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Do NOT buy Windows Vista
« on: December 24, 2006, 03:12:23 PM »
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  • And I thought Windows XP was bad!!

               A Cost Analysis of Windows Vista Content Protection

                    Peter Gutmann,
                         Last updated 23 December 2006

    Executive Summary

    Windows Vista includes an extensive reworking of core OS elements in order to
    provide content protection for so-called "premium content", typically HD data
    from Blu-Ray and HD-DVD sources.  Providing this protection incurs
    considerable costs in terms of system performance, system stability, technical
    support overhead, and hardware and software cost.  These issues affect not
    only users of Vista but the entire PC industry, since the effects of the
    protection measures extend to cover all hardware and software that will ever
    come into contact with Vista, even if it's not used directly with Vista (for
    example hardware in a Macintosh computer or on a Linux server).  This document
    analyses the cost involved in Vista's content protection, and the collateral
    damage that this incurs throughout the computer industry.

    Executive Executive Summary

    The Vista Content Protection specification could very well constitute the
    longest suicide note in history.


    This document looks purely at the cost of the technical portions of Vista's
    content protection.  The political issues (under the heading of DRM) have been
    examined in exhaustive detail elsewhere and won't be commented on further,
    unless it's relevant to the cost analysis.  However, one important point that
    must be kept in mind when reading this document is that in order to work,
    Vista's content protection must be able to violate the laws of physics,
    something that's unlikely to happen no matter how much the content industry
    wishes it were possible.  This conundrum is displayed over and over again in
    the Windows content-protection specs, with manufacturers being given no hard-
    and-fast guidelines but instead being instructed that they need to display as
    much dedication as possible to the party line.  The documentation is peppered
    with sentences like:

      "It is recommended that a graphics manufacturer go beyond the strict letter
      of the specification and provide additional content-protection features,
      because this demonstrates their strong intent to protect premium content".

    This is an exceedingly strange way to write technical specifications, but is
    dictated by the fact that what the spec is trying to achieve is fundamentally
    impossible.  Readers should keep this requirement to display appropriate
    levels of dedication in mind when reading the following analysis [Note A].

    Disabling of Functionality

    Vista's content protection mechanism only allows protected content to be sent
    over interfaces that also have content-protection facilities built in.
    Currently the most common high-end audio output interface is S/PDIF
    (Sony/Philips Digital Interface Format).  Most newer audio cards, for example,
    feature TOSlink digital optical output for high-quality sound reproduction,
    and even the latest crop of motherboards with integrated audio provide at
    least coax (and often optical) digital output.  Since S/PDIF doesn't provide
    any content protection, Vista requires that it be disabled when playing
    protected content.  In other words if you've invested a pile of money into a
    high-end audio setup fed from a digital output, you won't be able to use it
    with protected content.  Similarly, component (YPbPr) video will be disabled
    by Vista's content protection, so the same applies to a high-end video setup
    fed from component video.

    Indirect Disabling of Functionality

    As well as overt disabling of functionality, there's also covert disabling of
    functionality.  For example PC voice communications rely on automatic echo
    cancellation (AEC) in order to work.  AEC requires feeding back a sample of
    the audio mix into the echo cancellation subsystem, but with Vista's content
    protection this isn't permitted any more because this might allow access to
    premium content.  What is permitted is a highly-degraded form of feedback that
    might possibly still sort-of be enough for some sort of minimal echo
    cancellation purposes.

    The requirement to disable audio and video output plays havoc with standard
    system operations, because the security policy used is a so-called "system
    high" policy: The overall sensitivity level is that of the most sensitive data
    present in the system.  So the instant any audio derived from premium content
    appears on your system, signal degradation and disabling of outputs will
    occur.  What makes this particularly entertaining is the fact that the
    downgrading/disabling is dynamic, so if the premium-content signal is
    intermittent or varies (for example music that fades out), various outputs and
    output quality will fade in and out, or turn on and off, in sync.  Normally
    this behaviour would be a trigger for reinstalling device drivers or even a
    warranty return of the affected hardware, but in this case it's just a signal
    that everything is functioning as intended.

