THE LAST GOOD WAR: A Novel Read Online Free PDF Page B

the third wheel is a reflector. It means that the machine also works the other way round: if you pressed T, you would get A. Thus, the same machine is used either for coding or decoding.”
    "Great. So we've been developing it for the Polish Air Force?"
    "Not exactly. It's a copy of a German machine."
    Anna wondered where they had gotten it but didn't want to seem too curious.
    Henryk read her mind. "It was invented in 1919 and manufactured by a German company, who sold it commercially to railroads and other businesses who wanted to keep their communications secret. We bought one, but the Germans stopped selling them when the machine was adopted by their army in 1926. Our technical services are in the process of making additional copies."
    Henryk didn't want to give the least hint that they had a spy in Germany. Accordingly, he hadn't told the whole truth—that the Germans were using a modified version, with different rotors, and that Marian had worked out the wiring of the new ones, using information supplied by Schmidt.
    "I suppose our task is to decipher the German messages by figuring out the setting of the wheels."
    "Right you are."
    "Let's see. The right-hand wheel can be set with any letter at the top? That's 26 positions. The same is true of the other two?” Henryk nodded. "That's 26 x 26 x 26 possible settings... over 15 thousand."
    "17,576, to be exact. If you pushed the keys 17,576 times, your setting would come back to where it started.”
    “Like an odometer on a car? Once it reaches 99999, it turns back to 00000—provided the car hasn't fallen apart by that time.”
    "Exactly.... Or maybe not exactly,” added Henryk. “A new car starts at 00000. But with the Enigma, the Germans don't start at AAA. They can start anywhere. And, as far as we can tell, they use a different setting for every message.”
    "So what's left is brute force—trying each setting for every message?” Anna wondered.
    "Yes and no. That's one place to begin. But our game will be to figure out some pattern—so we don't have to run through all 17,000."
    "We've got a good place to start," said Jerzy, “a long, clear intercepted message.” He slid several papers across to Anna. She was distracted by the cloud of cigar smoke when he leaned across the table, but tried to ignore it as she looked down at the papers. She could read the first few lines, but they were followed by a jumble of letters:
    Discriminant: Blue
    Seventy-two
    One hundred and twenty eight
    Then came a line with six apparently random letters, in two groups of three:
    DSI FDR
    The next line was a series of 50 or 60 letters.
    Next came groups of five letters each, filling a number of lines.
    “First,” explained Marian, “is the so-called discriminant—Blue. It appears in about 40 percent of the messages. It indicates the army; anyone with a blue codebook will be able to look up the initial settings of the rotors for army messages. There are different settings for different organizations—red, green, orange, and so on—so they can't read one another's mail.
    “The next line, 72, is the number of letters giving the address—from so and so to such and such—and the date. Then comes 128, the number of letters in the main message. They're divided into groups of five to help the recipient keep track; if he only has four letters in a group, he knows he's dropped one letter and he knows where. If he doesn't keep track, the wheels won't click the right number of times, and he won't get anything but gibberish.
    "Our best guess is that the six letters—two groups of three each—have something to do with the resetting of the rotors. We're not sure; the Germans have changed their procedures since we were able to break some messages several years ago. What we do know is that, once we figure out the wheel settings for the address, the settings don't change again, at least not for that particular message; we can read through the rest of it.”
    There was a knock on the door.