Cryptonomicon

"I knew perfectly well that only a handful of people in the world had the acumen to break the Enigma and then to cover up the fact that they had broken it. By using our intelligence sources to ascertain where these men were, and what they were doing, I could make inferences." Von Hacklheber stubs out his cigarette, sits up straight, and drains a half-shot of schnapps, warming to the task. "This was a human intelligence problem--not signals intelligence. This is handled by a different branch of the service--" and he's off again talking about the structure of the German bureaucracy. Terrified, Shaftoe flees from the room, runs outside, and uses the outhouse. When he gets back, von Hacklheber is just winding up. "It all came down to a problem of sifting through large amounts of raw data--lengthy and tedious work."

Shaftoe cringes, wondering what something would have to be like in order to qualify as lengthy and tedious to this joker.

"After some time," von Hacklheber continues, "I learned, through some of our agents in the British Isles, that a man matching the general description of Lawrence Pritchard Waterhouse had been stationed to a castle in Outer Qwghlm. I was able to arrange for a young lady to place this man under the closest possible surveillance," he says dryly. "His security precautions were impeccable, and so we learned nothing directly. In fact, it is quite likely that he knew that the young woman in question was an agent, and so took added precautions. But we did learn that this man communicated through one-time pads. He would read his encrypted messages over the telephone to a nearby naval base whence they would be telegraphed to a station in Buckinghamshire, which would respond to him with messages encrypted using the same system of one-time pads. By going through the records of our various radio intercept stations we were able to accumulate a stack of messages that had been sent by this mysterious unit, using this series of one-time pads, over a period of time beginning in the middle of 1942 and continuing up to the present day. It was interesting to note that this unit operated in a variety of places:

Malta, Alexandria, Morocco, Norway, and various ships at sea. Extremely unusual. I was very interested in this mysterious unit and so I began trying to break their special code."

"Isn't that impossible?" Bischoff asks. "There is no way to break a one-time pad, short of stealing a copy."

"That is true in theory," von Hacklheber says. "In practice, this is only true if the letters that make up the one-time pad are chosen perfectly randomly. But, as I discovered, this is not true of the one-time pads used by Detachment 2702--which is the mysterious unit that Waterhouse, Turing, and these two gentlemen all belong to."

"But how did you figure this out?" Bischoff asks.

"A few things helped me. There was a lot of depth--many messages to work with. There was consistency--the one-time pads were generated in the same way, always, and always exhibited the same patterns. I made some educated guesses which turned out to be correct. And I had a calculating machine to make the work go faster."

"Educated guesses?"

"I had a hypothesis that the one-time pads were being drawn up by a person who was rolling dice or shuffling a deck of cards to produce the letters. I began to consider psychological factors. An English speaker is accustomed to a certain frequency distribution of letters. He expects to see a great many e's, t's, and a's, and not so many z's and q's and x's. So if such a person were using some supposedly random algorithm to generate the letters, he would be subconsciously irritated every time a z or an x came up, and, conversely, soothed by the appearance of e or t. Over time, this might skew the frequency distribution."

"But Herr Doctor von Hacklheber, I find it unlikely that such a person would substitute their own letters for the ones that came up on the cards, or dice, or whatever."

"It is not very likely. But suppose that the algorithm gave the person some small amount of discretion." Von Hacklheber lights another cigarette, pours out more schnapps. "I set up an experiment. I got twenty volunteers--middle-aged women who wanted to do their part for the Reich. I set them to work drawing up one-time pads using an algorithm where they drew slips out of a box. Then I used my machinery to run statistical calculations on the results. I found that they were not random at all."

Root says, "The one-time pads for Detachment 2702 are being created by Mrs. Tenney, a vicar's wife. She uses a bingo machine, a cage filled with wooden balls with a letter stamped on each ball. She is supposed to close her eyes before reaching into the cage. But suppose she has become sloppy and no longer closes her eyes when she reaches into it."