July 14, 2024

CD DRM: Attacks on Disc Recognition

Ed and I are working on an academic paper, “Lessons from the Sony CD DRM Episode”, which will analyze several not-yet-discussed aspects of the XCP and MediaMax CD copy protection technologies, and will try to put the Sony CD episode in context and draw lessons for the future. We’ll post the complete paper here next Friday. Until then, we’ll post drafts of a few sections here. We have two reasons for this: we hope the postings will be interesting in themselves, and we hope your comments will help us improve the paper.

Today’s excerpt is from the middle of the paper, where we’re wading through details about the copy protection systems and the techniques they use to recognize protected CDs.

Please note that this is a draft and should not be formally quoted or cited. The final version of our entire paper will be posted here when it is ready.

Attacks on Disk Recognition

The active protection mechanisms introduced earlier selectively regulate access to raw CD audio, blocking access to the audio tracks on albums protected with a particular scheme while allowing access to all other titles. To accomplish this, the schemes install a background process that interposes itself between applications and the original CD driver. In MediaMax, this process is a kernel-mode driver called sbcphid.sys. XCP uses a pair of filter drivers attached to the CD-ROM and IDE devices called crater.sys and cor.sys. In both schemes, the active protection drivers examine each disc that is inserted into the computer to see whether access to it should be restricted. If the disc is recognized as copy protected, the drivers monitor for attempts to read the audio tracks, as would occur during a playback, rip, or disc copy operation, and corrupt the audio returned by the drive to degrade the listening experience. MediaMax introduces a large amount of random jitter, making the ripped audio sound like it has come from a badly scratched or damaged CD; XCP replaces the audio with random noise.

Each scheme’s active protection software interferes with attempts to rip or copy any disc that is protected by the same scheme, not merely the disc from which the software was installed. This requires some mechanism for identifying discs that are to be protected. This section discusses the security requirements for such a recognition system, describes the design and limitations of the actual recognition mechanism employed by the MediaMax scheme, and presents an improved design that better satisfies the requirements.

Recognition Requirements

Any disc recognition system must involve detecting some identifying feature on discs protected by a particular scheme. Ideally, such a feature would satisfy these requirements:

  1. Uniqueness. The feature should identify protected discs without accidentally triggering the copy protection on unprotected titles.
  2. Detectability. It should be possible for the active protection drivers running on client systems to reliably and quickly detect the feature in protected discs. In practice, this limits the amount of audio that can be read from the disc before deciding whether to apply protection.
  3. Indelibility. The feature should be difficult to remove without substantially degrading the quality of the audio; that is, it should be difficult to make a copy of the copy protected disc that does not itself trigger the protection.
  4. Unforgeability. It should be difficult to apply the feature to an unprotected album without the cooperation of the protection vendor, even if the adversary has access to protected discs.

This last requirement stems from the business strategies of the copy protection vendors. As discussed in earlier, many of these vendors are pursuing a platform building strategy. The biggest obstacle to the success of an active protection system is getting the protection software installed on client machines. Once installed, the software can regulate access to all discs protected by the scheme, even if the user learns to disable autorun or refuse future CD DRM installation requests. Thus each completed installation increases the effectiveness of the protection platform and heightens its value to the protection vendor and its music label clients.

Being widely installed adds value to these copy protection systems, but it also exposes them to a new class of attacks. The protection companies earn revenue from record labels who license their schemes, typically paying some fee per title or per copy. This revenue stream may be threatened if disc publishers can mark their discs as protected without paying.

There are advantages and disadvantages for the person placing the unauthorized marks. Copyright would prohibit rogue publishers from distributing an installer for the active protection software, though they might depend on the existing installed base from licensed titles. They would also be prevented from employing the components of the protection software that allow users to access restricted copies of the music; however, they could create their own software to provide this capability if they desired. On the other hand, free riding publishers would not be restricted to marking their disc for only one scheme. By identifying their discs as copy protected with multiple schemes, they could invoke multiple layers of security and provide stronger protection than is available with any single technique, all without paying. (It is possible that protection producers could have legal remedies against such free riders, such as through a patented identification feature, but we are unaware of any patents that cover the identification features known to be in use. Even if some kind of legal remedy is available, it’s worth designing the mark to prevent the problem too, at least if the cost of doing so is low.) Preventing free riding by publishers requires some kind of disc authentication mechanism to control access to installed active protection software—a meta-copy protection technique.

