Bazeries Cipher
Invented by a codebreaker — who knew exactly how breakable it was
Why This Matters
Étienne Bazeries broke the Great Cipher of Louis XIV — a code unread for 200 years — and independently reinvented Thomas Jefferson’s wheel cipher. His cylinder design became the basis for the US Army’s M-94, used through World War II.
Étienne Bazeries was one of the most famous cryptanalysts of his era — he broke the Great Cipher of Louis XIV, a code that had protected French royal secrets for 200 years. Ironically, he also designed his own cipher and spent years trying to convince the French military to adopt it, without success.
The Bazeries cylinder — a mechanical device with rotating disks — was independently invented by Thomas Jefferson and later became the basis for the US Army's M-94 cipher device used through WWII.
Step 1: Convert keyword to number (A=1, B=2...)
e.g., 'ATTAQUE' → 1,20,20,1,17,21,5
Step 2: Build Polybius square, columns in
keyword-number order
Step 3: Encrypt using the square
Step 4: Apply transposition using the same
numeric keyword as column order
The Bazeries cipher's two layers are not independent — they share the same keyword. This correlation can be exploited: recovering the transposition key partially constrains the substitution square. Modern hill climbing attacks that search both layers simultaneously can crack it given several hundred characters of ciphertext.
| Concept from Bazeries Cipher | Modern Evolution |
|---|---|
| Single key controls multiple operations | AES key schedule: one master key generates all round keys |
| Inventor = famous codebreaker | Security through obscurity fails: cipher design must be public and peer-reviewed |
| Mechanical cylinder version | Rotor machines: Jefferson Disk → Hebern → Enigma |
| Exhibit | 21 of 37 |
| Era | 1890s · France |
| Security | Broken |
| Inventor | Étienne Bazeries |
| Year | ~1890s |
| Key Type | Numeric keyword (Polybius + transposition) |
| Broken By | Layered frequency analysis |