April 23, 2024

HD-DVD Requires Digital Imprimatur

Last week I wrote about the antitrust issues raised by the use of encryption to “protect” content. Here’s a concrete example.

HD-DVD, one of the two candidates for the next-gen DVD format, uses a “content protection” technology called AACS. And AACS, it turns out, requires a digital imprimatur on any content before it can be published.

(The imprimatur – the term is Latin for “let it be printed” – was an early technology of censorship. The original imprimatur was a stamp of approval granted by a Catholic bishop to certify that a work was free from doctrinal or moral error. In some times and places, it was illegal to print a work that didn’t have an imprimatur. Today, the term refers to any system in which a central entity must approve works before they can be published.)

The technical details are in the AACS Pre-recorded Video Book Specification. The digital imprimatur is called a “content certificate” (see p. 5 for overview), and is created “at a secure facility operated by [the AACS organization]” (p. 8 ). It is forbidden to publish any work without an imprimatur, and player devices are forbidden to play any work that lacks an imprimatur.

Like the original imprimatur, the AACS one can be revoked retroactively. AACS calls this “content revocation”. Every disc that is manufactured is required to carry an up-to-date list of revoked works. Player devices are required to keep track of which works have been revoked, and to refuse to play revoked works.

The AACS documents avoid giving a rationale for this feature. The closest they come to a rationale is a statement that the system was designed so that “[c]ompliant players can authenticate that content came from an authorized, licensed replicator” (p. 1). But the system as described does not seem designed for that goal – if it were, the disc would be signed (and the signature possibly revoked) by the replicator, not by the central AACS organization. Also, the actual design replaces “can authenticate” by “must authenticate, and must refuse to play if authentication fails”.

The goal of HD-DVD is to become the dominant format for release of movies. If this happens, the HD-DVD/AACS imprimatur will be ripe for anticompetitive abuses. Who will decide when the imprimatur will be used, and how? Apparently it will be the AACS organization. We don’t know how that organization is run, but we know that its founding members are Disney, IBM, Intel, Microsoft, Panasonic, Sony, Toshiba, and Warner Brothers. A briefing on the AACS site explains the “AACS Structure” by listing the founders.

I hope the antitrust authorities are watching this very closely. I hope, too, that consumers are watching and will vote with their dollars against this kind of system.


  1. Note that the spec pointed to is for “Prerecorded Video”, so the fears about not being able to have consumer-made disks may be unnecessary.nice blog thnxxx

  2. A HD DVD Guy says

    AACS is optional in the HD DVD format. It is required in Blu-ray. When preparing the HD DVD specifications, the DVD Forum insisted that AACS be optional for concerns not unlike those raised here and also the costs associated with licensing and using AACS. Therefore much of the arguments made here are not applicable to HD DVD. But they ARE applicable to Blu-ray.

    Blu-ray is a draconian system that is three times more expensive to author with and costs four times more per disc to manufacture. Because of this and the AACS/BD+ requirements, if Blu-ray wins the format war, it will never be the success story that DVD has become. DVD has wide support because it is cheep and because it has the right required features and the right optional features. HD DVD was modeled on the DVD system. Blu-ray is simply not a consumer system. It is fundamentally flawed from a feature set and studio economic standpoint and this AACS related discussion is just one of many examples….

    If you want to have some lively anti-trust discussion, take a look at why an independent studio selects HD DVD over Blu-ray and why Fox, Disney and MGM are exclusive to Blu-ray when the cost of their goods is so much more expensive and technically inferior to HD DVD. Blu-ray is restraining trade by locking these companies into one format and exdending disc manufacturing price protection to them as long as they are exclusive to Blu-ray and make discs at Sony’s DADC facility. Their predatory and unfair pricing is hurting the disc manufactures by taking their business. If HD DVD loses, Sony is going return it’s price to a fair market amount and further hurt Hollywood and the consumers.

  3. Note that the spec pointed to is for “Prerecorded Video”, so the fears about not being able to have consumer-made disks may be unnecessary.nice blog thnxxx

  4. useful blog thanks blogger

  5. So, how long will it be before hacked versions of HD movies tell your player to revoke all your legitimately playable movies? The serious pirates will be able to produce their own illegal copies using forged or repurposed imprimaturs, but the sheer hack value of preventing legitmate movies from playing will be irresistable.

