Some definitions
Conditional access
A means of ensuring that only those people who are supposed to have access to something do. This might be a username and password, or a smartcard, or something else.
Geographic restrictions
A form of conditional access which bases the decision upon where in the world you are. Can be implemented alone (as iPlayer does), or in tandem with other mechanisms (e.g., you must both be in the UK and have a valid subscription).
Protocol
The mechanism by which two devices (such as a TV and a set-top box, or a client and a server across the Internet) talk to each other. If a protocol is said to be open, then its specifications can be implemented by anybody. If all or part of the protocol is kept secret, then it’s not an open protocol.
DRM
A system for enforcing restrictions applied to content which you already have in your possession. DRM works by encrypting the content with a key known only to the “authorised” devices or software. In many cases, this encryption key is made up of two things: a sort of master key embedded in the software and a second key specific to the user (or device). Without the encryption key, the content is just a jumbled unplayable stream of data.
Because of this, the software capable of decrypting the content essentially has control over it. With DVDs and Blu-Ray discs, every official player is capable of decrypting the content, so you can take a disc and move it between players. Because those players don’t allow you to send the content over a network connection or USB port (and many will restrict the kinds of TVs they will play the content on), the players — and so the licensing agreement with the people who hand out the keys — is in control.
DVDs and Blu-Ray discs come “pre-DRM’d”. Some PVRs, on the other hand, encrypt some or all of content as they record it to disk, and again have control over what you can do with that content.
iTunes DRM on movies, TV shows and applications is transferrable. It works in concert with a server on the Internet, and once a computer or device has been authorised for your account, you can move content purchased or rented by that account between those devices. Once you “de-authorise” that device, you can no longer access the content. The “licensing” systems in some software programs (especially newer games) work in a similar way. In these cases, it’s essentially the remote server which is in control because it’s the one responsible for encrypting the content and distributing the keys on request.
