required to unlock the encrypted digital information must be kept in every device capable of using that media. So your HD-DVD player has the key. It's well hidden, but it's there.

If your computer can play HD-DVD, that key is there too. Hidden in the software, but it's there.

And the number? It's that key. It's a 128bit number that, with the right software, can be used to decode HD-DVDs and render the copy protection scheme pointless.

Yes, the key's already been changed, but given that this key was found I don't doubt that the next key will be too. And the key after that. And after that.

Given the incredibly complex software and infrastructure that needed to be created to support this scheme, and that it's really only going to keep honest people honest since hackers will naturally step up to the challenge and crack it, and make those cracks available to the less-than-honest anyway...

Someone remind me ... why are we doing this again?

I'd love to hear what you think. Visit and enter 11463 in the go to article number box to access the show notes and to leave me a comment. While you're there, browse over 1,100 technical questions and answers on the site.

Till next time, I'm Leo Notenboom, for

Article C3014 - May 5, 2007 « »

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Leo Leo A. Notenboom has been playing with computers since he was required to take a programming class in 1976. An 18 year career as a programmer at Microsoft soon followed. After "retiring" in 2001, Leo started Ask Leo! in 2003 as a place for answers to common computer and technical questions. More about Leo.

Not what you needed?

dave b
May 5, 2007 8:46 PM

Reminds me of the old floppy days when the manufacturers would use a laser to permanently damage the disk as a "signature." The software would look for this "signature" when starting - if the damaged area was missing (i.e., the software had been copied to an error free disk) the software would not run. It took no time for programs like CopyWrite to be created to circumvent these schemes. Some companies required that "master" floppies be locked up - so they used CopyWrite to create back-up floppies that would run on the user's machine. Cost, circumvention, and user outrage eventually eliminated the laser burned floppies from existence.

May 7, 2007 8:15 AM

So, the key has been changed. What does that mean to everyone who already owns an HD-DVD player? Does it mean they can only play "old" HD-DVD movies, or that they'll need to be brought in to get (and pay for?) an "upgrade" to the new key? (Actually, they'll need both keys. And then all three keys once the second is broken. And then all four. And so on.)

Leo A. Notenboom
May 7, 2007 11:02 AM

Hash: SHA1

It's unclear, but recall that I said the mechanism was extremely complex. :-) I
believe there's a way for most players to continue playing new DVDs. Just how they
pull that off, I'm not sure.
Version: GnuPG v1.4.6 (MingW32)


May 11, 2007 11:32 AM

I think that everything will be how it always has. Copy protection devices and security measures will fail as hackers and reverse engineers will always be able to figure it out. That's just the way it is. No software, no DVD, CD, or any media that you are trying to protect would be safe. This has gone on for YEARS and will also go on. Its a battle where no one can win. There will always be people trying to come up with a copy protection that CANT be broken, and there will always be people who HAVE/CAN break it. Thats what I think about this subject.

John Ellerington
May 14, 2007 2:38 AM

Copy protection is a waste of time and effort. At some point, all digital media has to be converted to an analogue form in order to view / listen to it, and at that point it can be re-recorded; OK, so there is some loss of quality, but I guess most people who are prepared to buy pirated media will accept that as a trade off against the low price they pay. The media companies need to cut their prices drastically so that piracy ceases to be economically viable - it's as simple as that.

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