Enigma Read Online Free PDF

looked worth the cost of two men’s
lives: two little pamphlets, the Short Signal Book and the Short
Weather Cipher, printed in soluble ink on pink blotting paper,
designed to be dropped into water by the wireless operator at the
first sign of trouble. But to Bletchley they were beyond price,
worth more than all the sunken treasure ever raised in history.
Jericho knew them by heart even now. He closed his eyes and the
symbols were still there, burned into the back of his retina.
    T = Lufttemperatur in ganzen Celsius-Graden.—28C = a.—27C =
b.—26C…
    U-boats made daily weather reports: air temperature, barometric
pressure, wind-speed, cloud-cover…
    The Short Weather Cipher book reduced that data to a half-dozen
letters. Those half-dozen letters were enciphered on the Enigma.
The message was then broadcast from the submarine in Morse code and
picked up by the German Navy’s coastal weather stations. The
weather stations used the U-boats’ data to compile meteorological
reports of their own. These reports were then re-broadcast, an hour
or two later, in a standard three-rotor Enigma weather cipher—a
cipher Bletchley could break—for the use of every German
vessel.
    It was the back door into Shark.
    First, you read the weather report. Then you put the weather
report back into the short weather cipher. And what you were left
with, by a process of logical deduction, was the text that had been
fed into the four-rotor Enigma a few hours earlier. It was a
perfect crib. A cryptanalyst’s dream.
    But still they couldn’t break it.
    Every day the code-breakers, Jericho among them, fed their
possible solutions into the bombes—immense electro-mechanical
computers, each the size of a walk-in wardrobe, which made a noise
like a knitting machine—and waited to be told which guess was
correct. And every day they received no answer. The task was simply
too great. Even a message enciphered on a three-rotor enigma might
take twenty-four hours to decode, as the bombes clattered their way
through the billions of permutations. A four-rotor Enigma,
multiplying the numbers by a factor of twenty-six, would
theoretically take the best part of a month.
    For three weeks Jericho worked round the clock, and when he did
grab an hour or two’s sleep it was only to dream fitfully of
drowning men. “Let’s just hope they were dead before they hit the
bottom…” His brain was beyond tiredness. It ached physically, like
an overworked muscle. He began to suffer blackouts. These only
lasted a matter of seconds but they were frightening enough. One
moment he might be working in the Hut, bent over his slide-rule,
and the next everything around him had blurred and jumped on, as if
a film had slipped its sprockets in a projector. He managed to beg
some Benzedrine off the camp doctor but that only made his mood
swings worse, his frenzied highs followed by increasingly
protracted lows.
    Curiously enough, the solution, when it came, had nothing to do
with mathematics, and afterwards he was to reproach himself
furiously for becoming too immersed in detail. If he had not been
so tired, he might have stepped back and seen it earlier.
    It was a Saturday night, the second Saturday in December. At
about nine o’clock Logie had sent him home. Jericho had tried to
argue, but Logie had said: “No, you’re going to kill yourself if
you go on at this rate, and that won’t be any use to anyone, old
love, especially you.” So Jericho had cycled wearily back to his
digs above the pub in Shenley Church End and had crawled beneath
the bedclothes. He heard last orders called downstairs, listened as
the final few regulars departed and the bar was closed up. In the
dead hours after midnight he lay looking at the ceiling wondering
if he would ever sleep again, his mind churning like a piece of
machinery he couldn’t switch off.
    It had been obvious from the moment Shark had first surfaced
that the only acceptable, long-term solution was to redesign the
bombes to