Enigma Rotor Machine — Bench tool
Published 17 Sep 2026 ·
Enigma is the cipher that looks unbeatable on paper and lost a war in practice. Its key space was in the hundred-sextillions and it was broken not by brute force but by noticing that the machine could never encrypt a letter as itself — and that this one fact eliminated almost every wrong key instantly.
- Era
- Modern
- Type
- Polyalphabetic
- Key space
- 158,962,555,217,826,360,000
- Level
- Specialist
IWhat this tool does
Each keypress sends current through three rotors, a reflector, and back through the same three rotors. The right-hand rotor advances one position before every letter. That is what makes the substitution different at every position in the message.
The bench beside this entry reproduces the mechanics: rotors I, II and III, reflector B, ring settings at A, no plugboard. Type a letter and watch a different letter come out; type the same letter twice and get two different outputs, because the rotors have moved in between.
| Component | Choice | Contribution to key space |
|---|---|---|
| rotor order | 3 of 5 rotors arranged | 60 |
| ring settings | 26^3 | 17,576 |
| starting positions | 26^3 | 17,576 |
| plugboard | 10 cables over 26 letters | 150,738,274,937,250 |
Two properties matter more than the arithmetic. First, Enigma is reciprocal: the same settings that encipher also decipher, so no separate decryption mode was needed — and that symmetry is exactly what made it breakable. Second, the reflector guarantees no letter ever maps to itself, which reduces the effective key space enormously for an attacker with a guessed phrase.
IIThe key
The daily key was distributed in a codebook with three parts: rotor order and ring settings for the day, a starting position for each message, and a plugboard wiring that changed every few months.
Multiplying the table above gives roughly 1.59 x 10^23. By any 1930s standard that is beyond mechanical search, and the Germans reasoned accordingly: rotor orders and plugboards were changed under a schedule they believed was unguessable.
The break did not come from reducing the space. It came from finding a property that told the attacker when a guess was wrong.
That property was the no-self-encipherment rule. Guess a fragment of plaintext at a known position — a weather report opening with WETTERVORHERSAGE, a standard salute — and you can check whether any letter would have to encrypt to itself. Almost every wrong placement fails that check instantly, and that is precisely the test Alan Turing's Bombe automated.
IIIWhat it will not protect
Historical ciphers are for study and recreation and are not suitable for protecting real information. The full analysis is in the cipher entry.
Read the full entry, with deciphering steps and weakness analysis →