Friday, November 6, 2009

Moto perpetuo

It occurs to me that unbreakable copy protection is the perpetual motion of our day.

Back at the beginnings of the industrial revolution, when inventions like the steam engine and electrical generator were making new and mysterious things possible and were not widely understood, people were constantly coming up with perpetual motion schemes. And why not? If you can generate more power than hundreds of strong men and horses can produce just by burning coal, and transmit that power miles and miles away with simple metal wires, is it so implausible that some arrangement of magnets and overbalanced wheels could generate endless power from nothing?

Eventually, in the early 1800s, after commercial steam power had been around for about a century, the principle of conservation of energy came to be widely accepted and by the the middle of the century the familiar laws of thermodynamics were established, including the crucial first two:
  1. You can't win (conservation of energy).
  2. You can't break even (entropy increases in a closed system).
These two principles explain why perpetual motion schemes don't work. That hasn't stopped people from coming up with them, but it has stopped knowledgeable engineers and scientists from wasting time on them. It hasn't completely stopped investors from investing in them, but the long and sorry track record of such schemes probably has been a deterrent.

Why do people still bother, then? Because if it were possible, large-scale perpetual motion would do away with energy shortages forever. It woudn't necessarily make any money, infinite supply implying zero price, and an energy surplus would have drawbacks of its own, but we could probably deal with those problems when they came up. The point is that people try to prove that perpetual motion is possible because they really, really want it to be.

Anyone in the business of selling information would really, really like to be able to control the propagation of that information. You do the math.

I don't know of any specific principle of information theory that explains why this will never work, but there's a growing body of empirical evidence to that effect. Intuitively, copying bits costs much less than the price sellers would like to charge, so the protection has to come in the conversion of those bits into usable form. That runs you right in to the analog reconversion problem, of which "camming" (sneaking cameras into movie theaters) is a crude but effective example.

Clearly none of this is currently stopping people from trying to come up with copy protection schemes, or people from paying for them. The track record probably isn't quite long or sorry enough yet. I suspect it eventually will be.

Fortunately, selling bits and making them impossible to copy are two different things.

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