ADFGVX Cipher: Substitution Step

ADFGVX is remembered as the German field cipher of 1918, and it keeps showing up in CTFs, museum puzzles and classical cryptography books. If you arrived holding something like DD AV DX DX FF, or you need to produce that shape, this is what the page does: every letter or digit becomes a pair built only from the six letters the cipher is named after.

The matrix is 6x6, filled with A through Z followed by 0 through 9 in plain order, with no keyword scrambling the cells. Each character position becomes a row and a column, and those indexes are labelled A, D, F, G, V and X, chosen precisely because their Morse codes are easy to tell apart and telegraph operators made fewer mistakes. H sits at DD, E at AV, L at DX and O at FF, so HELLO becomes DD AV DX DX FF. Everything that is not a letter or digit is stripped first.

Now the honest part: this is half a cipher. Historical ADFGVX scrambled the matrix with a keyword and then ran a columnar transposition with a second keyword, and that second stage is what scattered the letters and gave analysts a hard time. Without it you are left with plain substitution, which falls to bigram frequency analysis. Use this page to study or to build stage one, never to actually hide anything. It all runs in your browser.