Tool to decrypt/encrypt with ADFGVX. ADFGVX is a German encryption system unsing a 6x6 square grid and letters A,D,F,G,V,X and then this ciphertext get a permutation of its letters (transposition).
ADFGVX Cipher - dCode
Tag(s) : Substitution Cipher, Transposition Cipher
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The encryption uses a 6x6 square grid of 36 distinct characters (usually the latin alphabet and the 10 digits from 0 to 9). Lines and columns named, from top to bottom and from left to right, by the letters A, D, F, G, V and X. Each character of the plain text must exist in the grid in order to be localized by a coordinate (line, column).
Example: A grid filled with AZERTYUIOPQSDFGHJKLMWXCVBN0123456789: such as A = (A,A), B = (V,A), C = (G,V), D = (F,A) etc.
By replacing each letter of the message with the pair of coordinates, the intermediate ciphered message is then a substitution with bigrams.
Example: DCODE becomes FA,GV,DF,FA,AF
This message will get another encryption by columnar transposition. The transposition uses a permutation key/keyphrase, usually based on a keyword. This can be found it by rearranging its letters in alphabetic order. Two same letters are ranked in order of appearance, but if possible avoid duplicates letters in the keyphrase as this can lead to encryption/decryption errors.
Example: KEY => K(1),E(2),Y(3) => E(2),K(1),Y(3) => 2,1,3
The message is written in a table whose width is the key size. Empty box are filled with X (or another letter).
Columns are rearranged such as the permutation key.
Example: Column 1 (K) switches with column 2 (E)
The final ciphertext is created by reading the letters of the table by columns starting from top to bottom and from left to right.
Example: Final encrypted message is ADAXFVFFGFAX (message often transmitted in Morse code)
The ADFGVX decryption process requires a key and a grid.
Example: The cipher text is AD,AX,FV,FF,GF,AX and the keyword is KEY (that correspond to permutation K(1),E(2),Y(3) => E(2),K(1),Y(3) => 2,1,3)
The ciphered message is then written from top to bottom and from left to right in a table with $ n $ columns where $ n $ is the length of the key. Columns are named according to the letters of the key, rearranged in alphabetic order.
Reading the table by row gives the intermediate message.
For each bigrams, replace it with the corresponding letter with coordinates (line, column) in the grid to get the plain text message.
Example: FA = line F, column A = D then GV = C, etc. The original plain text is DCODE.
The ciphertext must contain only 6 distinct characters: A, D, F, G, V and X.
Theorically, the ciphered message should have number of character that is divisible by the permutation key length.
The letters A, D, F, G, V and X have been selected because their equivalent in morse code are very distinguishable, his prevent transmission error by radio
ADFGVX cipher have been introduced at the end of the First World War (from 1917) by Fritz Nebel. He have been used on the 5th of March 1918 during the german attack of Paris, it was using an ADFGX version (with the letters A, D, F, G and X only).
GEDEFU 18 for GEheimschrift DEr FUnker 18, which can be translated in radio-operators' cipher 18 is the old name of ADFGVX cipher.
The crack is attributed to Georges-Jean Painvin. Among the deciphered messages, one text was nicknamed The radiogram of the victory because it allowed France to win a battle in June 1918.
George-Jean Painvin deciphered a first message in June 1918.
The theorem of Roitelet is a novel by Frédéric Cathala here (link) which has as protagonist a spy during the first world war having messages encrypted with ADFGVX.