I was reading the thread about the different systems for buying Half Life 2 in the General Games forum today and noticed what might be the start to an interesting discussion, especially in a place where a good discussion IS possible (yay for the Highly Technical forum!).

Originally posted by 2630Goon in the General Games forum
In the future(not too far down the road)all content wether it be games or dvd movies or music cds will have to be purchased and downloaded off companies web sites.There will no longer be phsyical ways to copy a game or music cd.The companies will get rid of physical means of copying.Future dvd players and music cd players will not use a phsyical disk(music or dvd disk) at all, but movies or music will have to be downloaded from company sites to a hard drive device in the player itself.
The way I understand it, perfect copy protection is not possible. The data could be protected by encryption, but at some point the end user (also the cracker) would have to receive the key in order to use the data he/she bought a licence to.

If there is no way to decode the data then there are other ways to get to it too. In the case of software the code will eventually have to be run in a "naked" state in which it can be intercepted. In the case of audio/video the data must be in an interceptable state in order to reach the output device, or in the most extreme case of protection be interceptable between the output device and the viewer/listener.

As we all know, the copy protection only needs to be cracked once in order to make it useless.

What are some copy protection schemes that could provide "total protection"? How would you implement it? It seems like a very interesting (and on topic) engineering problem.