Digital Signal Processing Reference
In-Depth Information
Fig. 8
License acquisition
for portable devices
License Server
Direct
License Acquisition
Direct
License Acquisition
Internet
Indirect
License Acquisition
Figure
8
shows that under Windows Media DRM portable devices can acquire
licenses either directly from a license server through an Internet connection, or
indirectly, from a local media server (for example a user's computer).
Figure
9
shows license acquisition scenarios when two devices support the
Windows Media DRM for Network devices. In this scenario, in addition to the
basic DLNA stack, the digital media receiver integrates the Windows Media DRM
layer (WMDRM) and has also the capability to play Windows Media Video (WMV)
content.
Using Windows Media DRM for network devices, the two devices exchange keys
and data as follows:
The first time a device is used it must be registered and authorized by the server
through UPnP. A special certificate identifies the device and contains information
used to ensure secure communication.
During the initial registration, the server performs a proximity detection to verify
that it is close enough to be considered inside the home.
Periodically, the server repeats the proximity detection to revalidate the device.
The device requests content for playback from the server.
If the server determines that the device is validated and has the right to play the
content, it sends a response containing a new, encrypted session key, a rights
policy statement specifying the security restrictions that the device must enforce,
and finally the content. The content is encrypted by the session key. Each time
content is requested, a new session is established.
The network device must parse the rights policy and determine if it can adhere to
the required rights. If it can, it may render the content.
As digital content is shared among multiple devices, most made by different
manufacturers, an open DRM standard or DRM-free content seem to be the only
ways to achieve inter-operability.
