Definition
The ADFGVX cipher is a file cipher that the Germans used in World War I. Colonel Fritz Nebel developed it in 1918, and it was one of the most complex encryption methods at the time. Nonetheless, Georges Painvin broke the cipher and was abandoned after that.
How the ADFGVX Cipher Works
- Create a six-by-six key square with letters A, D, F, G, V, and X as the column and row headers while the remaining letters (excluding duplicates) take the other cells.
- Split the plaintext message into single letters or pairs, then encrypt them with the ADFGVX fractionation method. In fractionation, you locate the letter or pair in the key square and replace it with the corresponding row and column header letters.
- Use a single substitution cipher to re-encrypt the results with a predetermined substitution keyword that organizes the alphabet for encoding.
- Shift (transpose) the final result with a pre-agreed transposition key to improve security.
- Reverse the process to decrypt the ciphertext using the key square, the replacement keyword, and the transposition key to reveal the original plaintext.