Cryptonomicon

Randy's computer runs Finux, so when it boots up it gives him a black screen with big fat white letters scrolling up it one line at a time, a real circa-1975 type of user interface. Also presumably the easiest possible thing to read through Van Eck phreaking. Randy types in "startx" and the screen goes black for a moment and then turns a particular shade of indigo that Randy happens to like, and beige windows appear on it with much smaller and crisper black letters. So now he is running the X Windows System, or X as people like Randy call it, which provides all of the graphical junk that people expect in a user interface: menus, buttons, scroll bars, and so on. As with anything else under UNIX (of which Finux is a variant), there are a million options that only young, lonely, or obsessed people have the time and patience to explore. Randy has been all three at various times of his life and knows a lot about these options. For example, the background of his screen happens to be a uniform indigo at the moment, but it could be an image. Theoretically you could use a movie, so that all of your windows and menus and so on would float around on top of, say, Citizen Kanerunning in an endless loop. You can, in fact, take any piece of software and make it into your screen background, and it will purr along happily, doing whatever it does, and not even known that it's being used as window-dressing. This has given Randy some ideas on how to approach the Van Eck thing.

In its current state, this computer is just as vulnerable to Van Eck phreaking as it was before Randy started up X. Before it was white letters on a black background. Now it's black on beige. The letters are a little smaller and they live in windows, but it makes no difference: the electronics inside his computer still have to make these transitions between zero and one, i.e. between high intensity (white or beige) and minimal (black) as they trace out these patterns of dots on the screen.

Randy fundamentally does not know what the fuck is going on in his life right now, and probably hasn't for a long time, even back in the days when he thought that he didknow. But his working hypothesis is that the people who set this whole situation up (prime candidates: the Dentist and his cohorts in the Bolobolo syndicate) know that he has some cool information on his hard drive. How should they know this? Well, Pontifex--the Wizard--Enoch Root--whatever the fuck he's called--when he phoned Randy on the plane, knew that Randy had Arethusa, so God knows who else might know. Someone set up the fake drug bust at NAIA so that they could nab his laptop and yank the hard drive and make a copy of its contents. Then they found out that it was all doubly encrypted. That is, the Arethusa intercepts are encrypted to begin with in a pretty good World War II cryptosystem, which anyone should be able to break nowadays, but on top of that they are furthermore encrypted in a state-of-the-art modern system that no one can break. If they know what's good for them, they won't even try to break it. The only way for them to get the information is to get Randy to decrypt it for them, which he can do by biometrically identifying himself to his laptop (by talking to it) or by typing in a pass-phrase that only he knows. They are hoping that Randy will decrypt the Arethusa intercept files and, like a moron, display their contents on the screen. The moment that stuff appears on the screen, the game is over. The Dentist's (or whoever's) surveillance guys can feed the intercepts to some kind of a cryptanalytic supercomputer that will break them open in no time.

That doesn't mean that Randy dare not open those files--just that he daren't display them on the screen. This distinction is crucial. Ordo can read the encrypted files from the hard drive. It can write them into the computer's memory. It can decrypt them, and write the results into another region of the computer's memory, and leave that data there indefinitely, and the Van Eck phreakers will never be the wiser. But as soon as Randy tells the computer to show him that information in a window on the screen, the Arethusa intercepts will belong to the Van Eck phreakers; and whoever they are, they can probably break them faster than Randy can.

The fun and interesting thing is that Randy doesn't have to actually see those intercepts in order to work on them. As long as they are sitting in the computer's memory, he can subject them to every cryptanalystic technique in the whole Cryptonomicon.