Anyhow: it still is possible to get access to these documents if the government gives him sufficient immunity, as the court notes. This would be pretty important because if no one could ever access these documents (which presumably would be possible if the would-be defendant doesn't decrypt them) that would be an enormous problem for our justice system.

Here's the sticking point for me: it's perhaps overly pedantic, but I want to view the world honestly, and there are some great points of absurdity here. (I always like the absurd, and the ways our world is otherworldly.)

The problem is that much of our approach to information is creative, and we need to start thinking in those terms.

If you have a JPEG of a murder on your unencrypted hard drive, that's not actually a photograph; it's a set of magnetic pointings which can with certain hardware be used to produce a photograph. If you think about it, that also applies to writing on paper, or colored splotches encoding an image into a physical photograph. Those require a creative attempt to produce meaning. The meaning can be off if the creative attempt is not followed through correctly. The easy way to see this is to imagine someone systematically using a common word in an uncommon way -- Feynman for example was once, on the Challenger commission, chasing down memos which sounded like NASA had been actively irresponsible, but instead it turned out to be a figure of speech they'd adopted for a certain phase of their construction. Or imagine that our demented individual really does have a very detailed, lifelike photograph which appears to document his murder of another, but in fact the "murdered" girl is a still-alive actress who was paid to appear in these photographs; the "blood" and such is very convincing but is ultimately a prop.

So the meaning can be off, if the creative act goes awry. I'm using this to underscore that you have to think, at some level, about that recreation of semantics from the physical fact.

Let me be clear: I don't think this is a barrier to investigation usually. I think it's clear that we expect a sort of 'normal hardware' that allows us to recreate semantics. The photographs in this safe, when viewed by a normal person in normal lighting, would show an image of the defendant committing a murder -- and if they want to say that this was all theatrically staged, they may produce the actress or others involved in the production. By that account, photographs inside of a safe are also governed by this principle: even if their physical location happens to be remote and inaccessible, reproducing the image from the photograph is as simple as just looking at it. The photograph really contains the image, up to a 'trivial' semantics.

Now bring this back to your other example of an encrypted disk storing child pornography. That is a nontrivial semantic inflation: you are literally asking the defendant to create child pornography for the purposes of the case. In some sense perhaps you're just saying "create whatever this drive's contents are," with the understanding that the police is going to look through it for child pornography -- in that phrasing, it's more clear that this pornography might not actually exist, etc. -- so there is perhaps a way to comply without generating child pornography at the judge's request.

But still, that's a little mad and absurd in the wonderful way that our world can be otherworldly. It opens up all sorts of questions which I have no clue how to answer. Decryption, like most computation, is a creative act. To demand decryption is to demand creation.

I quoted the above in particular because I really don't care about the "enormous problem for our justice system." Like, the fact that we don't have embedded realtime GPS trackers installed in our spines is an "enormous problem for our justice system" because it makes it so tremendously hard to figure out whether our alibis are true or false. Screw that sort of thinking. Whatever caused the investigators to think this individual was manufacturing or downloading kiddie porn should have been enough to convict. This shouldn't be a gray-matter area. "We just cracked down on this peer-to-peer kiddie porn program, we saw that you were using it to share many images, here are the filenames that the defendant's computer was sharing at the time we busted into his house with a warrant." (Are the police allowed to download such things? Probably. "Here are just a couple of the images we downloaded from him," too, then.) So, if they don't have a case and are fishing through the hard drive to try to make one, that's more or less explicitly what the Fifth Amendment is supposed to guard against: "we don't know your exact sins but we know you're a sinner so damn it, confess!"

But still, the sticking point is the glorious absurdity: "Mr. Doe, we have reason to believe that if you say the magic word, your computer will manufacture child pornography. We demand that you say the magic word, so that we know whether this is true." How will we decide that issue in the face of its pure and present absurdity?