Breaking the Mystory Enigma

PLAIN_TEXT: OBERKOMMANDODERWEHRMACHT CIPHERTEXT: ZMGERFEWMLKMTAWXTSWVUINZ

The German Army Military Enigma Encryption Machine had four 26-contact rotors. The fourth rotor, or Umkerwalze, was a half rotor. This reflecting rotor caused current entering it to be turned back through the three previous rotors along a different path from that taken upon entry. The reflecting principle meant that, at any rotor setting, if a given letter, let us say A enciphered into W, then W must also encipher into A. One had only to arrange the rotors in the same order and starting position as used in encipherment and then type the ciphertext letters to recover the plain text. Because of the routine stereotyping found in many current German texts, it seemed feasible to base a new method upon the use of probable plain text. British mathematician Alan Turing pondered the problem. Turing's idea was for a high speed machine which would step through all possible rotor positions while testing each position for probable plain text beginning at that location. Be your own Alan Turing.