How MediaMax Recognizes Protected Discs

To find out how the disc recognition mechanisms employed by CD DRM systems stack up the ideal requirements, we examined the recognition system built into MediaMax CD-3 and MM-5 systems. The MediaMax system drew our attention because MediaMax’s creators have touted their advanced disc identification capabilities, including the ability to identify individual tracks within a compilation as protected, and well as their platform-building strategy. (The XCP scheme appears to use a less sophisticated disc recognition system based on a marker stored in the data track of protected discs. We may talk more about it later.)

We determined how MediaMax identifies protected albums by tracing the commands sent to the CD drive with and without the active protection software running. These experiments took place on a Windows XP virtual machine running on top of a Fedora Linux host system, which we modified by patching the kernel IDE-SCSI device to log all drive activity.

With this setup we observed that the MediaMax software executes a disc recognition procedure immediately upon the insertion of a CD. The MediaMax driver reads two sectors of audio data at a specific offset from the beginning of audio tracks—approximately 365 and 366 frames in (a CD frame is 1/75 second). On unprotected discs, the software scans through every track in this way, but on MediaMax-protected albums, it stops after the first three tracks, apparently having detected an identifying feature. The software decides whether or not to block read access to the audio solely on the basis of information in this region, so we inferred that the identifying mechanism takes the form of an inaudible watermark embedded in this part of the audio stream. (By locating the watermark nearly five seconds after the start of the track, MediaMax reduces the likelihood that it will occur in a very quiet passage, where it might be more audible, and makes it more difficult to crop out.)

Locating the watermark amid megabytes of audio might have been difficult, but we had the advantage of a virtual Rosetta Stone. The actual Rosetta Stone is a 1500 lb. granite slab unearthed by French archaeologists in Rosetta, Egypt, in 1799. A single Ptolemaic decree is written on the stone in three scripts: ancient hieroglyphics, demotic (simplified) hieroglyphics, and Greek. Comparing these inscriptions provided the key to deciphering Egyptian hieroglyphic texts. Our Rosetta Stone was a single album, Velvet Revolver’s Contraband (BMG, 2004), released in three different versions: a U.S. release protected by MediaMax, a European release protected by a passive scheme developed by Macrovision, and a Japanese release with no copy protection. We decoded the MediaMax watermark by examining the differences between the audio on these three discs. Binary comparison revealed no differences between the releases from Europe and Japan; however, the MediaMax-protected U.S. release differed slightly from the other two in certain parts of the recording. By carefully analyzing these differences—and repeatedly attempting to create new watermarked discs using the MediaMax active protection software as an oracle—we were able to deduce the structure of the watermark.

The MediaMax watermark is embedded into the audio of each track in 30 clusters. Each cluster is made up of 288 marked 16-bit audio samples followed by 104 unaltered samples. Three mark clusters exactly fit into one 2352-byte CD audio frame. The watermark is centered at approximately frame 365 of the track; though the detection routine in the software only reads two frames, the mark extends several frames to either side of the designated read target to allow for imprecise seeking in the audio portion of the disc (a typical shortcoming of inexpensive CD drives). The MediaMax driver detects the watermark if at least one mark cluster is present in the region read by the detector.

A sequence of 288 bits we call the raw watermark is embedded into the 288 marked audio samples of each mark cluster. A single bit of the raw watermark is embedded into an unmarked audio sample by setting one of the three least significant bits to the new bit value (as shown in bold) and then patching up the two other bits, according to this table:

(This design seems to be intended to lessen the audible distortion caused by by setting one of the bits to the watermark value. The change in the other two bits reduces the magnitude of the difference from the original audio sample, but it also introduces a highly uneven distribution in the three LSBs that makes the watermark easier to detect or remove.)

