Neal Stephenson - Cryptonomicon

As of the actual outbreak of war with Nippon, Schoen is on disability, and taking lots of drugs. Waterhouse spends as much time with Schoen as he is allowed to, because he's pretty sure that whatever happened inside of Schoen's head, between when the lists of apparently random numbers were dumped into his lap and when he finished building his machine, is an example of a noncomputable process.

Waterhouse's security clearance is upgraded about once a month, until it reaches the highest conceivable level (or so he thinks) which is Ultra/Magic. Ultra is what the Brits call the intelligence they get from having broken the German Enigma machine. Magic is what the Yanks call the intelligence they get from Indigo. In any case, Lawrence now gets to see the Ultra/Magic summaries, which are bound documents with dramatic, alternating red and black paragraphs printed on the front cover. Paragraph number three states:

NO ACTION IS TO BE TAKEN ON INFORMATION HEREIN REPORTED, REGARDLESS OF TEMPORARY ADVANTAGE, IF SUCH ACTION MIGHT HAVE THE EFFECT OF REVEALING THE EXISTENCE OF THE SOURCE TO THE ENEMY.

Seems clear enough, right? But Lawrence Pritchard Waterhouse is not so damn sure.

IF SUCH ACTION MIGHT HAVE THE EFFECT OF REVEALING…

At about the same time, Waterhouse has made a realization about himself. He has found that he works best when he is not horny, which is to say in the day or so following ejaculation. So as a part of his duty to the United States he has begun to spend a lot of time in whorehouses. But he can't have that much actual sex on what is still a glockenspiel player's pay and so he limits himself to what are euphemistically called massages.

ACTION… EFFECT… REVEALING…

The words stay with him like the clap. He lies on his back during these massages, arms crossed over his eyes, mumbling the words to himself. Something bothers him. He has learned that when something bothers him in this particular way it usually leads to his writing a new paper. But first he has to do a lot of hard mental pick-and-shovel work.

It all comes to him, explosively, during the Battle of Midway, while he and his comrades are spending twenty-four hours a day down among those ETC machines, decrypting Yamamoto's messages, telling Nimitz exactly where to find the Nip fleet.

What are the chances of Nimitz finding that fleet by accident? That's what Yamamoto must be asking himself.

It is all a question (oddly enough!) of information theory.

…ACTION…

What is an action? It might be anything. It might be something obvious like bombing a Nipponese military installation. Everyone would agree that this would constitute an action. But it might also be something like changing the course of an aircraft carrier by five degrees—or not doing so. Or having exactly the right package of forces off Midway to hammer the Nipponese invasion fleet. It could mean something much less dramatic, like canceling plans for an action. An action, in a certain sense, might even be the total absence of activity. Any of these might be rational responses, on the part of some commander, to INFORMATION HEREIN REPORTED. But any of them might be observable by the Nipponese—and hence any of them would impart information to the Nipponese. How good might those Nips be at abstracting information from a noisy channel? Do they have any Schoens?

…EFFECT…

So what if the Nips did observe it? What would the effect be exactly? And under what circumstances might the effect be REVEALING THE EXISTENCE OF THE SOURCE TO THE ENEMY?

If the action is one that could never have happened unless the Americans were breaking Indigo, then it will constitute proof, to the Nipponese, that the Americans have broken it. The existence of the source—the machine that Commander Schoen built—will be revealed.

Waterhouse trusts that no Americans will be that stupid. But what if it isn't that clear-cut? What if the action is one that would merely be really improbable unless the Americans were breaking the code? What if the Americans, in the long run, are just too damn lucky?

And how closely can you play that game? A pair of loaded dice that comes up sevens every time is detected in a few throws. A pair that comes up sevens only one percent more frequently than a straight pair is harder to detect—you have to throw the dice many more times in order for your opponent to prove anything.

If the Nips keep getting ambushed—if they keep finding their own ambushes spoiled—if their merchant ships happen to cross paths with American subs more often than pure probability would suggest—how long until they figure it out?

Waterhouse writes papers on the subject, keeps pestering people with them. Then, one day, Waterhouse receives a new set of orders.

The orders arrive encrypted into groups of five random-looking letters, printed out on the blue tissue paper that is used for top-secret cablegrams. The message has been encrypted in Washington using a one-time pad, which is a slow and awkward but, in theory, perfectly unbreakable cipher used for the most important messages. Waterhouse knows this because he is one of the only two persons in Pearl Harbor who has clearance to decrypt it. The other one is Commander Schoen, and he is under sedation today. The duty officer opens up the appropriate safe and gives him the one-time pad for the day, which is basically a piece of graph paper covered with numbers printed in groups of five. The numbers have been chosen by secretaries in a basement in Washington by shuffling cards or drawing chits out of a hat. They are pure noise. One copy of the pure noise is in Waterhouse's hands, and the other copy is used by the person who encrypted this message in Washington.

Waterhouse sits down and gets to work, subtracting noise from ciphertext to produce plaintext.

The first thing he sees is that this message's classification is not merely Top Secret, or even Ultra, but something entirely new: ULTRA MEGA.

The messages states that after thoroughly destroying this message, he—Lawrence Pritchard Waterhouse—is to proceed to London, England, by the fastest available means. All ships, trains, and airplanes, even submarines, will be made available to him. Though a member of the U.S. Navy, he is even to be provided with an extra uniform—an Army uniform—in case it simplifies matters for him.

The one thing he must never, ever do is place himself in a situation where he could be captured by the enemy. In this sense, the war is suddenly over for Lawrence Pritchard Waterhouse.

A network of chunnel-sized air ducts as vast and unfathomable as the global Internet ramifies through the thick walls and ceilings of the hotel and makes dim, attenuated noises that suggest that hidden deep within that system are jet engine proving grounds, Iron Age smithys, wretched prisoners draped with clanging chains, and writhing clumps of snakes. Randy knows that the system is not a closed loop—that it is somewhere connected to the earth's atmosphere—because faint street smells drift in from outside. For all he knows, they may take an hour to work their way into his room. After he has been living there for a couple of weeks, the smells come to function as an olfactory alarm clock. He sleeps to the smell of diesel exhaust because the traffic conditions of Manila require that the container ships load and unload only at night. Manila sprawls along a warm and placid bay that is an infinite reservoir of mugginess, and because the atmosphere is as thick and opaque and hot as a glass of milk straight from the cow's udder, it begins to glow when the sun rises. At this, Manila's regiments and divisions of fighting cocks, imprisoned in makeshift hutches on every rooftop, balcony and yard, begin to crow. The people come awake and begin to burn coal. Coal smoke is the smell that wakes Randy up.