ADFGX cipher decoder and encoder

The ADFGX cipher was used by the German Army during World War I. It was invented by Lieutenant Fritz Nebel and is a fractionating transposition cipher which combines a Polybius square with a columnar transposition. The name comes from the five possible letters used: A, D, F, G and X. These particular letters were chosen because they are very different from each other in Morse code, which reduced the risk of telegraphy operator errors. Later, the letter V was added to the ADFGX cipher so it could represent more characters and became known as the ADFGVX cipher.

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ADFGX cipher tool

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Polybius square


                    

Transposition grid


                

Features

  • The ADFGX cipher is a combination of a Polybius square and a columnar transposition cipher.
  • It is simple enough to be possible to carry out by hand.
  • It can encrypt 25 characters. Because the alphabet has 26 letters, one letter has to be replaced by another (for example replacing j by i).
  • During World War I, the Germans believed the cipher was unbreakable. It was however broken by a French cryptanalyst in 1918. As a direct result, the French army discovered where the Germans were planning to attack.

Sample text

DXXADDDDADDAADFFAGGFXDXXFFAXGGAXFDADGDFFGXAAFF

The ciphertext above represents "LET THE GREAT PLOT COMMENCE" encrypted using the keys POLYBIUS and SQUARE.