Cryptography Reference
In-Depth Information
Exploiting the circumstance that the Enigma doesn't transform any char-
acter onto itself, and considering the poorly selected keys, and knowing
the rotor wiring, they were able to recover the message key.
The Warsaw-based factory AVA began building a device that tabulated
conformities of the Enigma. Again, Rejewski was one of the major play-
ers. Using the tables, they were able to find the day keys within 10 to 20
minutes. That was back in 1937.
Putting the same string twice at the beginning was the ciphering error.
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The ring setting, i.e., the positions of the rings on the rotors, could be
revealed by mounting a plaintext attack. That was the point where another
ciphering error by the radio operators materialized: most of the texts
began with ANX, where 'X' stood for a blank (and 'AN' means 'TO').
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In 1938, the Wehrmacht changed the message-key method. The for-
mer methods became ineffective, but the leading double message key
remained in effect. The Polish cryptanalysts used self-developed machines
as their only means to search for plaintext patterns in the form 123123.
These machines looked somewhat like iced cakes, called 'bomba' in
Polish. This was the reason why their expanded successors carried the
misleading name 'bomb' in Great Britain later on. Such a 'bomba' found
the key within two hours.
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A little later, still in 1938, the Wehrmacht approved two additional rotors
to be used in the Enigma. At this point, the reconnaissance planes owed
something important to chance: the military intelligence encrypted each
radiogram initially by means of a digram method before they passed it on
to the operators for encoding on the Enigma. In Poland, they first thought
it to be a method different from the Enigma. Inadvertently, however, the
number '1' sneaked into a digram ciphertext. The operator diligently
typed it into the machine as a ONE. Poland noticed and understood that
this had to be a multiple encryption. It took little effort to break the
digram method.
When they introduced the two new drums, the military intelligence didn't
change their digram method, which meant that the drums could be ana-
lyzed as before. Their structure quickly became known. Again, the attack-
ers knew the adversary's full algorithm.
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In 1939, just before the war broke out, the findings won in Poland trav-
eled to Great Britain. There, the famous mathematician Turing busied
himself with the Polish 'bombas' and improved them. (Turing is famous