    Let’s face it, DRM technology is at best problematic. What is that new Microsoft/Intel hardware we keep hearing about except a mechanism for keeping you from deleting viruses and spambots? The real pirates will get and sell copied stuff just fine, but just try and get back in control of your own computer.

  6. James Donahue says

    This is going to hurt more than help.

    As we see, it will infringe on fair-use rights, and more. If they put that AAC chip in, we won’t be able to use our family movies in there. Bah. I took a video of my 3-year-old neice playing tag in the back yard. It played nice in my DVD player. Then, I went out to get the HD-DVD player. Guess what, that 3-year-old video won’t play in my HD-DVD player. I mean WHAT!? If I can’t record my family videos and put that on the HD-DVD player, than what is this? If they want to do put this **bleep** crap in the HD-DVD player, you are going to tick people off. Does this mean that digital cameras and digital camcorders are going to become illegal? It’s time to write to congress NOW, and give back our fair-use rights.

    There are OTHER ways to secure media than putting that anti-copy crap in this. Why not put DRM in the player, so that we can copy our movies, but it won’t play in another person’s player, while it will play in ours. They need to respect our fair use rights.

    I hope for goodness’ sakes that our next presidental campain will bring this copyright reform up so that we can maintain our culture and not have to deal with the crap they are slapping out to our families. I hope that they will outlaw lenghy unskippable commercials when it comes to movies.

    And I have one more thing to say. Welcome to China. 🙁

  7. Wes Felter says

    DMCA, patents, and trade secrets are defense in depth, of course.

    Supposedly HD-DVD and Blu-ray have contractual financial incentives (i.e. massive liability) to encourage the player vendors to really be tamperproof this time. I guess we’ll see.

  8. Alexander Wehr. says

    If the patent or trade secret possibilities were true, then why did they lobby for the DMCA?…

    xbox was also supposed to be tamper proof.. but a few different people figured out how to flash the console’s bios without need of any hardware based mods.

  9. Wes Felter says

    If they can’t get you on DMCA, they’ll get you on patent or trade secret. Or post-Grokster “inducement”.

    Besides, all the players are supposed to be tamperproof.

  10. Alexander Wehr. says

    I have a very pertinent quesiton on this.

    wouldn’t it be perfectly and completely legal to market a tool to remove this particular restriction in these players?

    It is not an “access control” embedded in the copyrighted work. Nor is it a rights control. It definitely exceeds the defined boundaries of “technical proteciton measures”.

    Or perhaps you could explain how such a suit would work?

  11. Bob Jonkman says

    (Comments no longer allow hyperlinks?)

    John Walker’s Digital Imprimatur paper is at http://fourmilab.ch/documents/digital-imprimatur/

  12. Bob Jonkman says

    Two years ago John Walker wrote a paper called “The Digital Imprimatur“. It addresses many of the questions asked in previous comments.


  13. Well, as Dr. Felten hinted, if there is any way for consumers to make their own unprotected HD-DVDs, then what’s to stop you from putting a movie onto your consumer HD-DVD? Voilà, instant independent or bootleg HD-DVD. Having a system to pre-approve the discs that can be played is only useful if it applies to every single disc; if some discs don’t need an imprimatur, then, essentially, no discs need an imprimatur. Unless of course the imprimatur-less consumer-made discs are crippled in some way (inferior video quality etc.), which I’m sure consumers will love.

    Granted, the protection may make it difficult for people to get the movie off of the original disc, but that’s hardly going to stop copies from becoming available online, through the analog hole if nothing else.

    IMO the whole thing is rather pointless for preventing bootlegging because DVD quality is more than good enough for the vast majority of people who would be interested in getting illegal copies of movies, and I don’t see DVD playback capability going away anytime soon, so bootleggers will just continue to use the DVD format. It seems like this would have the most effect on independent movie producers, who would be unable to compete with the large studios on video quality. I’m betting this is intentional.

  14. Wes Felter says

    Is it possible for an HD-DVD disc to not use AACS at all? In which case, the imprimatur would not come into play.

    Besides revocation, isn’t this the same situation as CSS DVDs? In order to manufacture CSS-protected DVDs you need a (very restrictive) license from DVD CCA.

    Also, HD-DVD-R exists and I can’t believe that it simply doesn’t work.

  15. Scott,

    I doubt they will allow consumers to record any desired content on discs that are compatible with these. If they did, there would be no point in having the imprimatur mechanism.

