ADFGVX Cipher
Encode and decode using the ADFGVX cipher. A WWI German field cipher combining substitution and transposition.
6x6 Substitution Grid
| 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 |
How ADFGVX Works
- Replace each character with its ADFGVX coordinates
- Write the result in columns under the transposition key
- Sort columns alphabetically by key letter
- Read off columns to get the ciphertext
History
ADFGVX was used by the German Army during World War I. It was invented by Colonel Fritz Nebel and introduced in March 1918. The letters ADFGVX were chosen because they sound distinct in Morse code, reducing transmission errors.
What is the ADFGVX Cipher?
The ADFGVX cipher was a field cipher used by the German Army during World War I. It combined a modified Polybius square (using 6 letters instead of 5) with columnar transposition, making it one of the most secure field ciphers of its time.
How It Works
Step 1: Fractionation
Each plaintext character is converted to a pair of ADFGVX letters using a 6×6 grid that contains 26 letters and 10 digits.
Step 2: Transposition
The ADFGVX pairs are written in rows under a keyword, then the columns are rearranged alphabetically by the keyword letters and read off.
Why ADFGVX?
These six letters were chosen because they are very distinct in Morse code:
- A: .-
- D: -..
- F: ..-.
- G: --.
- V: ...-
- X: -..-
ADFGVX in Geocaching
This cipher appears in puzzles because:
- WWI theme: Military and history-themed caches
- Two-step process: Makes for interesting puzzle design
- Includes numbers: Can encode coordinates directly
- Historical significance: Famous cryptographic achievement
Cryptanalysis
The ADFGVX cipher was broken by French cryptanalyst Georges Painvin in June 1918, helping the Allies anticipate the German Spring Offensive.
- Short messages: Easier to analyze
- Known plaintext: Standard military phrases helped
- Statistical analysis: After reversing transposition
ADFGX vs ADFGVX
The earlier ADFGX cipher used only 5 letters for a 5×5 grid (25 characters). ADFGVX added the letter V to create a 6×6 grid that could include numbers.