Cryptonomicon

"Right. Well, what would you like to see?"

"I'm trying to get an overall sense of how the information flows."

"Well, we are close to the beginning of it here--these are the headwaters. Our wellsprings are the Y Service--military and amateur radio operators who listen in on Jerry's radio transmissions, and provide us with these." Packard takes a slip from a motorcyclist's pannier and hands it to Waterhouse.

It is a form with various boxes at the top in which someone has written in a date (today's) and time (a couple of hours ago) and a few other data such as a radio frequency. The body of the form is mostly occupied by a large open space in which the following has been printed in hasty block letters:

A Y W B P R O J H K D H A O B Q T M D L T U S H I

Y P I J S L L E N J O P S K Y V Z P D L E M A O U

T A MO G T M O A H E C

the whole thing preceded by two groups of three letters each:

Y U H A B G

"This one came in from one of our stations in Kent," Packard says. "It is a Chaffinch message."

"So--one of Rommel's?"

"Yes. This intercept came in from Cairo. Chaffinch gets top priority, which is why this message is on the top of the pile."

Packard leads Waterhouse down the central aisle of the hut, between the rows of typists. He picks out one girl who is just finishing up with a message, and hands her the slip. She sets it up next to her machine and commences typing it in.

At first glance, Waterhouse had thought that the machines represented some British concept of how to build an electric typewriter--as big as a dinner table, wrapped up in two hundred pounds of cast-iron, a ten-horse motor turning over under the hood, surrounded by tall fences and armed guards. But now that he is closer he sees that it is something much more complicated. Instead of a platen, it has a large flat reel on it carrying a roll of narrow paper tape. This is not the same kind of tape he saw earlier, smoking through the big machine. This is narrower, and when it emerges from the machine, it does not have holes punched through it for a machine to read. Instead, every time the girl slams down one of the keys on the keyboard--copying the text printed on the slip--a new letter is printed on the tape. But not the same letter that she typed.

It does not take her long to type in all of the letters. Then she tears the tape from her machine. It has a sticky backing which she uses to paste it directly onto the original intercept slip. She hands it to Packard, giving him a demure smile. He responds with something between a nod and a smart little bow, the kind of thing no American male could ever get away with. He glances at it and hands it to Waterhouse.

The letters on the tape say

EINUNDZWANZIGSTPANZERDIVISIONBERICHTET

KEINEBESONDEREEREIGNISSE

"In order to obtain those settings, you have to break the code--which changes every day?"

Packard smiles in agreement. "At midnight. If you stay here--" he checks his watch "--for another four hours, you will see fresh intercepts coming in from the Y Service that will produce utter gibberish when we run them through the Typex, because the Jerries will have changed all their codes on the stroke of midnight. Rather like Cinderella's magic carriage turning back into a pumpkin. We must then analyze the new intercepts using the bombes, and figure out the day's new codes."

"How long does that take?"

"Sometimes we are lucky and have broken the day's codes by two or three o'clock in the morning. Typically it does not happen until after noon or evening. Sometimes we do not succeed at all."

"Okay, this is a stupid question, but I want to be clear. These Typex machines--which merely do a mechanical deciphering operation--are a completely different thing from the bombes, which actually break the codes."

"The bombes, compared to these, are of a completely different, enormously higher order of sophistication," Packard agrees. "They are almost like mechanical thinking machines."

"Where are they located?"

"Hut 11. But they won't be running just now."

"Right," Waterhouse says, "not until after midnight when the carriage turns back into a pumpkin, and you need to break tomorrow's Enigma settings."

"Precisely."

Packard steps over to a small wooden hatch set low into one of the hut's exterior walls. Next to it sits an office tray with a cup hook screwed into each end, and a string tied to each cup hook. One of the strings is piled up loose on the floor. The wall hatch has been slid shut on the other string. Packard puts the message slip on top of a pile of similar ones that has accumulated in the tray, then slides the hatch open, revealing a narrow tunnel leading away from the hut.

"Okay, your pull!" he shouts.

"Okay, my pull!" comes an answering voice a moment later. The string goes taught and the tray slides into the tunnel and disappears.

"On its way to Hut 3," Packard explains.

"Then so am I," Waterhouse says.

***