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Making and Breaking HDCP Handshakes

Posted by ryuzaki0 on from the only-a-matter-of-time dept.

Cadre writes "Ed Felten describes the handshaking routine used by HDCP and how if any 40 devices conspire together, they can break the security of the system."

8 of 144 comments (clear)

  1. Re:Where did you get 40? by Anonymous Coward · · Score: 2, Informative
    From TFA:

    In the real system, where the secret vectors have forty entries, not four, it takes a conspiracy of about forty devices, with known private vectors, to break HDCP completely. But that is eminently doable, and it's only a matter of time before someone does it. I'll talk next time about the implications of that fact.

     
    Four was an example for the article.
  2. 'Old' news by bas.westerbaan · · Score: 5, Informative

    HDCP has been broken, and has been proved to be weak in 2001 twice. See http://apache.dataloss.nl/~fred/www.nunce.org/hdcp /hdcp111901.htm

  3. No, it's 40, not 4 by Space+cowboy · · Score: 4, Informative

    In real life the devices have a vector of 40 secret numbers, he's using a vector of 4 to illustrate withour bogging down the reader.

    The key is that with N variables (the number of different numbers in the vector), you need N equations to solve the set of equations for all of those variables - it's simple linear algebra.

    When you purchase a licence, you get a bunch of 10000 keys for $16000, so S.O.Mebody could use this within an organisation to analyse the generation matrix, and actually produce 40 new keys and release them to the wild. No comeback.

    Simon

    --
    Physicists get Hadrons!
  4. Re:A little tougher than that... by Maljin+Jolt · · Score: 4, Informative

    Anyone want to run a simulation?

    No funny simulation is needed, a math paper refered by TFA contains the info you want: 50 KSV's have probability 0.999, by the properties of linear algebra over Z/2exp56Z.

    --
    There you are, staring at me again.
  5. Re:Cool, but nor practical by Anonymous Coward · · Score: 1, Informative

    You don't need a license to obtain the secret keys. You can create your own thus making the approach extremely doable. Please read the article to see how this is done.

  6. Re:In a related question... by nsayer · · Score: 4, Informative

    1. There are HDMI to DVI cables. The only question mark is the type of DVI your card uses. There are 3 types, depending on which sets of signals the jack has: DVI-A, DVI-D and DVI-I. HDMI is all digital, but its backwards compatible with DVI-D (DVI-I is a combination of both A and D - analog and digital). So unless your card is DVI-A, you should be able to use a DVI-to-HDMI cable to hook up your display. You will need to make separate arrangements for audio, however, since DVI (unlike HDMI) has no provisions for it.

    This does presume that the card is able to put out a mode/timing that's compatible with the set, of course.

    2. What you're probably talking about is the requirement that non HDCP-hardened outputs from HD players are supposed to be down-resed to 480p (or whatever). I don't know for certain, but I'm willing to bet that this is not an absolute requirement, but that there's a bit that the disk can set to require this behavior. Not all studios or titles will make the decision to flip that bit on on their content, and I'd certainly expect them not to bother until/unless the technology to take DVI-B and rip it to MPEG4 becomes widespread. Unlike macrovision on analog outputs, which largely went unnoticed with DVDs, this bit does threaten to have a real impact on folks, so I would expect a site to pop up relatively shortly with a list of disks "not to buy" unless you have HDCP. The industry might even respond with a standardized icon on the box whose meaning is "HDCP required for full resolution."

    The other obvious restriction is that the HD media is itself encrypted, so when HD-DVD-ROM drives come out, you won't be able to read the data off of them (except in the context of an HD-DVD movie player app), at least not until it's reverse engineered and cracked like DVDs were.

    3. I may be wrong, but I am unaware of any HD video capture cards. There are HD tuner cards/boxes out there that will do HDTV, but they're decoding the RF from a TV station and getting MPEG2 streams. That's not the same thing as ripping 1080i from a DVI connector and turning THAT into MPEG2. Even if that were possible, the original source (HDTV, HD-DVD, DVD, whatever) was probably compressed in the first place, so you'll be recompressing it, which will degrade the picture some (more).

  7. Re:Cool, but nor practical by quentin_quayle · · Score: 5, Informative

    Did the moderators Read The Fine Article before giving the parent points?

    Felten in talking about "a conspiracy of about forty devices" is not saying that (defectors at) forty device makers have to reveal secret keys. What he's saying is that you just need to the 40 devices themselves, or rather (as post above pointed out) enough to get 40 different key sets (and some math and programming ability). Then the crack is done by analysing the bit streams between the devices (between player and display, or whatevre).

    The expense is the cost of all those tvs and players. Bribing the device makers is a *different* kind of attack which Felten rules out as impractical.

  8. Re:One thing I hate worse ... by Anonymous Coward · · Score: 1, Informative

    You don't need to hack the firmware on your dvd drive on a pc to enjoy region-free status. Just use mplayer or vlc or similar. They do the CSS-decoding in software and will play any region just fine, even if your drive has already become "locked" into one region.

    But, yeah - region encoding is a damn stupid idea :)