    Decreased Playback Quality

    Alongside the all-or-nothing approach of disabling output, Vista requires that
    any interface that provides high-quality output degrade the signal quality
    that passes through it.  This is done through a "constrictor" that downgrades
    the signal to a much lower-quality one, then up-scales it again back to the
    original spec, but with a significant loss in quality.  So if you're using an
    expensive new LCD display fed from a high-quality DVI signal on your video
    card and there's protected content present, the picture you're going to see
    will be, as the spec puts it, "slightly fuzzy", a bit like a 10-year-old CRT
    monitor that you picked up for $2 at a yard sale.  In fact the spec
    specifically still allows for old VGA analog outputs, but even that's only
    because disallowing them would upset too many existing owners of analog
    monitors.  In the future even analog VGA output will probably have to be
    disabled.  The only thing that seems to be explicitly allowed is the extremely
    low-quality TV-out, provided that Macrovision is applied to it.

    The same deliberate degrading of playback quality applies to audio, with the
    audio being downgraded to sound (from the spec) "fuzzy with less detail".

    Amusingly, the Vista content protection docs say that it'll be left to
    graphics chip manufacturers to differentiate their product based on
    (deliberately degraded) video quality.  This seems a bit like breaking the
    legs of Olympic athletes and then rating them based on how fast they can
    hobble on crutches.

    Beyond the obvious playback-quality implications of deliberately degraded
    output, this measure can have serious repercussions in applications where
    high-quality reproduction of content is vital.  For example the field of
    medical imaging either bans outright or strongly frowns on any form of lossy
    compression because artifacts introduced by the compression process can cause
    mis-diagnoses and in extreme cases even become life-threatening.  Consider a
    medical IT worker who's using a medical imaging PC while listening to
    audio/video played back by the computer (the CDROM drives installed in
    workplace PCs inevitably spend most of their working lives playing music or
    MP3 CDs to drown out workplace noise).  If there's any premium content present
    in there, the image will be subtly altered by Vista's content protection,
    potentially creating exactly the life-threatening situation that the medical
    industry has worked so hard to avoid.  The scary thing is that there's no easy
    way around this - Vista will silently modify displayed content under certain
    (almost impossible-to-predict in advance) situations discernable only to
    Vista's built-in content-protection subsystem.

    Elimination of Open-source Hardware Support

    In order to prevent the creation of hardware emulators of protected output
    devices, Vista requires a Hardware Functionality Scan (HFS) that can be used
    to uniquely fingerprint a hardware device to ensure that it's (probably)
    genuine.  In order to do this, the driver on the host PC performs an operation
    in the hardware (for example rendering 3D content in a graphics card) that
    produces a result that's unique to that device type.

    In order for this to work, the spec requires that the operational details of
    the device be kept confidential.  Obviously anyone who knows enough about the
    workings of a device to operate it and to write a third-party driver for it
    (for example one for an open-source OS, or in general just any non-Windows OS)
    will also know enough to fake the HFS process.  The only way to protect the
    HFS process therefore is to not release any technical details on the device
    beyond a minimum required for web site reviews and comparison with other

    Elimination of Unified Drivers

    The HFS process has another cost involved with it.  Most hardware vendors have
    (thankfully) moved to unified driver models instead of the plethora of
    individual drivers that abounded some years ago.  Since HFS requires unique
    identification and handling of not just each device type (for example each
    graphics chip) but each variant of each device type (for example each stepping
    of each graphics chip) to handle the situation where a problem is found with
    one variation of a device, it's no longer possible to create one-size-fits-all
    drivers for an entire range of devices like the current
    Catalyst/Detonator/ForceWare drivers.  Every little variation of every device
    type out there must now be individually accommodated in custom code in order
    for the HFS process to be fully effective.

