ADFGVX cipher decoder
Decrypt ADFGX and ADFGVX - a Polybius substitution followed by a columnar transposition, and unmistakable from its six-letter alphabet.
Open in ctfpalADFGVX is instantly recognisable: the ciphertext contains only the letters A, D, F, G, V, and X. Those six were chosen because they are maximally distinct in Morse code, so garbled radio transmissions were still decodable.
Two stages, two keys
First a 6x6 Polybius square maps each plaintext character (26 letters plus 10 digits) to a pair of the six letters. Then a keyed columnar transposition scrambles the resulting stream. The combination is what made it strong for its time: the fractionation splits each character across two positions, and the transposition then separates those positions from each other.
To decrypt you need both the transposition keyword and the square. Undo the transposition first, then read the result off in pairs through the square. ADFGX is the earlier five-letter variant with a 5x5 square and no digits.