Enigma Machine
158 quintillion settings. Broken by a crossword puzzle and a weather forecast.
Arthur Scherbius patented the Enigma machine in 1918 as a commercial product. The German military adopted it in 1926 and progressively enhanced it throughout WWII. At its peak, the naval Enigma M4 had 158,962,555,217,826,360,000 possible initial configurations — far beyond any conceivable brute force.
Polish mathematicians Marian Rejewski, Jerzy Różycki, and Henryk Zygalski first broke Enigma in 1932. When Germany added complexity, they passed their work to Britain. Alan Turing and Gordon Welchman at Bletchley Park built the Bombe machine — an electromechanical device that could test configurations far faster than any human. By the end of the war, over 10,000 people worked at Bletchley Park reading German traffic in near-real-time.
Three-rotor Enigma (basic model): 1. Plugboard: swap 10 pairs of letters (150 trillion possible settings) 2. Three rotors: each rotates to next position after each keypress (17,576 rotor position combinations) 3. Reflector: sends signal back through rotors in reverse (this is Enigma's fatal flaw: a letter can never encrypt to itself) 4. Rotor selection: 3 from 5 rotors (60 rotor order combinations) Total: ~158 quintillion settings But: same letter never encrypts to itself → cribs work
Enigma's fatal flaw: a letter can never encrypt to itself (the reflector guarantees this). If you know (or guess) a plaintext word — called a crib — you can eliminate all configurations where any crib letter would encrypt to itself. Weather forecasts always began with WETTER. Messages often ended with HEIL HITLER. These cribs eliminated millions of possible settings. The Bombe machine tested the remaining configurations electromechanically at thousands per minute.
Operators sent lazy key indicators (AAA, BBB), repeated message keys, used predictable cribs (operator's girlfriend's name as daily setting), and sent stereotyped messages. These human failures, not mathematical weaknesses, gave Bletchley Park most of its entry points.
| Concept from Enigma Machine | Modern Evolution |
|---|---|
| Rotor substitution per keypress | AES: key-scheduled S-boxes change per round |
| Reflector = reciprocal (fatal flaw) | Modern ciphers are not reciprocal: encrypt ≠ decrypt in one direction |
| Physical key distribution (codebooks) | Public key cryptography: Diffie-Hellman solved key distribution mathematically |
| Operational errors broke it | Side-channel and operational security remain the weakest links today |
Plaintext: A T T A C K
Settings: Rotors I-II-III, Reflector B
Ring setting: 01-01-01 (AAA)
Plugboard: (A↔M) (T↔G)
Start position: A-A-Z
Encrypting the first letter "A":
1. Plugboard: A → M (A is swapped with M)
2. Rotor III: M → position 12 → maps to J
3. Rotor II: J → position 9 → maps to D
4. Rotor I: D → position 3 → maps to F
5. Reflector B: F → maps to S
6. Rotor I ← S → maps to S
7. Rotor II ← S → maps to E
8. Rotor III← E → maps to P
9. Plugboard: P → P (no swap for P)
Lamp "P" lights up.
Key behaviour: after each keypress,
Rotor III advances one position.
After 26 steps, Rotor II advances.
The wiring path changes every single keypress
— the same letter never encrypts the same way twice.- Lorenz Cipher — Hitler’s strategic teleprinter cipher, broken by Colossus
- One-Time Pad — The only provably unbreakable cipher
- Vigenère Cipher — The polyalphabetic ancestor of rotor machines
| Exhibit | 27 of 37 |
| Era | WWII · 1932–1945 |
| Security | Broken |
| Inventor | Arthur Scherbius (inventor) · German Armed Forces (operator) |
| Year | 1918 (patent) · 1932 (military) |
| Key Type | Rotor wiring + plugboard settings |
| Broken By | Bombe machine · Crib attacks · Alan Turing · Bletchley Park |