TheProtected Media Path is a set of technologies creating a "Protected Environment," first included inMicrosoft'sWindows Vistaoperating system, that is used to enforcedigital rights management (DRM) protections on content.Its subsets areProtected Video Path (PVP) andProtected User Mode Audio (PUMA). Any application that uses Protected Media Path in Windows usesMedia Foundation.
The protected environment in which DRM content is played contains the media components that play DRM content, so the application only needs to provide remote control (play, rewind, pause, and so on), rather than having to handle unprotected content data. The protected environment also provides all the necessary support for Microsoft-approved (signed) third-party software modules to be added. It provides a "wall" against outside copying, where within the walls, content can be processed without making the content available to unapproved software.
In order to prevent users from copying DRM content, Windows Vista provides process isolation and continually monitors what kernel-mode software is loaded. If an unverified component is detected, then Vista will stop playing DRM content, rather than risk having the content copied. The protected environment is implemented completely in software, so software-based attacks such as patching the Windows kernel are possible.[1]
These restrictions concern the various outputs from the PC. For DRM content, digital outputs such asDigital Visual Interface (DVI) and High Definition Multimedia Interface (HDMI) will haveHigh-bandwidth Digital Content Protection (HDCP) enabled, to prevent someone from recording the digital stream. Even analog TV-style outputs typically require some restrictions, provided by mechanisms such asMacrovision andCGMS-A. These restrictions only apply to DRM-restricted content, such asHD DVD orBlu-ray that are encrypted withAACS, and also apply in Windows XP using supported playback applications.[2][3] Users' standard unprotected content will not have these restrictions. Some output types such asS/PDIF (Sony/Philips Digital Interchange Format) typically don't have a suitable DRM scheme available, so these need to be turned off reliably if the content so specifies.
In Vista, the control of PC video outputs is provided by PVP-OPM, which is essentially the next generation ofCertified Output Protection Protocol (COPP) introduced inWindows XP. However, rather than being a softwareapplication programming interface, PVP-OPM operates with the Windows media components in the protected environment.
Additionally,PVP-UAB (Protected Video Path - User-Accessible Bus) is used toencrypt video and audio data as it passes over thePCI-Expressbus, to prevent it from being intercepted and copied on the way to thegraphics card. It is complementary to PVP Output Protection Management.
In January 2007 the developerAlex Ionescu announced that he had found a method that allows end users to bypass Vista's Protected Media Path.This would allow digital content to be played on equipment that does not implement DRM restriction measures (like rescaling of video resolutions and disabling analog audio outputs).However, he did not release any source code in fear of a Microsoft lawsuit regarding possible violation of theDMCA.[4] On 6 March 2007, Microsoft responded after internal testing that the described method would not work.[5]
In addition to common criticisms against DRM schemes, there has been speculation that this scheme has been motivated by the fact that it would affect officialfree/open source graphics driver support by manufacturers. The scheme relies on the internals ofgraphics cards to tell whether the hardware is trustworthy (permitted to play copy-protected content). This could be subverted if an attacker knows certain details about the hardware's operation, which could be disclosed by hardwaredocumentation or open sourcedevice drivers.[6] However, this will not affect platform independency, as the scheme is provided with no charge.[7]
Microsoft has frequently been accused of adding the Protected Media Path feature to Vista to block customers from copying rightfully owned media content[8] (a practice believed to be protected by Fair Use provisions of the Copyright Act), and the feature is widely quoted as an example of Microsoft's uncompromising adherence to DRM.
These accusations have never gained much traction[citation needed] largely because Vista treats non-DRM media exactly the same as previous versions of Windows, and that following Vista's release there has been no change in the availability of free/open source drivers from graphics hardware manufacturers.[citation needed]
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