Cryptonomicon

shelves of Glory IVand tries to come up with even a vague idea of what Doug's talking about. Randy has never gone scuba diving in his life, but he's seen them doing it on Jacques Cousteau and it seems straightforward enough.

The first three books he consults contain more than enough detail to perfectly reproduce the crestfallenness that Randy experienced when he learned about flightplans. Before he'd opened the books Randy had gotten out his mechanical pencil and his graph paper in preparation for making marks on the page; half an hour later he's still trying to get a handle on the contents of the tables, and he hasn't made any marks at all. He notes that the depths in these tables only go down as far as a hundred and thirty, and at that level they only talk in terms of staying down there five or ten minutes. And yet he knows that Amy, and the Shaftoe's colorful and ever-enlarging cast of polyethnic scuba divers, are spending much longer at this depth, and are in fact beginning to come up to the surface with artifacts from the wreck. There is, for example, an aluminum briefcase wherein Doug hopes to find clues as to who was on this U-boat and why it was on the wrong side of the planet.

Randy begins to fear that the entire wreck is going to be stripped bare before he even makes any marks on his piece of graph paper. The divers show up, one or two each day, on speedboats or outrigger canoes from Palawan. Blond surf boys, taciturn galoots, cigarette-smoking Frenchmen, Nintendo-playing Asians, beer-can- crumpling ex-Navy guys, blue-collar hillbillies. Theyall have diving plans. Why doesn't Randy have a diving plan?

He starts sketching one out based on the depth of one hundred and thirty, which seems reasonably close to one hundred and fifty-four. After working on it for about an hour (long enough to imagine all sorts of specious details) he happens to notice that the table he's been using is in feet,not meters,which means that all of these divers have been going down to a depth that is way more than three times as deep as the maximum that is even talked about on these tables.

Randy closes up all of the books and looks at them peevishly for a while. They are all nice new books with color photographs on the covers. He picked them off the shelf because (getting introspective here) he is a computer guy, and in the computer world any book printed more than two months ago is a campy nostalgia item. Investigating a little more, he finds that all three of these shiny new books have been personally autographed by the authors, with long personal inscriptions: two addressed to Doug, and one to Amy. The one to Amy has obviously been written by a man who is desperately in love with her. Reading it is like moisturizing with Tabasco.

He concludes that these are all consumer-grade diving books written for rum-drenched tourists, and furthermore that the publishers probably had teams of lawyers go over them one word at a time to make sure there would not be liability trouble. That the contents of these books, therefore, probably represent about one percent of everything that the authors actually know about diving, but that the lawyers have made sure that the authors don't even mentionthat.

Okay, so divers have mastered a large body of occult knowledge. That explains their general resemblance to hackers, albeit physically fit hackers.

Doug Shaftoe is not going down to the wreck himself. As a matter of fact he looked surprised, bordering on contemptuous, when Randy asked him whether he wouldgo down. Instead, he's going over the stuff that is brought up from the wreck by the younger divers. They began by doing a photographic survey, using digital cameras, and Doug's been printing out blowups of the inside of the U-boat on his laser printer and pasting them up around the walls of his personal wardroom on Glory IV.

Randy does a sorting procedure on the diving books now: he ignores anything that has color photographs, or that appears to have been published within the last twenty years, or that has any quotes on the back cover containing the words stunning, superb, user-friendly,or, worst of all, easy- to-understand.He looks for old, thick books with worn-out bindings and block-lettered titles like DIVE MANUAL. Anything with angry marginal notes written by Doug Shaftoe gets extra points.

To: [email protected]

From: [email protected]

Subject: Pontifex

Randy,

For now, let's use 'Pontifex' as the working title of this cryptosystem. It is a post-war system. What I mean by that is that, after seeing what Turing and company did to Enigma, I came to the (now obvious) conclusion that any modern system had better be resistant to machine cryptanalysis. Pontifex uses a 54-element permutation as its key-one key per message, mind you!-and it uses that permutation (which we will denote as T) to generate a keystream which is added, modulo 26, to the plaintext (P), as in a one-time pad. The process of generating each character in the keystream alters T in a reversible but more or less 'random' fashion.

At this point, a diver comes up with a piece of actual gold, but it's not a bar: it's a sheet of hammered gold, maybe eight inches on a side and about a quarter of a millimeter thick, with a pattern of tiny neat holes punched through it, like a computer card. Randy spends a couple of days obsessing over this artifact. He learns that it came out of a crate stored in the hold of the U-boat, and that there are thousands more of them.

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: [email protected]

From: [email protected]

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.