The position of the embedded bit in each sample follows a fixed sequence for every mark cluster. Each of the 288 bits is embedded in the first-, second-, or third-least-significant bit position of the sample according to this sequence:


The 288-bit raw watermark is detected by the active protection software only when it has certain properties, as shown in the sequence below. In the 288-bit sequence, 96 positions have fixed bit values, either 0 or 1. The trailing 32 positions have arbitrary values (as indicated by _), and can be used to store a 32-bit disc-specific value. The other 192 positions are divided into 32 groups of linked values (denoted az and alpha-zeta). In each group, three positions share the same value and three share the complement value. This allows the scheme to encode a second 32-bit value, though in actual discs it appears to be a different random value in each of the 30 mark clusters.

Attacks on the MediaMax Watermark

The MediaMax watermark fails to satisfy the indelibility and unforgeability requirements of an ideal disc recognition system. Far from being indelible, the mark is surprisingly brittle. Most advanced designs for robust audio watermarks manipulate the audio in the frequency domain and attempt to resist removal by lossy compression, multiple conversions between digital and analog formats, and other common transformation. In contrast, the MediaMax watermark is applied in the time domain and is rendered undetectable by even minor changes to the file. An adversary without any knowledge of the watermark’s design could remove it by converting the tracks to a lossy format like MP3 and then burning them back to a CD, which can be accomplished easily with standard consumer applications. This would result in some minor loss of fidelity, but a more sophisticated adversary could prevent the mark from being detected with almost no degradation by flipping the least significant of one carefully chosen sample from each of the 30 watermark clusters, thereby preventing the mark from exhibiting the pattern required by the detector.

The MediaMax watermark also fails to satisfy the unforgeability requirement. The mark’s only defense against forgery is its complicated, unpublished design, but as is often the case this security by obscurity has proved tedious rather than impossible to defeat. As it turns out, an adversary needs only limited knowledge of the watermark–its location within a protected track and its confinement to the three LSBs of each sample–to forge it with minimal loss of fidelity. Such an attacker could transplant the three LSBs of each sample within the watermarked region of a protected track to the corresponding sample from an unprotected one. Transplanting these bits would cause distortion more audible that that caused by embedding the watermark since the copied bits are likely to differ by a greater amount from the original sample values; however, the damage to the audio quality would be limited since the marked region is only 0.4 seconds in duration. A more sophisticated adversary could apply a watermark to an unprotected track by deducing the full details of the structure of the watermark, as we did; she could then embed the mark in an arbitrary audio file just as well a licensed disc producer.

Secure Disc Recognition

Having shown that the MediaMax watermark fails to provide either strong resistance to removal or strong resistance to forgery, we ask whether it is possible to securely accomplish either or both of these goals.

As far as indelibility is concerned, watermarking schemes have a poor history of resisting removal. This is especially true against an adversary who has oracle access to the watermark detector, as was the case with a previous application of watermarks to audio copy protection, SDMI, and with CD DRM systems. Making marks that are both indelible and unforgeable is likely much more difficult. There seems to be tension between marks that are difficult to remove and ones that are hard to forge. Enforcing both requirements creates two ways to fool the detector–by rendering the mark invisible and by making it appear forged. If, as in CD DRM, either situation leads to the same result (no protection), the attacker’s power is multiplied.

In contrast, a mark strongly robust to forgery is simple to create based on digital signatures if we aren’t concerned with its being easy to remove. A very simple scheme works as follows:

  • To sign an audio track, the licensed publisher reads a fixed portion L1 of the audio data (say, the first ten seconds), then computes a cryptographic hash of L1 and signs it using a public key signature algorithm to derive the signature SL1 := SignKS(Hash(L1)). SL1 is then stored at a second location in the track by setting the LSB of each sample in the region to the corresponding bit in the signature. A 320-bit DSA signature could be embedded in this way using approximately the same space as one mark cluster of the MediaMax watermark.

  • The publisher keeps the signing key KS secret, and builds the corresponding verification key KV into the client software. When presented with a CD, the software checks for a valid signature. First it reads the audio from the signed area of the track and hashes it, and it locates and extracts the signature stored in the LSBs in the second mark location. Next, it verifies the signature on the hash using KV. If the signature is correct, the watermark is valid and genuine; otherwise, forgery or data corruption is indicated.

Forging such a mark would require defeating the digital signature scheme or splicing both L1 and SL1 from a legitimately marked album. We set L1 to be several seconds of audio to make such splicing less appealing.

