Digital Rights Management (DRM) is the name given to technologies that prevent someone from using a copyrighted digital work beyond the uses the copyright holder intends for it. Content companies believe such technology is necessary because they fear that once an unprotected copy of a digital work becomes available, it will be distributed over the Internet, and as a result, will lose its value.
One common approach to copy protection is encryption — the use of a mathematical/computational process to scramble information so that only those who have the right key or keys can obtain access to it. This, for example, is how your DVD movies work — their content is scrambled so that only DVD players that have the right keys can decrypt the content so that you can watch the DVD movie. Similarly, if you receive cable or satellite television, your TV service provider normally scrambles content in ways that prevent most unauthorized people (that is, nonsubscribers) from getting access to it.
The basic approach for encryption is to encrypt the digital content so that only a player with both the decryption device or software and the proper key can play the content. The content owner can broadcast the content to everyone but unless the recipient has valid decryption keys he cannot play the content. Scrambling is a similar copy-protection approach, but without a user-applied key; instead, the key that includes the unscrambling algorithm resides in the player device (which may be hardware, or software, or both).
The second approach to copy protection is something we can call “marking;” it depends on adding a mark in some way to the digital content. The mark may be used to indicate that the content is copyrighted, and in some cases it also carries instructions about what uses of the content are authorized. For example, in theory a mark may label some content as “do not copy” and another mark may label some other content as “copy once but don’t re-copy.”
There are three general forms a mark may take in the digital world. First, it may take the form of a simple label that is sent along with the content. Second, it may be a “watermark” — an arrangement of digital bits hidden in the background of the digital content. Or, third, it may be a “fingerprint” — a unique identifier that is derived from the characteristics of the content itself.
Marking is typically used for one of three reasons. First, it is used when an encryption-based method, for whatever reason, is not viable. For example, if the Federal Communications Commission requires that broadcast television signals not be encrypted — that they be broadcast “in the clear” — any DRM for broadcast television signals must be based on marking. Second, marking is used in systems that attempt to detect copying after the fact rather than preventing it — such use is among the so-called “forensic” uses of marking. Putting a mark on a piece of digital music, for example, allows one to create a search engine that can find a marked clip on the Internet, which the searcher might then assume is an unauthorized clip (on the theory that authorized marked clips aren’t available at all via the Internet). The third major use of marking is as a response to the so-called “analog hole.” The term “analog hole” refers to the ability of a would-be infringer to capture content as it is being played (or just before it is played). An example of this would be playing of a DVD and capturing the DVD’s content by using a camera with a microphone, or by replacing an output device such as a television set with a recording device, or by connecting to the digital player through analog connectors.
A third method is called “selective incompatibility. In this case, the manufacturer of a CD, for example, will add deliberate “errors” into encoding of music content on CDs, with the result that the CDs will be readable by some CD players (typically consumer-electronics single-purpose devices) and not by others (typically computer CD drives).
For a more full discussion of DRM, download the pdf “What Every Citizen Should Know about DRM, a.k.a. ‘Digital Rights Management’,” by Mike Godwin, Public Knowledge Legal Director.