    If a graphics chip is integrated directly into the motherboard and there's no
    easy access to the device bus then the need for bus encryption (see
    "Unnecessary CPU Resource Consumption" below) is removed.  Because the
    encryption requirement is so onerous, it's quite possible that this means of
    providing graphics capabilities will suddenly become more popular after the
    release of Vista.  However, this leads to a problem: It's no longer possible
    to tell if a graphics chip is situated on a plug-in card or attached to the
    motherboard, since as far as the system is concerned they're both just devices
    sitting on the AGP/PCIe bus.  The solution to this problem is to make the two
    deliberately incompatible, so that HFS can detect a chip on a plug-in card vs.
    one on the motherboard.  Again, this does nothing more than increase costs and
    driver complexity.

    Further problems occur with audio drivers.  To the system, HDMI audio looks
    like S/PDIF, a deliberate design decision to make handling of drivers easier.
    In order to provide the ability to disable output, it's necessary to make HDMI
    codecs deliberately incompatible with S/PDIF codecs, despite the fact that
    they were specifically designed to appear identical in order to ease driver
    support and reduce development costs.

    Denial-of-Service via Driver Revocation

    Once a weakness is found in a particular driver or device, that driver will
    have its signature revoked by Microsoft, which means that it will cease to
    function (details on this are a bit vague here, presumably some minimum
    functionality like generic 640x480 VGA support will still be available in
    order for the system to boot).  This means that a report of a compromise of a
    particular driver or device will cause all support for that device worldwide
    to be turned off until a fix can be found.  Again, details are sketchy, but if
    it's a device problem then presumably the device turns into a paperweight once
    it's revoked.  If it's an older device for which the vendor isn't interested
    in rewriting their drivers (and in the fast-moving hardware market most
    devices enter "legacy" status within a year of two of their replacement models
    becoming available), all devices of that type worldwide become permanently

    The threat of driver revocation is the ultimate nuclear option, the crack of
    the commissars' pistols reminding the faithful of their duty [Note B].  The
    exact details of the hammer that vendors will be hit with is buried in
    confidential licensing agreements, but I've heard mention of multimillion
    dollar fines and embargoes on further shipment of devices alongside the driver
    revocation mentioned above.

    Decreased System Reliability

      "Drivers must be extra-robust.  Requires additional driver development to
      isolate and protect sensitive code paths" -- ATI.

    Vista's content protection requires that devices (hardware and software
    drivers) set so-called "tilt bits" if they detect anything unusual.  For
    example if there are unusual voltage fluctuations, maybe some jitter on bus
    signals, a slightly funny return code from a function call, a device register
    that doesn't contain quite the value that was expected, or anything similar, a
    tilt bit gets set.  Such occurrences aren't too uncommon in a typical computer
    (for example starting up or plugging in a bus-powered device may cause a small
    glitch in power supply voltages, or drivers may not quite manage device state
    as precisely as they think).  Previously this was no problem - the system was
    designed with a bit of resilience, and things will function as normal.  In
    other words small variances in performance are a normal part of system
    functioning. Furthermore, the degree of variance can differ widely across
    systems, with some handling large changes in system parameters and others only
    small ones.  One very obvious way to observe this is what happens when a bunch
    of PCs get hit by a momentary power outage.  Effects will vary from powering
    down, to various types of crash, to nothing at all, all triggered by exactly
    the same external event.

    With the introduction of tilt bits, all of this designed-in resilience is
    gone.  Every little (normally unnoticeable) glitch is suddenly surfaced
    because it could be a sign of a hack attack.  The effect that this will have
    on system reliability should require no further explanation.

    Content-protection "features" like tilt bits also have worrying denial-of-
    service (DoS) implications.  It's probably a good thing that modern malware is
    created by programmers with the commercial interests of the phishing and spam
    industries in mind rather than just creating as much havoc as possible.  With
    the number of easily-accessible grenade pins that Vista's content protection
    provides, any piece of malware that decides to pull a few of them will cause
    considerable damage.  The homeland security implications of this seem quite
    serious, since a tiny, easily-hidden piece of malware would be enough to
    render a machine unusable, while the very nature of Vista's content protection
    would make it almost impossible to determine why the denial-of-service is
    occurring.  Furthermore, the malware authors, who are taking advantage of
    "content-protection" features, would be protected by the DMCA against any
    attempts to reverse-engineer or disable the content-protection "features" that
    they're abusing.

