How do technological protection measures work?
In general, right holders seek to control the use of their works in the online environment by utilizing specialized technologies. Technological protection measures take various forms and their features are continually changing.
These measures can broadly be grouped into two categories: first, measures that are deployed to limit access to protected content to users who are authorized to such access. Common access control features are, for example, cryptography, passwords, and digital signatures that secure the access to information and protected content.
The second major group of technologies aims at controlling the use of protected content once users have access to the work. According to the corresponding license agreement, certain uses of protected content may be allowed for certain purposes. To make sure that these obligations are complied with and no unauthorized reproductions are made, the respective technological measures attempt to track and control copying, and thus prevent the user from surpassing the right he has been granted. Examples of such copy control measures are serial copy management systems for audio digital taping devices, and scrambling systems for DVDs that prevent third parties from reproducing content without authorization.