“It works like this. You could create a basic code if the piano or the cello simply gave you the material. Piano plays F-sharp instead of F, cello plays B-flat instead of B—and the listener takes them down as a sequence. But you can create a more complex code this way. Piano plays F-sharp instead of F, cello B-flat instead of B, but not as a sequence. The cello plays far fewer changes, but what it does play is the modifier for all that’s preceded it on the piano.”
“So it is a code?”
“Yep.”
“Do you have any idea what it means?”
“Haven’t a clue, old man. I can tell you how it works in more detail if you like, but I doubt I could crack it. What I can say is this: it doesn’t tell the listener much, but however little it does tell might be vital.
“You may well be able to convey a mathematical formula this way, but language? It’s too brief. This would never translate into syntactical language. There simply isn’t enough data. The most it could be is a mathematical key to something else. The chap who takes down these changes probably has a much larger document. But it’s gobbledygook without this. Until the people who play this give him the code, he might as well try and read Martian.
“You’ve part of the puzzle here, Troy—not the whole jigsaw. It’s like a one-time pad—useless if you don’t know which page you’re supposed to be using—or the settings on the rotors on an Enigma machine—useless without the printed code book, the key that will tell you the positions for each day.”
“The what?” said Troy. “Enigma?”
“The German encoding machine they used throughout the war. We cracked it very early on. But if the Germans switched codebooks, and the Wehrmacht, the Luftwaffe, and the Navy all had different codebooks, we’d be stuffed until we could get hold of one. We’d have no idea of the position or setting of the rotors or of any of the plug-in cables. What I think you have here is the codebook that tells you the settings you need to use to decipher the code on something much larger. I must say, if it is, then it’s an advance because it does away with paper altogether. Once they’ve worked out what they’re playing, the only place it need exist is in the head of the player.”
“Why so complex?”
“Because it’s near-as-dammit foolproof.”