    Even without deliberate abuse by malware, the homeland security implications
    of an external agent being empowered to turn off your IT infrastructure in
    response to a content leak discovered in some chipset that you coincidentally
    happen to be using is a serious concern for potential Vista users.  Non-US
    governments are already nervous enough about using a US-supplied operating
    system without having this remote DoS capability built into the operating
    system.  And like the medical-image-degradation issue, you won't find out
    about this until it's too late, turning Vista PCs into ticking time bombs if
    the revocation functionality is ever employed.

    Increased Hardware Costs

      "Cannot go to market until it works to specification... potentially more
      respins of hardware" -- ATI.

      "This increases motherboard design costs, increases lead times, and reduces
      OEM configuration flexibility.  This cost is passed on to purchasers of
      multimedia PCs and may delay availability of high-performance platforms" --

    Vista includes various requirements for "robustness" in which the content
    industry, through "hardware robustness rules", dictates design requirements to
    hardware manufacturers.  For example, only certain layouts of a board are
    allowed in order to make it harder for outsiders to access parts of the board.
    Possibly for the first time ever, computer design is being dictated not by
    electronic design rules, physical layout requirements, and thermal issues, but
    by the wishes of the content industry. Apart from the massive headache that
    this poses to device manufacturers, it also imposes additional increased costs
    beyond the ones incurred simply by having to lay out board designs in a
    suboptimal manner.  Video card manufacturers typically produce a one-size-
    fits-all design (often a minimally-altered copy of the chipset vendor's
    reference design), and then populate different classes and price levels of
    cards in different ways.  For example a low-end card will have low-cost,
    minimal or absent TV-out encoders, DVI circuitry, RAMDACs, and various other
    add-ons used to differentiate budget from premium video cards. You can see
    this on the cheaper cards by observing the unpopulated bond pads on circuit
    boards, and gamers and the like will be familiar with cut-a-trace/resolder-a-
    resistor sidegrades of video cards. Vista's content-protection requirements
    eliminate this one-size-fits-all design, banning the use of separate TV-out
    encoders, DVI circuitry, RAMDACs, and other discretionary add-ons.  Everything
    has to be custom-designed and laid out so that there are no unnecessary
    accessible signal links on the board.  This means that a low-cost card isn't
    just a high-cost card with components omitted, and conversely a high-cost card
    isn't just a low-cost card with additional discretionary components added,
    each one has to be a completely custom design created to ensure that no signal
    on the board is accessible.

    This extends beyond simple board design all the way down to chip design.
    Instead of adding an external DVI chip, it now has to be integrated into the
    graphics chip, along with any other functionality normally supplied by an
    external chip.  So instead of varying video card cost based on optional
    components, the chipset vendor now has to integrate everything into a one-
    size-fits-all premium-featured graphics chip, even if all the user wants is a
    budget card for their kids' PC.

    Increased Cost due to Requirement to License Unnecessary Third-party IP

      "We've taken on more legal costs in copyright protection in the last six to
      eight months than we have in any previous engagement.  Each legal contract
      sets a new precedent, and each new one builds on the previous one" -- ATI.

    Protecting all of this precious premium content requires a lot of additional
    technology.  Unfortunately much of this is owned by third parties and requires
    additional licensing.  For example HDCP for HDMI is owned by Intel, so in
    order to send a signal over HDMI you have to pay royalties to Intel, even
    though you could do exactly the same thing for free over DVI.  Similarly,
    since even AES-128 on a modern CPU isn't fast enough to encrypt high-bandwidth
    content, companies are required to license the Intel-owned Cascaded Cipher, an
    AES-128-based transform that's designed to offer a generally similar level of
    security but with less processing overhead.

