![]() ![]() However, that was not the only trick that Painvin used to crack the ADFGX cipher. (Considerable statistical analysis was required after that step had been reached, all done by hand.) It was thus effective only during times of very high traffic, but that was also when the most important messages were sent. His method of solution relied on finding messages with stereotyped beginnings, which would fractionate them and then form similar patterns in the positions in the ciphertext that had corresponded to column headings in the transposition table. The work was exceptionally difficult by the standards of classical cryptography, and Painvin became physically ill during it. This cipher might be modified by transposing the rows as well as the columns, creating a harder but improved cipher.ĪDFGVX was cryptanalysed by French Army Lieutenant Georges Painvin, and the cipher was broken in early June 1918. When using the original table containing the secret alphabet, the text can be deciphered. With the keyword, the columns can be reconstructed and placed in the correct order. Then, appending the columns to each other results in this ciphertext: The columns are sorted alphabetically, based on the keyword, and the table changes to this: Usually much longer keys or even phrases were used. ![]() Then, a new table is created with a key as a heading. The text 'attack at 1200am' translates to this: This creates the table below with the letters ADFGVX as column headings and row identifiers: ![]() Digits are inserted after the first occurrences of the letters A (1), B (2) to J (0). This results in the alphabet: NACHTBOMEWRPDFGIJKLQSUVXYZ. In the following example the alphabet is coded with the Dutch codeword ' nachtbommenwerper'. The cipher is based on the 6 letters ADFGVX. That mainly had the effect of considerably shortening messages containing many numbers. That allowed the full alphabet (instead of combining I and J) and the digits from 0 to 9. That expanded the grid to 6 × 6, allowing 36 characters to be used. In June 1918, an additional letter, V, was added to the cipher. Both the transposition keys and the fractionation keys were changed daily. Long messages sent in the ADFGX cipher were broken into sets of messages of different and irregular lengths to make it invulnerable to multiple anagramming. In practice, the transposition keys were about two dozen characters long. Then, it is read off in columns, in keyword order, which yields the ciphertext: Next, the letters are sorted alphabetically in the transposition key (changing CARGO to ACGOR) by rearranging the columns beneath the letters along with the letters themselves: The message is written in rows under a transposition key (here "CARGO"): Next, the fractionated message is subject to a columnar transposition. The first letter of each ciphertext pair is the row, and the second ciphertext letter is the column, of the plaintext letter in the grid ( e.g., "AF" means "row A, column F, in the grid"). I and j have been combined to make the alphabet fit into a 5 × 5 grid.īy using the square, the message is converted to fractionated form: Operation įor the plaintext message, "Attack at once", a secret mixed alphabet is first filled into a 5 × 5 Polybius square: In fact, the Germans believed the ADFGVX cipher was unbreakable. Nebel designed the cipher to provide an army on the move with encryption that was more convenient than trench codes but was still secure. That reduced the possibility of operator error. The letters were chosen deliberately because they are very different from one another in the Morse code. The cipher is named after the six possible letters used in the ciphertext: A, D, F, G, V and X. Invented by the Germans signal corps officers Lieutenant Fritz Nebel (1891–1977) and introduced in March 1918 with the designation "Secret Cipher of the Radio Operators 1918" ( Geheimschrift der Funker 1918, in short GedeFu 18), the cipher was a fractionating transposition cipher which combined a modified Polybius square with a single columnar transposition. ADFGVX was applied from 1 June 1918 on both the Western Front and Eastern Front. ADFGVX was in fact an extension of an earlier cipher called ADFGX which was first used on 1 March 1918 on the German Western Front. It was used to transmit messages secretly using wireless telegraphy. In cryptography, the ADFGVX cipher was a manually applied field cipher used by the Imperial German Army during World War I. ![]()
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