Bazeries Cipher
A historical hand-cipher procedure and an explicitly simplified browser model
Layered frequency analysis
Why This Matters
Étienne Bazeries reconstructed historic French nomenclators and proposed cipher devices of his own. His mechanical cylinder, the hand cipher bearing his name, and this browser’s simplified model are distinct constructions.
Étienne Bazeries was one of the most famous cryptanalysts of his era — he reconstructed a Rossignol-era nomenclator in correspondence from about two centuries earlier. Ironically, he also designed his own cipher and spent years trying to convince the French military to adopt it, without success.
Bazeries proposed a 20-disk cylinder independently of Jefferson’s earlier 36-disk description. The later U.S. M-94 belongs to a related but separately developed cylinder tradition; none of these devices is the two-square hand procedure described below.
ACA hand-cipher convention: choose a number and spell it out to key a 5×5 ciphertext square, merging I/J. The plaintext square has its alphabet written down columns. Reverse groups of plaintext according to successive key digits, then substitute between corresponding square cells.
For example, key 3752 uses successive group lengths 3, 7, 5 and 2. This is group reversal, not columnar transposition.
Browser model boundary: the widget above instead accepts 2–99, builds a 26-letter keyword substitution from the English number name, and reverses fixed-size groups. The size is min(6, max(2, (key mod 7)+2)); key 42 therefore uses pairs. It does not implement the ACA two-square rule or the mechanical cylinder. Its outputs are model exercises, not historical test vectors.
Both layers depend on the key, so their search spaces should not be multiplied as though they were independent. This widget has only 98 selectable numbers, making exhaustive comparison straightforward. That bound applies to this model, not to every historical Bazeries procedure.
| 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 | Compare the separate cylinder tradition with moving wired-rotor machines |
| Exhibit | 22 of 172 |
| Era | 1890s · France |
| Trust | Broken |
| Inventor | Étienne Bazeries |
| Year | ~1890s |
| Key Type | Numeric key; substitution plus group reversal |
| Broken By | Layered frequency analysis |
Sources and Reading
American Cryptogram Association, “Bazeries” specification and worked example; David Kahn, The Codebreakers: The Comprehensive History of Secret Communication from Ancient Times to the Internet, revised edition (1996), Chapter 8, for Bazeries and his separate cylinder. The numerical widget’s rule is documented above so it can be distinguished from the source procedure.