ADFGVX and Fractionation
Study the WWI German ADFGVX cipher that combined substitution with transposition to confound Allied codebreakers.
WWI German Communication Security
By 1918, the German military faced a critical problem: Allied cryptanalysts were breaking their field codes faster than they could be replaced. A new, stronger cipher was urgently needed for the Spring Offensive of 1918.
Colonel Fritz Nebel developed the ADFGVX cipher, which combined two classical techniques in a way that had never been done before in military cryptography.
The ADFGVX Alphabet Choice
The cipher is named after its six ciphertext letters: A, D, F, G, V, X. These letters were chosen deliberately because their Morse code representations are very different from each other.
This minimized transmission errors over field radio. Confusing one letter for another could corrupt an entire message, so the designers selected letters whose Morse patterns are maximally distinguishable.