Clearly this watermark is highly vulnerable to removal. If even a single bit of the hashed region is changed, the mark will not be recognized as valid. Yet the watermark MediaMax actually uses is also vulnerable to corruption by a single bit too while being far less resistant to forgery. Robustness to removal, while desirable in principle, is of limited value in real CD DRM applications. Removal of the watermark is unlikely to be the weakest link protecting the audio, and while the gains from creating a more indelible watermark are slight, the loss to free riders from an easily forgeable mark is potentially much larger.


  1. Dave Sodee says

    I know I do not buy many cd’s anymore. I no longer trust Sony and I enjoy my computer. I will not risk my computer’s health to listen to some cd anymore. I find the same thing going in gaming nowadays as well. I will not buy any game that uses Star Force protection. It is just as invasive, can cause your dvd burner to die and opens up your system to potential hackers. It installs drivers on your system that stay on even after the game is uninstalled. It doesn’t hurt the pirates…but the consumer who would want the game. So …now I simply will not purchase that game if it has StarForce on it.

    Is this the goal?? I no longer buy music cds and now I am buying less games as well. Copy protection is working wonders…

  2. In reply to what Scott said: I have tried doing a follow the money research regarding a “slow down” of CD sales, it is very hard to get actual data but I used information from the RIAA’s web site and yes it did slow down, but I also got information from the disc replication industry and it shows much stronger sales when you combine CDs and DVDs quantity since the coming of DVDs. So my guess is that the entertainment industry which combines music and movie business which are rather well integrated is using a slow down in music sales to push new DRM related laws. The adoption of the CD or the DVD or any technology or new medium follows a bell curve shape when you analyse the market over several years. I think the CD is not an exception, once everyone has replaced their old cassettes and vinyls with brand new CDs the market has saturated and purchases slow down, no one buys 2 copies of an album except may for gifts or to replaced lost, broken or stolen disks.

  3. the zapkitty says

    Just a little fact, as opposed to lies. Factual data concerning the actual status of SuncMax products and claims… which, as we have seen, is in direct opposition to the claims SuncMax repeatedly makes on this very forum.

    You can’t have it both ways… you can’t spam a fact-based forum with lies about your company products and position when those same products are the subject of discussion… and then cry foul and “OT” when those lies are exposed.

    No. I do not think the SuncMax statements shouldn’t be left be when they are exposed as lies… even if the exposition is as off topic to a particular commentary as the original lies were.

    Of course you get into the sticky mess of repeated exposures and rendering the blog unreadable…

    …which describes SuncMax nicely, y’think? 🙂

    (“Bad zapkitty! No biscuit!”)

  4. Hey zipkitty, your last post contributes exactly WHAT to this forum?

    Is the play by play activity of a community that was established to discuss peoples investment into an equity this weblogs topic?

    After all, we have Edwards sarcasm and unprofessionalism here already!

    And oh ya, I am not a suncmax shill, just tired of your apparent agenda and off topic rhetoric. You’ve made your point.

  5. the zapkitty says

    Daniel W Says:
    According to Yahoo! Finnance, SunnComm stock closed at $0.014…

    That’s a fig leaf. Somebody threw in a couple of k to shove the ask price up over the weekend… after somebody else dumped two million shares at .0116 shortly before closing.

    They’ll be blaming the blog, of course, but the truth is far more ironic: one of the SuncMax shills made the mistake of telling the truth on the SuncMax I-Hub forum… the truth that there is no v6 product to put on CD’s (“yet”) despite the SuncMax web site claims to the contrary.

    Not long thereafter the hemorrhaging began… first a trickle, now a flood.

    ” – this justifies “we are back stronger than ever”?

    Perhaps not completely OT?… methinks this consistent lying and denial of reality is the very essence of SuncMax and its design philosophy as regards its DRM…

  6. I like how this new idea by Macrovision is what we have been able to do for ourselves since the CD burner became afordable by the home computer user.
    “TotalPlay CD encourages millions of consumers to put a CD into a PC for the first time by making the CD-to-PC-to-Portable experience simple and consistent. TotalPlay CD makes the CD a vital part of the portable digital revolution, instead of the part that’s being left behind. TotalPlay CD allows consumers to burn copies, share their music with friends, and create compilations. It offers a rich, graphical PC experience that gives content owners the ability to include extras like lyrics, album art, unlockable web downloads, video, games, photos and other exclusives.” (i.e. iTunes?)

