Cryptonomicon

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: randy@epiphyte.com

From: root@eruditorum.org

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.