Jelton at Slashdot asks:

If digital media was available for sale at a reasonable price, but subject to a DRM scheme that allowed full legitimate usage (format shifting, time shifting, playback on different devices, etc.) and only blocked illicit usage (illegal copying), would you support the usage of such a DRM scheme? Especially if it meant a wealth of readily available compatible devices? In other words, if you object to DRM schemes, is your objection based on principled or practical concerns?

But this distinction doesn’t exist. Such perfect DRM is impossible, and we’ve known it is for decades. Perfect DRM would have to allow use of devices and technologies not yet conceived. It would have to allow all fair such devices, but no unfair devices. It would have to allow me to make a copy for backup, then make another after the first was destroyed—but we know it’s impossible to prove destruction of a copy.

Consider a program composed of three stages, A, B, and C, run in sequence. A does something legal. C does something illegal. Can the whole program run? It depends on whether B terminates. Perfect DRM has to solve the halting problem. There’s an equivalent proof using incompleteness.