    What’s new, the hidden phone-home, DRM solution or the new marketing name?

    And how does this press announcement for Macrovison indicate that SunnComm is alive and well? I didn’t see SunnComm’s name mentioned anywhere in the press release; in fact, the only refernce to outside parties is the statement “We continue to partner with the music industry…”. Is SummComm part of the music community now? According to Yahoo! Finnance, SunnComm stock closed at $0.014 – this justifies “we are back stronger than ever”?

    Back on topic – that was a most informative paper on the workings of MediaMax! Thank you, I’m looking forward to more along this vein.

  7. Regarding slowing CD sales, I’ve never seen anyone apply a “follow the money” approach to the alleged problem. I have not done any analysis, but my bet is that there would be a good correlation between the decrease in dollars spent on CDs and the increase in dollars spent on cell phone bills. As teens (or anyone else) with limited cash prioritize where to spend it, on CDs or on the cell phone, I can’t imagine the CDs winning. I see much of the illegal downloading being a consequence of people having little money left after paying the cell phone bill.

    If there any validity to this theory, DRM won’t improve CD sales because the money has already been spent.

  8. Wow,

    I hope we get the same in-depth write up on Macrovision’s NEW CD DRM. This, of course, won’t happen due to two factors….

    1) “Someone” is getting rewarded for their in-depth research on mediamax by Macrovision.


    2) Macrovision is far more likely to sue Princeton for a article similar to what was posted about Mediamax.

    Sure Halderman posted an article about Macrovision’s CD copy protection, that was an old version and not the new CDS300 type that DOES install software into your PC.

    There is an interesting bias and one thing that is certain…. This article was posted right in sync with Macrovision’s latest PR (yesterday) touting their DRM product.

  9. All bugs and performance issues aside, people dont like having rights they are used to having taken away. No matter how perfectly coded a DRM solution is, people are still going to be ticked off that they cannot make a mix CD.
    Companies complain about slowing CD sales, so they blame copyright infringement. While I am not condinging true copyright infringement (Warez, etc), mix CDs and the like sit firmly within fair use as far as I am concerned.
    So how do they stop copyright infringement?
    Attacking the users who legitimately buy their products.
    And they wonder why CD sales are dropping…

  10. Small typo: the word “bit” is left out of the sentence:

    This would result in some minor loss of fidelity, but a more sophisticated adversary could prevent the mark from being detected with almost no degradation by flipping the least significant of one carefully chosen sample from each of the 30 watermark clusters, thereby preventing the mark from exhibiting the pattern required by the detector.

  11. the zapkitty says

    While external matters shouldn’t effect the logic of a debate, the shills have a bad tendency to react to irrelevant pressures. Be aware that Sunncomm stock went into freefall yesterday and is heading down from out of the gate today.

    (In other words be prepared for yet even more hysterics from the shills…)

  12. Edward Kuns says


    If you post factual, verifiable information about your competitor’s products, people will believe you after they verify your allegations. If you post only allegations, however, then no-one will believe you.

    Also, it’s “for all intents and purposes” and not “for all intensive purposes.”

  13. Your sarcasm noted and unprofessionalism acknowledged!

  14. It was just one minor bug that couldn’t be exploited easily anyway. Give us a break. How many programs do you think are completely bug free. The other issues were there because Sony requested them.

  15. Anonymous,

    Too bad SunnComm didn’t investigate their own software as thoroughly as (you say) they investigated their competitor’s.

  16. Two questions:

    1. Please explain the term “oracle access.”

    2. A question: in listing vulnerabilities of DRM schemes, shouldn’t one be listed that refers to whether or not each instance of use is unique, i.e., if I stamp out CD’s and each is identical, don’t I run the risk of: if one’s protection is “broken,” the prrotection of ALL is broken? (I’m thinking here of the old cryptographic concept of using one-time keys in encryption/decryption of individual messages).

    PS: Please let us know when the “cease and desist” letters start arriving.

  17. I like the part about monitoring the drive access via a VM running Windows inside Linux.

    Was there any attempt to analyze the operation of the Suncomm binaries? If not, I would be interested to know if that was for technical, practical, or legal reasons. Or if they were analyzed, did that work bear any fruit?

