Microsoft recently released its beta version of Windows Media Player 9, complete with its new Digital Rights Management (DRM) system. LawMeme takes a look at how Microsoft's DRM system functions.
Microsoft's DRM system has three basic goals: to protect, distribute, and sell digital media with confidence, to develop flexible business models that maximize revenues and reduce costs, and to reach a wide audience of customers with secure digital music and video.
The process of producing and distributing DRM media begins with the encoding of the original media, or packaging. Packaging begins by taking the original media, encrypting it, and locking it with a key. Specifically, a license key seed and key id are generated by the content creator. The license key seed that is used to lock the file is stored in an encrypted license file, which is distributed independently of the encrypted media file. The license key seed is known only to the content creator and license distributor. The encrypted media file also contains some metadata, such as the URL where the license file may be obtained and, more importantly, the key id for the packaged file. This key id will be used in requesting a license from the license server. Our media file is then saved in either a Windows Media Audio format or a Windows Media Video format.
Once a media file has been encrypted and locked with a license key seed and contains the key id, it is ready for distribution. Distribution can occur by several methods including downloading the encrypted file from a URL, streaming the media from a media server, receiving the media on CD, or obtaining the media by way of e-mail. An interesting feature of Windows DRM is that these files may be freely e-mailed from one user to another. However, each user will still need a separate license to actually play the media if the license is non-transferable.
Before a user can play the encrypted media, he/she must be able to download the appropriate license key. In order to do this, a license key server must be established, either by the entity that created the encrypted media or a separate entity that specializes in license servers. The role of the license server is to authenticate the user's request for a license. Remember, licenses and media are distributed separately.
Assuming that a license server exists, a user can request a license to play the media. When a user first plays the media, Windows Media Player determines whether he/she has a license to play the media. If the user does not, there are several methods of obtaining a license. A license is obtained by sending the license server information about the client that is requesting the license and the media for which the license is needed. The license server then takes the license key seed for the media and the key id to produce a license file with a third key. The third key is then used to grant access to the licensed media. The first method of obtaining a license, called the "silent" method, is the simplest. Windows Media Player simply contacts the license server and retrieves the license key. The user is usually unaware that this is even happening since no user action, such as the submission of personal information, is required. This may also be used with subscription style services. The "non-silent" method requires some user action before he/she is able to access the protected content. After the user performs the requested action, the user will be able to obtain a valid license. The third type of license delivery is the "non-pre-delivered" method. This is the method by which content is super-distributed and acquiring a license comes after the content has been distributed. No action on behalf of the user is required to obtain the media other than a trivial download, received email, etc. The last method is called "license pre-delivered." This is the case where the license is delivered at the time of purchase of the media.
Requesting a license also requires that "client information" be sent to the license server, such as a hardware id. This ensures that the license is only valid for the machine that requests it. Therefore, transferring your media to your portable player may not be permitted if the content owner does not wish. Users may be required to obtain a different license to play their media on portable devices.
Once the license key has been received, a user can play the encrypted media. However, the user is restricted by "rules" and "rights." Licenses can have different rights, such as limiting the amount of time that the media can be played, the number of times that it may be played, or even a date range of acceptable use. Furthermore, rights and rules can dictate whether or not media may be transferred to a portable device. Licenses are non-transferable. Sending an encrypted media file to a friend that a user has rights to will require that the friend obtain a separate license.