    There is another specification for Recordable Video, but it is all about controlling time-shifting and other recording and transfer of copy-controlled works.

  16. Ned Ulbricht says

    Licensing Act, 1662

    An Act for Preventing the Frequent Abuses in Printing Seditious Treasonable and Unlicensed Books and Pamphlets and for Regulating Printing and Printing Presses
    14 Chas. 2, c. 33 , 1662

    Whereas the well-government and regulating of Printers and Printing Presses is matter of Publique care and of great concernment especially considering that by the general licentiousnes of the late times many evil disposed persons have been encouraged to print and sell heretical schismatical blasphemous seditious and treasonable Bookes Pamphlets and Papers and still doe continue such theire unlawfull and exorbitant practice to the high dishonour of Almighty God the endangering the peace of these Kingdomes and raising a disaffection to His most Excellent Majesty and His Government For prevention whereof no surer meanes can be advised then by reducing and limiting the number of Printing Presses and by ordering and setling the said Art or Mystery of Printing by Act of Parliament in manner as herein after is expressed. The Kings most Excellent Majesty by and with the Consent and Advise of the Lords Spiritual and Temporal & Commons in this present Parliament assembled doth therefore ordaine and enact ….

  17. Randy Picker says

    If you are interested, I discuss some of the antitrust issues associated with DVDs in a new post. See http://picker.typepad.com/picker_mobblog/2005/07/picker_dvds_and.html

  18. Scott Preece says

    Note that the spec pointed to is for “Prerecorded Video”, so the fears about not being able to have consumer-made disks may be unnecessary. It could be that this spec is intended to apply only to disks whose creators want to rely on this mechanism.

  19. “I don’t think they’ll revoke a disc just because some unauthorized exact copies of it have been released.”

    I think Anonymous meant “what happens when someone works out how to fake the revocation?” Or worse yet, what if the movie studios start playing nasty games, deliberately placing dirty copies of movies on P2P networks? You download the copy, play it, and all of a sudden your player won’t play *anything* as the copy revoked the whole lot in a sort of “serves you right for downloading movies” move…

  20. Anonymous,

    I don’t think they’ll revoke a disc just because some unauthorized exact copies of it have been released. As you say, that would cause huge disruption for law-abiding consumers.

    If “this gets hacked” means that a blackhat can create arbitrary discs with valid signatures, then it’s game over anyway.

  21. Anonymous says

    So, what happens when this gets hacked? Joe Blackhat releases a pirate HD-DVD of the latest blockbuster, lots of people download, then return their HD-DVD players to walmart because “It won’t play my kids Disney films” (the disc deauthorised every disney release the blackhat could google). I can’t see the retailers being very happy with that.

  22. And all this also means that amateur film-makers won’t be able to distribute their own material on HD-DVD and you won’t be able to send Auntie Doris film of her grand-kids without permission from some clowns somewhere; presumably the imprimatur will have some sort of dollar value attatched?

    Still, I give it 5 minutes before DVD Jon does his magic and the whole thing becomes moot…

  23. I see the closed system as the problem — the fact that (whoever controls) AACS-LA controls access to a major channel for distributing video content. Revocation makes the problem worse, since it gives AACS-LA leverage even over content that it has already approved for distribution.

  24. Randy Picker says

    I want to make sure that I understand your focus. Is it the closed system or the uncertainties of the revocation prodedure? By closed system, I mean that the platform creator controls who can access the platform with new content and does so through the imprimatur.

  25. My understanding is that in some times and places, it was actually illegal to publish a book that lacked an imprimatur. I edited the sentence you quoted, to be more precise.

    The original Catholic imprimatur still exists, but plays only an advisory role.

  26. “Works could not be printed without an imprimatur.”

    I’m pretty sure this was never the case. The procedure is this.
    A Catholic who writes a work on religious matters would normally (at least
    in the past, I’m not sure about today) submit his work to his diocese.
    The book would be examined by a diocesan official (who may well have
    been/still is called a “Censor”), and should it contain nothing contrary
    to Catholic teaching, be given a “Nihil Obstat” (lit. nothing stands in
    the way; no objection). A book with a Nihil Obstat would then be passed
    to the bishop of the diocese himself, who, if he also found nothing wrong
    with it, would give it his “Imprimatur” (let it be printed).

    Basically, all both terms certify is that the book is free of doctrinal
    or moral error.