  18. the zapkitty says

    But which version of Mediamax is being examined?

    SuncMax released yet another patch for their patch… and as yet no feedback anywhere on what the new problems are supposed to be, or how this patch is supposed to fix them, or even what the hell people are being asked to download into their systems now


    “Important Security Notice:

    It has come to our attention that a security vulnerability may exist with regard to Version 5 of SunnComm’s MediaMax content protection software. To address this potential security issue, SunnComm has made available a software update. Click here to download the update (January 25, 2006).”

    ? ? ? ? ?

  19. Steve C Says:

    “Why don’t the folks who complain about Ed not analysing Macrovision take the initiative and analyse it themselves?”

    Well the folks at SunnComm have analysed CDS and have found it to be buggy, act like spyware and use rootkits too. But for all intensive purposes who would believe SunnComm if they published those facts. Why should we help the competition fix there problems. You are the ones that claim to be independent, yet its all one way.

    SunnComm were aware of the XCP problems rootkit problems too long before you lot even knew what a rootkit was.

    Just check this out from one of our very astute posters.


    For those suggesting SunnComm are dead and buried, you better realise that we are back stronger than ever.


  20. Perhaps the greatest difficulty of watermarking is constructing a watermark that will defy differential analysis. It would be very rare that content would only be released with one style of watermark; if someone has copies of content with two or more different watermarks, or of watermarked and unwatermarked versions, it becomes possible to identify the watermark information. This in turn makes it possible to filter or remove it.

  21. Edward Kuns says

    This is a little bit off the topic, and perhaps off the topic of the paper being worked on (but maybe not), but I wonder about the longer term implications about companies seeing this sort of active, intrusive DRM as a regular business tool. If this occurs, then this kind of software will go beyond just music CDs and other common media formats.

  22. Scott,

    You have good eyes. I accidentally erased those overbars when I resized the figure for the web. Reload the page to get a fixed version. Thanks for pointing this out.

  23. Wow – very detailed and VERY well done.

    A bit of that went over my head but on the whole its very impressive.

  24. Ned Ulbricht says

    I’d suggest redrafting the explanation of the raw watermark so that the discussion of Table 1 occurs after the discussion of the 2,3,1,1… sequence. Reading the first time, I was confused by the “Marked bits” of the table until finally I went on and read about the sequence. Then I was able to backtrack and understand Table 1.

  25. Steve Gaede says

    I think that your Rosetta stone analogy is brilliant, and it ties your technique to something ancient and timeless. It takes the discussion far away from arguments that what you’re doing is DMCA-prohibited “reverse engineering,” and instead ties it to analysis that has been legal for hundreds of years.

  26. Are free riders (foregeability) really a concern to DRM producers? If Capitol Records started forging Sony’s protections, it would be simple for Sony to sue them for infringement, and collect.

    If small labels forged the protection, their total impact would be negligible because the amount of forging going on would be tiny. As soon as any one label grew to any significant size, they would be easier to sue.

    Therefore, large groups that might be a problem as free riders would automatically avoid forging as soon as they had anything financially to lose in a suit.

    So making a DRM scheme unforgeable is in practice, of low importance, right?

  27. (These typos happen to be easy to spot by eye, since three k’s and three deltas all appear in the last two rows of the figure, after appearing once more at their “usual” alphabetic position.)

  28. Whoops, the four ~a’s were due to my transcription error, and i meant ‘k’ when I said ‘g’ above. But there are still four ks and only two ~ks, and four deltas and two ~deltas. This seems to indicate two missing overbars.

  29. You write, “In each group, three positions share the same value and three share the complement value.” but there appear to be *four* of g, delta, and ~a. Is this a typo?

  30. Possibly I’ve just missed it, but I haven’t seen anyone asking to be fed by the trolls. So…

    Why don’t the folks who complain about Ed not analysing Macrovision take the initiative and analyse it themselves?

  31. Nice work. It shows once again that steganography or watermarking techniques which use simple LSBs only are often very weak. Just a (probably stupid) question, out of curiosity : did you use your differential “Rosetta Stone” method (comparing one marked and one unmarked version of the same files) because it was technically easier than tracing the drivers, or because of the legal implications of disassembling the drivers (DMCA about “circumventing copy protection technology”, I guess you know what I’m talking about better than anyone) ? In other words, do you chose your analysis method because of technical or legal reasons ?

