ADFGVX cipher definition
The ADFGVX cipher is a field cipher that was developed in 1918 and used by the German army during World War I. At the time of its creation, it was one of the most complex ciphers ever developed. Regardless of this fact, the cipher was broken by Georges Painvin soon after its introduction and abandoned after the war.
The cipher’s name comes from the six letters it uses for encryption: A, D, F, G, V, and X. The ADFGVX cipher is a combination of a fractionating and a transposition cipher. It involves a series of steps, including fractionation, substitution, and transposition, to convert plaintext into ciphertext.
How the ADFGVX cipher works
- Create a key square — a six-by-six matrix with the letters A, D, F, G, V, and X as the row and column headers and the remaining letters (excluding duplicates) in the other cells.
- Break down the plaintext message into individual letters or pairs, then encrypt those letters or pairs using the ADFGVX fractionation process. In fractionation, you find the letter or pair in your key square and substitute it with the letters in the row and column headers.
- Encrypt the result again using a single-letter substitution cipher, with an agreed-upon substitution keyword determining the order of the letters in the alphabet for substitution.
- Transpose (shift) the final result for added security using an agreed-upon transposition key.
- To decrypt the ciphertext, follow this process in reverse, using the key square, the substitution keyword, and the transposition key to get the original plaintext.