    The need to obtain unnecessary technology licenses extends beyond basic
    hardware IP.  In order to demonstrate their commitment to the cause, Microsoft
    have recommended as part of their "robustness rules" that vendors license
    third-party code obfuscation tools to provide virus-like stealth capabilities
    for their device drivers in order to make it difficult to interfere with their
    operations or reverse-engineer them.  Vendors like Cloakware and Arxan have
    actually added "robustness solutions" web pages to their sites in anticipation
    of this lucrative market.  This must be a nightmare for device vendors, for
    whom it's already enough of a task getting fully functional drivers deployed
    without having to deal with adding stealth-virus-like technology on top of the
    basic driver functionality.

    Unnecessary CPU Resource Consumption

      "Since [encryption] uses CPU cycles, an OEM may have to bump the speed grade
      on the CPU to maintain equivalent multimedia performance.  This cost is
      passed on to purchasers of multimedia PCs" -- ATI.

    In order to prevent tampering with in-system communications, all communication
    flows have to be encrypted and/or authenticated.  For example content to video
    cards has to be encrypted with AES-128.  This requirement for cryptography
    extends beyond basic content encryption to encompass not just data flowing
    over various buses but also command and control data flowing between software
    components.  For example communications between user-mode and kernel-mode
    components are authenticated with OMAC message authentication-code tags, at
    considerable cost to both ends of the connection.

    In order to prevent active attacks, device drivers are required to poll the
    underlying hardware every 30ms to ensure that everything appears kosher.  This
    means that even with nothing else happening in the system, a mass of assorted
    drivers has to wake up thirty times a second just to ensure that... nothing
    continues to happen.  In addition to this polling, further device-specific
    polling is also done, for example Vista polls video devices on each video
    frame displayed in order to check that all of the grenade pins (tilt bits) are
    still as they should be [Note C].

    On-board graphics create an additional problem in that blocks of precious
    content will end up stored in system memory, from where they could be paged to
    disk.  In order to avoid this, Vista tags such pages with a special protection
    bit indicating that they need to be encrypted before being paged out and
    decrypted again after being paged in.  Vista doesn't provide any other
    pagefile encryption, and will quite happily page banking PINs, credit card
    details, private, personal data, and other sensitive information, in
    plaintext.  The content-protection requirements make it fairly clear that in
    Microsoft's eyes a frame of premium content is worth more than (say) a user's
    medical records or their banking PIN.

    In addition to the CPU costs, the desire to render data inaccessible at any
    level means that video decompression can't be done in the CPU any more, since
    there isn't sufficient CPU power available to both decompress the video and
    encrypt the resulting uncompressed data stream to the video card.  As a
    result, much of the decompression has to be integrated into the graphics chip.
    At a minimum this includes IDCT, MPEG motion compensation, and the Windows
    Media VC-1 codec (which is also DCT-based, so support via an IDCT core is
    fairly easy).  As a corollary to the "Increased Hardware Costs" problem above,
    this means that you can't ship a low-end graphics chip without video codec
    support any more.

    The inability to perform decoding in software also means that any premium-
    content compression scheme not supported by the graphics hardware can't be
    implemented.  If things like the Ogg video codec ever eventuate and get used
    for premium content, they had better be done using something like Windows
    Media VC-1 or they'll be a non-starter under Vista or Vista-approved hardware.
    This is particularly troubling for the high-quality digital cinema (D-Cinema)
    specification, which uses Motion JPEG2000 (MJ2K) because standard MPEG and
    equivalents don't provide sufficient image quality.  Since JPEG2000 uses
    wavelet-based compression rather than MPEG's DCT-based compression, and
    wavelet-based compression isn't on the hardware codec list, it's not possible
    to play back D-Cinema premium content (the moribund Ogg Tarkin codec also used
    wavelet-based compression).  Because *all* D-Cinema content will (presumably)
    be premium content, the result is no playback at all until the hardware
    support appears in PCs at some indeterminate point in the future.  Compare
    this to the situation with MPEG video, where early software codecs like the
    XingMPEG en/decoder practically created the market for PC video.  Today, thanks
    to Vista's content protection, the opening up of new markets in this manner
    would be impossible.

