Cryptonomicon

probably deciphered within hours. But he's not doing it for the war effort per se, just trying to keep his mind sharp and maybe add a few leaves to the next edition of the Cryptonomicon.When he arrives at Bletchley, which is his destination of the moment, he will have to ask around and find out what those messages actually said.

Usually, he is above such cheating. But the messages from U-553 have him completely baffled. They were not produced on an Enigma machine, but they are at least that difficult to decrypt. He does not even know, yet, what kind of cipher he is dealing with. Normally, one begins by figuring out, based on certain patterns in the ciphertext, whether it is, for example, a substitution or a transposition system, and then further classifying it into, say, an aperiodic transposition cipher in which keying units of constant length encipher plaintext groups of variable length, or vice versa. Once you have classified the algorithm, you know how to go about breaking the code.

Waterhouse hasn't even gotten that far. He now strongly suspects that the messages were produced using a one-time pad. If so, not even Bletchley Park will be able to break them, unless they have somehow obtained a copy of the pad. He is half-hoping that they will tell him that this is the case so that he can stop ramming his head against this particular stone wall.

In a way, this would raise even more questions than it would answer. The Triton four-wheel naval Enigma was supposedly considered by the Germans to be perfectly impregnable to cryptanalysis. If that was the case, then why was the skipper of U-553 employing his own private system for certain messages?

The locomotive starts hissing and sputtering like the House of Lords as Inner Qwghlmians emerge from the terminal building and take their seats on the train. A gaffer comes through the car, selling yesterday's newspapers, cigarettes, candy, and Waterhouse purchases some of each.

The train is just beginning to jerk forward when Waterhouse's eye falls on the lead headline of yesterday's newspaper: YAMAMOTO'S PLANE SHOT DOWN IN PACIFIC-ARCHITECT OF PEARL HARBOR THOUGHT TO BE DEAD.

'Malaria, here I come,' Waterhouse mumbles to himself. Then, before reading any further, he sets the newspaper down and opens up his pack of cigarettes. This is going to take a lot of cigarettes.

* * *

One day, and a whole lot of tar and nicotine later, Waterhouse climbs off the train and walks out the front door of Bletchley Depot into a dazzling spring day. The flowers in front of the station are blooming, a warm southern breeze is blowing, and Waterhouse almost cannot bear to cross the road and enter some windowless hut in the belly of Bletchley Park. He does it anyway and is informed that he has no duties at the moment.

After visiting a few other huts on other business, he turns north and walks three miles to the hamlet of Shenley Brook End and goes into the Crown Inn, where the proprietress, Mrs. Ramshaw, has, during these last three and a half years, made a tidy business out of looking after stray, homeless Cambridge mathematicians.

Dr. Alan Mathison Turing is seated at a table by a window, sprawled across two or three chairs in what looks like a very awkward pose but which Waterhouse feels sure is eminently practical. A full pint of some thing reddish brown is on the table next to him; Alan is too busy to drink it. The smoke from Alan's cigarette reveals a prism of sunlight coming through the window, centered in which is a mighty Book. Alan is holding the book with one hand. The palm of his other hand is pressed against his forehead, as if he could get the data from book to brain through some kind of direct transference. His fingers curl up into the air and a cigarette projects from between them, ashes dangling perilously over his dark hair. His eyes are frozen in place, not scanning the page, and their focus point is somewhere in the remote distance.

'Designing another Machine, Dr. Turing?'

The, eyes finally begin to move, and swivel around towards the sound of the visitor's voice. 'Lawrence,' Alan says once, quietly, identifying the face. Then, once more warmly: 'Lawrence!' He scrambles to his feet, as energetic as ever, and steps forward to shake hands. 'Delighted to see you!'

'Good to see you, Alan,' Waterhouse says. 'Welcome back.' He is, as always, pleasantly surprised by Alan's keenness, the intensity and purity of his reactions to things.

He is also touched by Alan's frank and sincere affection for him. Alan did not give this easily or lightly, but when he decided to make Waterhouse his friend, he did so in a way that is unfettered by either American or heterosexual concepts of manly bearing. 'Did you walk the entire distance from Bletchley? Mrs. Ramshaw, refreshment!'

'Heck, it's only three miles,' Waterhouse says.

'Please come and join me,' Alan says. Then he stops, frowns, and looks at him quizzically. 'How on earth did you guess I was designing another machine? Simply a guess based on prior observations?'

'Your choice of reading material,' Waterhouse says, and points to Alan's book: RCA Radio Tube Manual.

Alan gets a wild look. 'This has been my constant companion,' he says. 'You must learn about these valves, Lawrence! Or tubes as you would call them. Your education is incomplete otherwise. I cannot believe the number of years I wasted on sprockets!God!'

'Your zeta-function machine? I thought it was beautiful,' Lawrence says.

'So are many things that belong in a museum,'Alan says.

'That was six years ago. You had to work with the available technology,' Lawrence says.

'Oh, Lawrence! I'm surprised at you! If it will take tenyears to make the machine with availabletechnology, and only fiveyears to make it with a newtechnology, and it will only take twoyears to inventthe new technology, then you can do it in sevenyears by inventing the new technology first!'

'Touche'

'This is the new technology,' Alan says, holding up the RCA Radio Tube Manuallike Moses brandishing a Tablet of the Law. 'If I had only had the presence of mind to use these, I could have built the zeta-function machine much sooner, and others besides.'

'What sort of a machine are you designing now?' Lawrence asks.

'I've been playing chess with a fellow named Donald Michie-a classicist,' Alan says. 'I am wretched at it. But man has always constructed tools to extend his powers-why not a machine that will help me play chess?'

'Does Donald Michie get to have one, too?'

'He can design his own machine!' Alan says indignantly.

Lawrence looks carefully around the pub. They are the only customers, and he cannot bring himself to believe that Mrs. Ramshaw is a spy. 'I thought it might have something to do with-' he says, and nods in the direction of Bletchley Park.

'They are building-I have helped them build-a machine called Colossus.'

'I thought I saw your hand in it.'

'It is built from old ideas-ideas we talked about in New Jersey, years ago,' Alan says. Brisk and dismissive is his tone, gloomy is his face. He is hugging the RCA Radio Tube Manualto himself with one arm, doodling in a notebook with the other. Waterhouse thinks that really the RCA Radio Tube Manualis like a ball and chain holding Alan back. If he would just work with pure ideas like a proper mathematician he could go as fast as thought. As it happens, Alan has become fascinated by the incarnations of pure ideas in the physical world. The underlying math of the universe is like the light streaming in through the window. Alan is not satisfied with merely knowing that it streams in. He blows smoke into the air to make the light visible. He sits in meadows gazing at pine cones and flowers, tracing the mathematical patterns in their structure, and he dreams about electron winds blowing over the glowing filaments and screens of radio tubes, and, in their surges and eddies, capturing something of what is going on in his own brain. Turing is neither a mortal nor a god. He is Antaeus. That he bridges the mathematical and physical worlds is his strength and his weakness.

'Why are you so glum?' Alan says. 'What have you been working on?'

'Same stuff, different context,' Waterhouse says. With these four words he conveys, in full, everything that he has been doing on behalf of the war effort. 'Fortunately, I came upon something that is actually rather interesting.'

Alan looks delighted and fascinated to hear this news, as if the world had been completely devoid of