Copy protection is a product of the information age. In order to understand why copy protection came about, let us examine a couple of different scenarios:
As an example, say I am an engineer and I spend a few years designing a super new car, the TMJ Zoomwhanger 3000. With significant investment, I build a factory to sell my Zoomwhangers. Once production is up and running, I can sell my Zoomwhangers to consumers. Every time a consumer buys a Zoomwhanger, I get the profits. This is my reward for my hard work in designing the car and my investment in the factory.
What if a rival car manufacturer were to start building and selling Zoomwhangers in their own factory? This would be unfair on me since they'd be benefiting from my work designing the car. Fortunately, I will have taken out all sorts of patents on the Zoomwhanger design and registered copyright on the Zoomwhanger name. It would be straightforward to have the rival manufacturer legally shut down.
What if an individual were to attempt to build a Zoomwhanger in their garage? This really isn't a problem for me, since it would be totally impractical for anyone to try this. Even if they could somehow get hold of the necessary tools, they would not benefit from economies of scale on the materials they'd need, and it would probably cost them more to build the car than to buy one from me. There is no need for any specific 'copy protection' mechanism - the Zoomwhanger is already sufficiently difficult to copy.
Now That's What I Call TMJ
Another scenario. Say I decide to publish a CD of my (ahem) wicked tracks. I painstakingly mix and record my album, 'Now That's What I Call TMJ', and through a deal with a record label, it is published.
Every time someone buys a copy of 'Now TMJ', I get some of the profits. This is my reward for my creative effort in recording the music.
As before, a rival record label would not be able to publish their own 'Now TMJ' CDs because it would be easy for me to legally shut them down if they did so.
However, it is nowadays trivially simple for any computer owner with a CD burner to make a perfect copy of 'Now TMJ'. What does this mean? Well, any time someone makes a copy of 'Now TMJ' for a friend, then there is virtually no chance of me selling them one of my own copies. I lose potential sales. Also, the people with the home-copied CDs are gleaning enjoyment from my creative talent without paying me, which may or may not bother me.
It's almost impossible for me to put a stop to this. Everyone who copies the CD has infringed my copyright, but to prosecute them I would have to take all to court individually. It can't possibly be worthwhile for me to prosecute, and because everyone knows this, there is no deterrent to stop people copying the CDs.
Implementing Copy Protection
Since I can't use the law to prevent people copying 'Now TMJ', my next step is to try to make it physically impossible for people to copy my CD. I attempt copy protection.
I need to alter the CD in some way. I have two goals here:
People who buy my CD must still be able to listen to the music on it
It must be impossible for someone to make a copy of my CD
The problem is, how can I possibly achieve this? The content of the CD is, in essence, information
. It's a particular series of 1s and 0s that makes up a digital version of my music.
In order for the CD to be any use, it needs to be possible for a CD player to play the CD. The way the CD player does that is by reading the information on the disc, and converting it into music. The thing is, reading the information on the disc is also the first stage of copying the disc.
Once the information on the disc has been read, I have no control over it any more. I don't know if it's been read for the purpose of listening to it or for the purpose of copying it. That's the fundamental problem.
Theoretically, if I had control over every single device that could read CDs, I could insist that only CD players (as opposed to any device that could copy the CD) would read it. In essence, this is what the creators of DVD tried to do with CSS. CSS encrypted the contents of the DVD. DVD makers had control over distribution of the keys to unlock the content. In practice, this failed rather dramatically. (Read about it under DeCSS).
In the digital age, it is not realistically possible to distribute information in such a way that it cannot be duplicated. Any copy protection method must ultimately be doomed to fail.