ADFGVX cipher

ADFGVX is the enhanced version of ADFGX, entering German military use in June 1918. The only difference from its predecessor: a sixth label, V, which lets the grid grow from 5×5 (25 cells) to 6×6 (36 cells).

This enlargement solves a real problem: ADFGX couldn’t cipher digits (0-9) directly — they had to be spelled out (eins, zwei, drei), lengthening messages and aiding analysis. ADFGVX embeds all ten digits in the grid next to the 26 letters.

How does ADFGVX cipher work?

Step 1 — 6×6 Polybius

The grid holds 36 cells (26 letters + 10 digits), shuffled by a secret key:

    A D F G V X
  A A B C D E F
  D G H I J K L
  F M N O P Q R
  G S T U V W X
  V Y Z 0 1 2 3
  X 4 5 6 7 8 9

Each plain character is replaced by the pair (row-label, col-label). For instance: C → AF, I → DF, E → AV, 7 → XV.

Step 2 — Columnar transposition

Identical to ADFGX: the intermediate text (ADFGVX pairs) is written into a rectangular grid under a keyword, then read column by column in the alphabetic order of the keyword letters.

Example (step 1 only)

Plaintext CIPHE with the grid above:

C → A F    I → D F    P → F G    H → D D    E → A V

Result: AFDFFGDDAV.

What is the history of ADFGVX cipher?

• March 1918: ADFGX enters service.
• June 1918: ADFGVX replaces ADFGX so digits can be transmitted directly.
• May–June 1918: Georges Painvin breaks the method (both variants) by exploiting formatted military headers and multiple same-length messages. The French army then reads parts of the German traffic during the 1918 offensives — a decisive edge.

Painvin worked sleeplessly for weeks to break the system; he emerged exhausted and fell seriously ill. His work is regarded as one of the founding acts of modern cryptanalysis.

Variants and descendants

• ADFGX — 5-label predecessor, no digits.
• Schlüsselzusatz 42 (SZ 42, Lorenz) — German strategic-level machine used in WWII, far more complex.
• JN-25 — WWII Japanese naval code, similar principle (super-enciphered codebook).

What are the weaknesses of ADFGVX cipher?

Same as ADFGX, with the extra difficulty offered by the enlarged alphabet:

• Formatted messages with fixed headers → exploitable cribs.
• Multiple same-length messages → geometric constraints on the transposition.
• Statistics on symbol pairs once the transposition is undone.

In CipherChronicle

ADFGVX is the peak of WWI hand ciphers: a carefully layered double step, breakable only with intense human work and multiple ciphertexts. Its grids can stage the two-phase resolution and the historical dimension.