    Well. Don’t bother. I guess just by writing the question, I already replied to it, in a way 🙂

  32. Since the Sunncomm shill entered the fray; I have one observation from Dr. Felton’s post. The application of any DRM product on a personal computer corrupts (degrades) its performance besides the issue that the DRM company is tresspassing on your computer and making “unauthorized” changes to the operating system. DRM, as we all know will NOT work. Yet Sony/Suncomm are persisting. There is an alternative that we have not explored. I have come to the conclusion that if Sony/Sunncomm want to sell a DRM based product, that both the CD/DVD and the PLAYER itself should be designed as an integrated system that will NOT work on your PC or regular CD player. Skip backward compatibility.

    I simply do not want to see industry based laws that force my computer (cripple) hardware to support DRM technology. If Sony/Suncomm want to protect their intellectual property, they are free to design a fully proprietary CD/DVD system and proprietary player that will only operate with their products. We are headed that road way anyway, through software that mysteriously disables the ability of the CD burner to work when it detects a competitor’s product. Sony by developing its own proprietary platform wuld still allow those who want to buy a Sony product to do so. Those of us who don’t won’t. End of argument.

  33. Paul,

    I imagine the free rider as a record label that has decided it wants to deploy DRM, and would prefer to to so (at somewhat reduced effectiveness) without paying a fee to the DRM vendor. If the record label thinks that DRM won’t help it (which, as you note, is quite plausible), then the record company won’t use DRM in any case.

    A DRM vendor can stop the scenario in your last paragraph by contract, by requiring labels who license the DRM for any of their discs to promise not to put marks on other discs without paying. This will work against big labels. Contracts can’t stop labels who don’t do business with the DRM vendor, because there aren’t any contracts in which the no-free-riding clause can be put.

  34. What’s the market model of the free rider? They get to make their recordings (not properly speaking CDs) less attractive to consumers without paying quite as much for the privilege, and perhaps they get the extra revenues from pay-for-download, a but it’s not clear the losses and the benefits balance. Furthermore, a free-rider would almost certainly have to be a fairly small-volume producer, because they’re relying on enough members of their target market being infected with someone else’s DRM kit, which is unlikely if they dominate. (And if they’re a small player in the market, DRM free-riding or otherwise probably isn’t their best investment)

    Depending on how contracts are worded and who has more money for lawyers, free-riding might be more attractive for large record companies who already employ DRM: a few mega-selling CDs, perhaps even specially priced, would carry the DRM installer, and the rest of the catalog would merely be marked as restricted.

  35. Heh. Anonymous Suncomm shill — such gloom and doom? Why not recognize that Prof. Felten is in fact doing all your engineering work for the next version of your product for you? It would cost you big bucks to get such a detailed analysis of your product and suggestions for improvements — but he’s giving it to you for free!

    Serious comments:

    The Rosetta stone description seems a little verbose and out-of-place in a technical paper with tight length requirements. Why not just say, “…The real 1500 lb granite Rosetta Stone contains inscriptions in ancient hieroglyphics, demotic (simplified) hieroglyphics, and Greek; comparing these inscriptions proved the key to deciphering Egyptian hieroglyphic texts. Our Rosetta stone was Velvet Revolver’s Contraband…”

    Also I was looking for the “payoff” sentence somewhere in the article about the dangers of releasing versions of albums differing only in their DRM in this age of exact binary reproduction. The cryptographically-inclined among us see this conclusion as obvious, but it should be given an explicit statement somewhere. DRM vendors, insist on exclusivity!

    Also, the tension between forgery and robustness seems to want a full paragraph describing (at least in outline form) an easily-forgable watermark that nevertheless is very robust. This would satisfy the parallelism set up, but I can’t think of a good academic example of such a system. You mention “Most advanced designs for robust audio watermarks manipulate the audio in the frequency domain and attempt to resist removal by lossy compression, multiple conversions between digital and analog formats, and other common transformation.” in the MediaMax section, but maybe this brief discussion of frequency-domain watermarks should be moved to the “Secure Disc Recognition” section. This is just an idea; it would be a much stronger suggestion if I could think of even an academically-interesting-but-impractical pedagogical example of a robust-but-forgeable watermark. Maybe you can.

