Why Military Ciphers Matter for Geocaching
Military-themed geocaches often use period-appropriate ciphers. Understanding these historical encryption methods helps you recognize and solve puzzles that reference WWI, WWII, or Cold War themes.
Enigma Machine
Germany • WWII (1930s-1940s)
The Enigma was an electro-mechanical rotor cipher machine used by Nazi Germany. It was considered unbreakable until Polish and British cryptanalysts (including Alan Turing) cracked it at Bletchley Park, shortening WWII by an estimated 2 years.
Recognition Hints
- • Enigma never encrypts a letter as itself
- • The machine was symmetric (encrypt = decrypt with same settings)
- • Daily settings were distributed in codebooks
- • Three-letter message keys were sent twice at the start
Geocaching Tip: Enigma-style puzzles usually simplify the mechanism. Look for references to "rotors" or "plugboard settings" in the cache description.
ADFGX / ADFGVX Cipher
Germany • WWI (1918)
German field cipher using a Polybius square and columnar transposition. Named for the letters used (chosen because they sound distinct in Morse code). Extended to ADFGVX in June 1918 to include digits. Broken by French cryptanalyst Georges Painvin.
How It Works
- 1. Polybius Square: Each letter becomes a pair of ADFGX letters
- 2. Fractionation: Pairs are written in a row
- 3. Columnar Transposition: Columns rearranged using keyword
Example ADFGX grid:
A D F G X A B T A L P D D H O Z K F Q F V S N G G I C U X X M R E W Y
Playfair Cipher
Britain • Crimean War - WWII
Digraph substitution cipher invented by Charles Wheatstone but named after Lord Playfair who promoted it. Used by British in the Boer War and WWI, and by Australian coastwatchers in WWII.
Recognition Hints
- • Encrypts letter pairs (digraphs)
- • Double letters split with X (HELLO → HE LX LO)
- • Ciphertext length is always even
- • I and J typically share a cell in the 5x5 grid
VIC Cipher
Soviet Union • Cold War (1950s)
Complex Soviet spy cipher using straddling checkerboard. Used by spy Reino Häyhänen (codename VIC). One of the most complex pencil-and-paper ciphers, it resisted NSA cryptanalysis for years.
Key Features
- • Uses straddling checkerboard
- • Multiple transposition steps
- • Key derived from song/poem
- • Includes chain addition step
Note: The VIC cipher is rarely used in geocaching due to its complexity, but Cold War-themed caches may reference it. Look for clues about "Soviet codes" or "spy ciphers."
Grille Cipher
Europe • Renaissance - WWI
Transposition cipher using a card with holes (grille). Invented by Gerolamo Cardano in 1550. The grille has holes cut in specific positions. By rotating the grille 90° four times, you can write/read a message.
How It Works
- • Grille is rotated 4 times (0°, 90°, 180°, 270°)
- • Holes must not overlap when rotated
- • Message appears when grille placed on grid
- • Size is typically 4x4, 6x6, or 8x8
Geocaching Tip: Grille ciphers often appear as physical puzzles where you need to create or find a template to overlay on text.
Other Historical Ciphers
Nihilist Cipher
Russia • 19th Century
Used by Russian revolutionaries. Combines Polybius square with keyword addition.
Use Tool →Bifid Cipher
France • 1901
Combines Polybius square with fractionation. Used in early 20th century.
Use Tool →Four-Square Cipher
France • 1902
Uses four 5x5 squares for digraph substitution. Stronger than Playfair.
Use Tool →Historical Timeline
Related Tools
Enigma Machine
WWII rotor cipher
ADFGVX Cipher
WWI German cipher
Playfair Cipher
Digraph substitution
Cardan Grille
Mask-based cipher
Straddling Checkerboard
Cold War spy cipher
Polybius Square
Foundation for many ciphers
Bifid Cipher
Fractionating cipher
Nihilist Cipher
Russian cipher
Columnar Transposition
Used in ADFGX