Windows Media DRM 10 for Portable Devices

For subscription or rental services, content owners want to be able to issue time-sensitive content licenses that are set to expire after a certain time period, rendering that content unusable unless consumers pay a periodic subscription fee. Most important, these licenses must remain attached to the content as it passes among devices, so that if the user does not pay the subscription fee, the content becomes useless on all the user’s devices.

Windows Media DRM 10 for Portable Devices (often known by its code name, Janus) addresses this problem with the following features:

On-board clocks. Devices that support Janus have a software-based clock so they can determine when the license for a particular content file has expired. Devices can notify users that their licenses will expire in a certain time (say, 24 hours).

License chaining. Content services can create “root” licenses that contain DRM information applicable to multiple pieces of content from the same content owner, such as how long a set of songs can be played before the license must be renewed. The license clearinghouse distributes this root license to the user’s PC, where it can then be used to create “leaf” licenses for individual items of content on the PC and portable devices. When a subscription expires, only the root license need be updated over the Internet, saving considerable time and reducing the load on license clearinghouses.