    Finally, the bit pattern you discuss seems to be as if it could be more compactly represented as X*a ^ Y*(~a) ^ b ^ Z, where a and b are freely-chosen 32-bit numbers to be encoded, and X, Y, and Z are carefully chosen 287-bit numbers. Maybe I’ve got the arithmetic slightly wrong, but multiplication should be able to distribute the bits of ‘a’ in roughly the right places; you can cancel out the ones in the wrong places with the xor and ~a; and Z will set the final ‘1s’ in the result. I guess this would be more convenient for encoding, but would not as compactly represent the invariants which the mark-recognizer would check.

  36. Thanks for the great details on MediaMax. It’s pretty clear that these DRM solutions have a long way to go before they meet the durability and unforgeablity requirements. The fact that the current approaches fall so far short of the mark raises some interesting questions.

    Regarding Macrovision – a bit of web searching suggests that they have been beta testing their CDS 300 product for several years now. The Register had a review of an early version back in 2004 here:


    This article suggests that their approach was much less complex and would have been fairly easy to bypass. There doesn’t seem to be much recent research on it however, so it’s difficult to say what it’s like today.

    Of course all of these DRM solutions fall apart when using the protected content in an unsupported operation system. MacOS X and the various flavors of Linux & Unix all seem fairly immune to these protection mechanisms.

  37. Edward Kuns says

    Ugghhhhh. I made the same media/vision typo as BooHoo. At least I was correct in later paragraphs. And when I Googled, I used the correct company name.

  38. Edward Kuns says

    Anon, can you provide even one link to a page giving evidence about Macromedia DRM being spyware and installing a rootkit? Googling on my part didn’t turn anything up. If, as I imagine, there is no such page, then you’re trying to spread FUD to divert people from looking at the facts about your company.

    Also, the presence of an alum from a college on the BOD of a company is a tenuous tie between the company and the college. The continuing allegation by Suncomm/F4I folks that this link is evidence of a connection between the two is, well, it’s a very weak allegation.

    I too would love to see the Macrovision CDS300 investigated so we all know precisely what sort of risks or costs it provides the CD purchaser. Note that the passive elements of Macrovision protection have been discussed here as recently as 15 Dec 2005:


    P.S. If Princeton or if this group is being paid by Macrovision to investigate their rivals, then there will exist a paper trail proving this to be so. I challenge you to find us any evidence of such a connection. In the absence of such evidence, your continuing allegation gets weaker with every repetition.

  39. BooHoo: s/Macromedia/Macrovision

  40. The SEC is only concerned with SECURITIES violations, not CRIMINAL INVASION of individual computers. I agree with you about investigating Macromedia as well–there is one popular CAD software company that will lose my wife’s business because they use Macromedia’s software; however, this doesn’t lessen your company’s responsibility to be ethical. If you are in charge of MediaMax, then I would change the purpose of my company if I were you.

    Any copy protection scheme that is invasive is also unethical. Such schemes are often defeated by organized pirates and are not necessary for regular consumers–and in fact violate consumers’ fair-use rights as well as install malicious software onto consumers’ computers without permission (which is illegal, last time I checked).

  41. I think you should own up and admit you are being paid by our competition to expose the inner workings of our product. We know there is a Princeton alumni on the Macrovision BOD. Everyone knows there product is spyware and installs rootkits, but you never bother to investigate it. Why not? I also notice this blog is been used to attack the integrity of our company. Why do you allow unfounded allegations about sham deals and the like. If our company did anything wrong the SEC would be all over them, yet the SEC hasn’t ever charged us with anything.

  42. Wow, very detailed and extremely well done. Have we just witnessed another example of posting DeCSS here? Should we start a count down before someone gets a letter from a lawyer or a knock on the door by the FBI?

  43. Why oh why must you taunt the Sunncomm shills? 🙂

    I get the feeling that Sunncomm did not even consider the indelibility or unforgeability problem, perhaps for the very reasons you mention. They most likely told the record labels, “we can’t fix that; get Congress to pass a law making it illegal.”