    The high-end graphics and audio market are dominated entirely by gamers, who
    will do anything to gain the tiniest bit of extra performance, like buying
    Bigfoot Networks' $250 "Killer NIC" ethernet card in the hope that it'll help
    reduce their network latency by a few milliseconds.  These are people buying
    $500-$1000 graphics and sound cards for which one single sale brings the
    device vendors more than the few cents they get from the video/audio portion
    of an entire roomful of integrated-graphics-and-sound PCs.  I wonder how this
    market segment will react to knowing that their top-of-the-line hardware is
    being hamstrung by all of the content-protection "features" that Vista hogties
    it with?

    Unnecessary Device Resource Consumption

      "Compliance rules require [content] to be encrypted.  This requires
      additional encryption/decryption logic thus adding to VPU costs.  This cost
      is passed on to all consumers" -- ATI.

    As part of the bus-protection scheme, devices are required to implement
    AES-128 encryption in order to receive content from Vista.  This has to be
    done via a hardware decryption engine on the graphics chip, which would
    typically be implemented by throwing away a rendering pipeline or two to make
    room for the AES engine.

    Establishing the AES key with the device hardware requires further
    cryptographic overhead, in this case a 2048-bit Diffie-Hellman key exchange.
    In programmable devices this can be done (with considerable effort) in the
    device (for example in programmable shader hardware), or more simply by
    throwing out a few more rendering pipelines and implementing a public-key-
    cryptography engine in the freed-up space.

    Needless to say, the need to develop, test, and integrate encryption engines
    into audio/video devices will only add to their cost, as covered in "Increased
    Hardware Costs" above, and the fact that their losing precious performance in
    order to accommodate Vista's content protection will make gamers less than

    Final Thoughts

      "No amount of coordination will be successful unless it's designed with the
      needs of the customer in mind.  Microsoft believes that a good user
      experience is a requirement for adoption" -- Microsoft.

      "The PC industry is committed to providing content protection on the PC, but
      nothing comes for free.  These costs are passed on to the consumer" -- ATI.

    At the end of all this, the question remains: Why is Microsoft going to this
    much trouble?  Ask most people what they picture when you use the term
    "premium media player" and they'll respond with "A PVR" or "A DVD player" and
    not "A Windows PC".  So why go to this much effort to try and turn the PC into
    something that it's not?

    In July 2006, Cory Doctorow published an analysis of the anti-competitive
    nature of Apple's iTunes copy-restriction system ("Apple's Copy Protection
    Isn't Just Bad For Consumers, It's Bad For Business", Cory Doctorow,
    Information Week, 31 July 2006).  The only reason I can imagine why Microsoft
    would put its programmers, device vendors, third-party developers, and
    ultimately its customers, through this much pain is because once this copy
    protection is entrenched, Microsoft will completely own the distribution
    channel.  In the same way that Apple has managed to acquire a monopolistic
    lock-in on their music distribution channel (an example being the Motorola
    ROKR fiasco, which was so crippled by Apple-imposed restrictions that it was
    dead the moment it appeared), so Microsoft will totally control the premium-
    content distribution channel.  Not only will they be able to lock out any
    competitors, but because they will then represent the only available
    distribution channel they'll be able to dictate terms back to the content
    providers whose needs they are nominally serving in the same way that Apple
    has already dictated terms back to the music industry: Play by Apple's rules,
    or we won't carry your content. The result will be a technologically enforced
    monopoly that makes their current de-facto Windows monopoly seem like a velvet
    glove in comparison.

