Cryptonomicon

Now all of a sudden he's reading stuff by guys whose names are preceded by naval ranks and succeeded by M.D.s and Ph.D.s and they are going on for dozens of pages about the physics of nitrogen bubble formation in the knee, for example. There are photographs of cats strapped down in benchtop pressure chambers. Randy learns that the reason Doug Shaftoe doesn't dive to one hundred and fifty-four meters is that certain age-related changes in the joints tend to increase the likelihood of bubble formation during the decompression process. He comes to terms with the fact that the pressure at the depth of the wreck is going to be fifteen or sixteen atmospheres, meaning that as he ascends to the surface, any nitrogen bubbles that happen to be rattling around in his body are going to get fifteen or sixteen times as large as they were to begin with and that this is true whether those bubbles happen to be in his brain, his knee, the little blood vessels of the eyeball, or trapped underneath his fillings. He develops a sophisticated layman's understanding of dive medicine, which amounts to little because everyone's body is different--hence the need for each diver to have a completely different dive plan. Randy will need to figure out his body fat percentage before he can even begin marking up his sheet of graph paper.

It is also path-dependent. These divers' bodies get partly saturated with nitrogen every time they go down, and not all of it goes out of their bodies when they come back up--all of them, sitting around Glory IVplaying cards, drinking beer, talking to their girlfriends on their GSM phones, are all outgassingall the time--nitrogen is seeping out of their bodies into the atmosphere, and each one of them knows more or less how much nitrogen's stuffed into his body at any given moment and understands, in a deep and nearly intuitive way, just exactly how that information propagates through any dive plan that he might be cooking up inside the powerful dive-planning supercomputer that each of these guys apparently carries around in his nitrogen-saturated brain.

One of the divers comes up with a plank from the crate that contained the stacks of gold sheets. It is in very bad shape, and it's still fizzing as gas comes out of it. Fizzing in a way that Randy has no trouble imagining his bones would do if he made any errors in working out his dive plan. There is some stenciled lettering just barely visible on the wood: NIZ-ARCH.

Glory IVhas compressors for pumping air up to insanely high pressures to fill the scuba tanks. Randy develops an awareness that the pressure has to be insanely high or it won't even emerge from the tanks while these guys are down at depth. The divers are all being suffused with this pressurized gas; he half expects that one of these divers is going to bump into something and explode into a pink mushroom cloud.

To: randy@epiphyte.com

From: cantrell@epiphyte.com

Subject: Pontifex

You forwarded me a message about a cryptosystem called Pontifex. Was this invented by a friend of yours? In its general outlines (viz, an n-element permutation that is used to generate a keystream, and that slowly evolves) it is similar to a commercial system called RC4, which enjoys a complicated reputation among Secret Admirers--it seems secure, and has not been broken, but it makes us nervous because it is basically a single-rotor system, albeit a rotor that evolves. Pontifex evolves in a much more complicated & asymmetrical way than RC4 and so mightbe more secure.

Some things about Pontifex are slightly peculiar.

(1) He talks about generating "characters" in the key-stream and then adding them, modulo 26, to the plaintext. This is how people talked 50 years ago when ciphers were worked out using pencil and paper. Today we talk in terms of generating bytes and adding them modulo 256. Is your friend pretty old?

(2) He speaks of T as a 54-element permutation. There is nothing wrong with that--but Pontifex would work just as well with 64 or 73 or 699 elements, so it makes more sense to describe it as an n-element permutation where n could be 54 or any other integer. I can't figure out why he settled on 54. Possibly because it is twice the number of letters in the alphabet--but this makes no particular sense.

Conclusion: the author of Pontifex is cryptologically sophisticated but shows possible signs of being an elderly crank. I need more details in order to deliver a verdict.

–-Cantrell

"Randy?" says Doug Shaftoe, and beckons him into his wardroom.

The inside of the wardroom door is decorated with a big color photograph of a massive stone staircase in a dusty church. They stand in front of it. "Are there a lotof Waterhouses?" Doug asks. "Is it a common name?"

"Uh, well, it's not a rarename."

"Is there anything you'd like to share with me about your family history?"