Most people don’t have a problem with the concept that artists should be compensated for their work. DRM systems address this issue, using encryption for copy protection and license management systems to control how files may be used.
A simple DRM system verifies that your computer or portable player is authorized to play each song that you attempt to play. Beyond that, each music store can configure its DRM system to apply a set of rules that limit what you can do with any music purchased from them. These rules are normally determined by negotiation with the labels who own rights to the music.
Typical rules might limit the number of computers on which songs can be played, whether songs can be burned to a CD, and the number of times the same playlist of songs can be burned to a CD. Other rules can be added to limit the number of times you can play a song before you must purchase it, as in the case of the Weedshare “try before you buy” system covered later in this chapter.
Components of the DRM system are embedded in each file, while other components exist in the software and hardware used to play the music and on servers that maintain databases of licenses and rules.
Following are descriptions of Microsoft’s DRM system for WMA and Apple’s Fairplay DRM system for iTunes.
The first time you play a protected WMA file, your player software must access an online database to validate the license and store the information ...