    Overall, Vista's content-protection functionality seems like an astonishingly
    short-sighted piece of engineering, concentrating entirely on content
    protection with no consideration given to the enormous repercussions of the
    measures employed.  It's something like the PC equivalent of the (hastily
    dropped) proposal mooted in Europe to put RFID tags into high-value banknotes
    as an anti-counterfeiting measure, completely ignoring the fact that the major
    users of this technology would end up being criminals who would use it to
    remotely identify the most lucrative robbery targets.

    The worst thing about all of this is that there's no escape.  Hardware
    manufacturers will have to drink the kool-aid (and the reference to mass
    suicide here is deliberate [Note D]) in order to work with Vista: "There is no
    requirement to sign the [content-protection] license; but without a
    certificate, no premium content will be passed to the driver".  Of course as a
    device manufacturer you can choose to opt out, if you don't mind your device
    only ever being able to display low-quality, fuzzy, blurry video and audio
    when premium content is present, while your competitors don't have this
    (artificially-created) problem.

    As a user, there is simply no escape.  Whether you use Windows Vista, Windows
    XP, Windows 95, Linux, FreeBSD, OS X, Solaris (on x86), or almost any other
    OS, Windows content protection will make your hardware more expensive, less
    reliable, more difficult to program for, more difficult to support, more
    vulnerable to hostile code, and with more compatibility problems.

    Here's an offer to Microsoft: If we, the consumers, promise to never, ever,
    ever buy a single HD-DVD or Blu-Ray disc containing any precious premium
    content [Note E], will you in exchange withhold this poison from the computer
    industry?  Please?


    This document was put together with input from various sources, including a
    number that requested that I keep their contributions anonymous (in some cases
    I've simplified or rewritten some details to ensure that the original,
    potentially traceable wording of non-public requirements docs isn't used).
    Because it wasn't always possible to go back to the sources and verify exact
    details, it's possible that there may be some inaccuracies present, which I'm
    sure I'll hear about fairly quickly.  No doubt Microsoft (who won't want a
    view of Vista as being broken by design to take root) will also provide their
    spin on the details.

    In addition to the material present here, I'd be interested in getting further
    input both from people at Microsoft involved in implementing the content
    protection measures and from device vendors who are required to implement the
    hardware and driver software measures.  I know from the Microsoft sources that
    contributed that many of them care deeply about providing the best possible
    audio/video user experience for Vista users and are quite distressed about
    having to spend time implementing large amounts of anti-functionality when
    it's already hard enough to get things running smoothly without the
    intentional crippling.  I'm always open to further input, and will keep all
    contributions confidential unless you give me permission to repeat something.
    If you want to encrypt things, my PGP key is linked from my home page,


    Because this writeup started out as a private discussion in email, a number of
    the sources used were non-public.  The best public sources that I know of are:

    "Output Content Protection and Windows Vista",, from WHDC.

    "Windows Longhorn Output Content Protection",,
    from WinHEC.

    "How to Implement Windows Vista Content Output Protection",,
    from WinHEC.

    "Protected Media Path and Driver Interoperability Requirements",,
    from WinHEC.

    An excellent analysis from one of the hardware vendors involved in this comes
    from ATI, in the form of "Digital Media Content Protection",,
    from WinHEC.  This points out (in the form of PowerPoint bullet-points) the
    manifold problems associated with Vista's content-protection measures, with
    repeated mention of increased development costs, degraded performance and the
    phrase "increased costs passed on to consumers" pervading the entire
    presentation like a mantra.

    (Note that the crypto requirements have changed since some of the information
    above was published, for example SHA-1 has been deprecated in favour of
    SHA-256 and SHA-512, and public keys seem to be uniformly set at 2048 bits in
    place of the mixture of 1024-bit and 2048-bit mentioned in the presentations).

    In addition there have been quite a few writeups on this (although not going
    into as much detail as this document) in magazines both online and in print,
    one example being PC World's feature article "Will your PC run Windows
    Vista?",, which covers this in the
    appropriately-titled section "Multimedia in chains".  Audience reactions at
    WinHEC are covered in "Longhorn: tough trail to PC digital media" published in
    EE Times (,
    unfortunately you need to be a subscriber to read this but you may be able to
    find accessible cached copies using your favourite search engine.


