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Architecture of Windows Media Rights Manager

Contents

Introduction

When a consumer acquires an encrypted digital media file from a Web site, he or she must also acquire a license that contains a key to unlock the file before the content can be played. Content owners can easily set these licenses and keys in motion by protecting their content files with Microsoft® Windows Media® Rights Manager and then distributing the content to consumers.

The following illustration shows how content is protected, distributed, and used with Windows Media Rights Manager:

Windows Media Rights Manager Flow

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How Windows Media Rights Manager Works

Windows Media Rights Manager lets content providers deliver songs, videos, and other digital media content over the Internet in a protected, encrypted file format. Windows Media Rights Manager helps protect digital media (such as songs and videos) by packaging digital media files. A packaged media file contains a version of a media file that has been encrypted and locked with a "key." This packaged file is also bundled with additional information from the content provider. The result is a packaged media file that can only be played by a person who has obtained a license.

The basic Windows Media Rights Manager process is as follows:

Packaging
Windows Media Rights Manager packages the digital media file. The packaged media file has been encrypted and locked with a "key." This key is stored in an encrypted license, which is distributed separately. Other information is added to the media file, such as the URL where the license can be acquired. This packaged digital media file is saved in Windows Media Audio format (with a .wma file name extension) or Windows Media Video format (with a .wmv file name extension).
Distribution
The packaged file can be placed on a Web site for download, placed on a media server for streaming, distributed on a CD, or e-mailed to consumers. Windows Media Rights Manager permits consumers to send copy-protected digital media files to their friends, as well.
Establishing a License Server
The content provider chooses a license clearing house that stores the specific rights or rules of the license and implements the Windows Media Rights Manager license services. The role of the clearing house is to authenticate the consumer's request for a license. Digital media files and licenses are distributed and stored separately, making it easier to manage the entire system.
License Acquisition
To play a packaged digital media file, the consumer must first acquire a license key to unlock the file. The process of acquiring a license begins automatically when the consumer attempts to acquire the protected content, acquires a predelivered license, or plays the file for the first time. Windows Media Rights Manager either sends the consumer to a registration page where information is requested or payment is required, or "silently" retrieves a license from a clearing house.
Playing the Media File
To play the digital media file, the consumer needs a media player that supports Windows Media Rights Manager. The consumer can then play the digital media file according to the rules or rights that are included in the license. Licenses can have different rights, such as start times and dates, duration, and counted operations. For instance, default rights may allow the consumer to play the digital media file on a specific computer and copy the file to a portable device. Licenses, however, are not transferable. If a consumer sends a packaged digital media file to a friend, this friend must acquire his or her own license to play the file. This PC-by-PC licensing scheme ensures that the packaged digital media file can only be played by the computer that has been granted the license key for that file.

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How Keys Work

The content owner locks their content with a "key" to create a packaged file. Before the consumer can play the file, the license clearing house creates a license containing the key that can unlock the packaged file and download the license to the consumers PC. The following diagram shows how keys are created and used in Windows Media Rights Manager.
Windows Media Rights Manager Licenses

To generate a key, a license key seed and a key ID are needed:

The license key seed is a value that is known only to the content owner and license clearing house.
The key ID is created by the content owner for each Windows Media file. This value is included in the packaged file.

When the license clearing house needs to issue a license for a packaged file, a key can be recreated by retrieving the key ID from the packaged file. The Windows Media License Service uses the license key seed (which the clearing house provides) and the key ID from the packaged file to create a key. The key is included in the license sent to the consumer's computer. Using the key included in the license, the player on the consumer's computer can open and play the protected file.

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How Licenses Work

Each license contains the key to unlock the Windows Media file. The license also contains the rights, or rules, that govern the use of the digital media file. The content owner sets these rights to determine which actions are allowed from minimal control over playback to more restrictive licenses. The licenses in Windows Media Rights Manager can support a wide range of different business rules, including:

How many times can a file be played.
Which devices a file can be played or transferred on. For example, rights can specify if consumers can transfer the file to portable devices that are compliant with the Secure Digital Music Initiative (SDMI).
When the user can start playing the file and what is the expiration date.
If the file can be transferred to a CD recorder (burner).
If the user can back up and restore the license.
What security level is required on the client to play the Windows Media file.
And many others.

Licenses can be delivered in different ways and at different times, depending on the business model. The content owner might want licenses pre-delivered, or they might want the license delivered after a consumer has downloaded and attempted to play a packaged file for the first time. Licenses can be delivered with or without the consumer being aware of the process using silent or non-silent license delivery.