In the same way as with video, the PCIe bus could become a problem for premium audio, because content owners might regard it as a user-accessible bus. The issue affects the use of a discrete audio card or a discrete graphics card that has audio capabilities. While there might not be many discrete audio cards in 2006, there more than likely will be HDMI discrete graphics cards that have HD Audio controllers.
The important scenario is the play back of HD-DVDs and Blu-Ray DVDs. In this case, the video is considered premium and the audio may also be. There is no problem with the video, because PVP-UAB protects the video over the PCIe bus, but there is currently no equivalent protection available in the audio world.
The PCIe bus may be defined in some Content Industry Agreements as a user-accessible bus. It is further defined in some Content Industry Agreements that premium audio is not allowed to pass over a user-accessible bus in unprotected form. In spite of PC industry push-back on this requirement, it is not certain which way the decision will fall. Realistically, any concession in this area would only be valid for a small number of years, so the PC industry needs to address this issue in the not-too-distant future. Microsoft plans to address this as part of the PAP project that will be a number of years after the initial release of Windows Vista.
When the PC industry does PAP, there will be a way of encrypting audio over the PCIe bus. For discrete graphics manufacturers, the easiest mechanism to use would be PVP, because their graphics chip hardware will already be able to decrypt this. The encryption would be done in an Output Encryption APO module in the Audio Engine in the Protected Environment.
As mentioned earlier, the plan is to provide a mechanism in Windows Vista to load a future Output Encryption APO module. Even in the initial version of Windows Vista, however, a third party could write a custom Output Encryption APO module that performs PVP encryption. This would need to establish a separate session key, because there is no robust way of getting the session key from the graphics stack to the audio stack.
We hope to be successful with the amendment to the content industry agreements, so that using an encrypting Output Encryption APO module can be deferred for a few years.
PUMA Summary
The requirement for audio output content protection is just beginning to become important.
The experience with SAP influenced the plans for Windows Vista. It might be that the content owners do decide to turn on SAP in the coming year, but even that is not certain. Microsoft provides the protection tools, but it is up to the content owners to turn them on if they are needed.
For 2006–2008, and possibly beyond, Microsoft is providing what is believed to be a suitable set of audio output content protection tools for the content owners to use. Windows Vista provides an architecture that will allow the ability to add protection tools if they become necessary.
The use of HFS authentication of hardware, as used in PVP, is on the list of possible future additions. Bus encryption may also be important in the future, but there is no particular hurry.
Watermark detection is high on content owners’ agenda, but there are lots of issues with it. There are complex technical issues, business issues, and consumer issues.
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