    Note A: I'll make a prediction at this point that, given that it's trying to
    do the impossible, the Vista content protection will take less than a day to
    bypass if the bypass mechanism is something like a driver bug or a simple
    security hole that applies only to one piece of code (and can therefore be
    quickly patched), and less than a week to comprehensively bypass in a
    driver/hardware-independent manner.  This doesn't mean it'll be broken the day
    or week that it appears, but simply that once a sufficiently skilled attacker
    is motivated to bypass the protection, it'll take them less than a day or a
    week to do so.

    Note B: I see some impressive class-action suits to follow if this revocation
    mechanism is ever applied.  Perhaps Microsoft or the content providers will
    buy everyone who owns a device that inadvertently leaks content and is then
    disabled by the revocation process replacement hardware for their system.
    Some contributors have commented that they can't see the revocation system
    ever being used because the consumer backlash would be too enormous, but then
    the legal backlash from not going ahead could be equally extreme.  For anyone
    who's read "Guns of August", the situation seems a bit like pre-WWI Europe
    with people sitting on step 1 of enormously complex battle plans that can't be
    backed out of once triggered, no matter how obvious it is that going ahead
    with them is a bad idea.  Driver revocation is a lose/lose situation for
    Microsoft, they're in for some serious pain whether they do or they don't.
    Their lawyers must have been asleep when they let themselves get painted into
    this particular corner.

    An entirely different DoS problem that applies more to HDMI-enabled devices in
    general has already surfaced in the form of, uhh, "DVI amplifiers", which take
    as input an HDMI signal and output a DVI signal, amplifying it in the process.
    Oh, and as a side-effect they just happen to remove the HDCP protection.
    These devices are relatively simple to design and build using off-the-shelf
    HDMI chips (I know of hardware hackers who have built their own protection-
    strippers using chip samples obtained from chip vendors.  If you have the
    right credentials you can even get hardware evaluation boards designed for
    testing and development that do this sort of thing).

    Now assume that the "DVI amplifier" manufacturer buys a truckload of HDMI
    chips (they'll want to get as many as they can in one go because they probably
    won't be able to go back and buy more when the chip vendor discovers what
    they're being used for).  Since this is a rogue device, it can be revoked...
    alongside hundreds of thousands or even millions of other consumer devices
    that use the same chip.  Engadget have a good overview of this scenario at

    Note C: We already have multiple reports from Vista reviewers of playback
    problems with video and audio content, with video frames dropped and audio
    stuttering even on high-end systems.  Time will tell whether this problem is
    due to immature drivers, or has been caused by the overhead imposed by Vista's
    content protection mechanisms interfering with playback.

    Note D: The "kool-aid" reference may be slightly unfamiliar to non-US readers,
    it's a reference to the 1978 Jonestown mass-suicide in which Jim Jones'
    followers drank Flavor Aid laced with poison in order to demonstrate their
    dedication to the cause.  In popular usage the term "kool-aid" is substituted
    for Flavor Aid because it has more brand recognition.

    Note E: If I do ever want to play back premium content, I'll wait a few years
    and then buy a $50 Chinese-made set-top player to do it, not a $1000 Windows
    PC.  It's somewhat bizarre that I have to go to Communist China in order to
    find vendors who actually understand the consumer's needs.

    A reductio ad absurdum solution to the "premium-content problem", proposed by
    a Slashdot reader, is to add support to Windows Vista for a black-box hardware
    component that accepts as input encrypted compressed premium content and
    produces as output encrypted (or otherwise protected) decoded premium content.
    In other words, move the entire mass of hardware, driver, and software
    protection into a dedicated black box that's only used in media PCs where it's
    (arguably) required.

    Now compare this add-on black box to the canonical Chinese-made $50 media
    player.  Why would anyone buy the black box (which will almost certainly cost
    more than $50) when they can buy a complete dedicated media player that does
    the same thing and more?

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