Chiffriermaschine Enigma I · Walzenlage I–II–III · Umkehrwalze B · sechs Steckerpaare
Enigma — 26 lamps.
159 quintillion wirings.
Three brass drums, a battery, and a lampboard. Every keystroke turns the right-hand drum one twenty-sixth of a revolution before the current flows — so the machine that encrypts your second E is, electrically, a different machine from the one that encrypted your first. Watch the amber path below: keyboard, plugboard, three rotors, reflector, and back. It never draws the same road twice. Type on your own keyboard — the machine is yours.
The odometer that counts wrong on purpose
Press the same key twice. The lamp differs.
A fixed substitution cipher dies of statistics — count the letters and E gives itself away. Enigma's answer: move the cipher every stroke. The right drum steps like an odometer digit; at its turnover notch it carries the middle drum, and the middle carries the left. One press, one new alphabet.
The carry has a famous defect. When the middle drum sits on its own notch it drags itself over along with its neighbour — watch the window read ADV → AEW → BFX in the machine's first strokes. This double-step makes the middle drum move twice in a row and trims the full cage cycle from 26³ = 17,576 positions to 16,900 — a genuine mechanical anomaly of the stepping pawls, faithfully reproduced here.
The lock, counted
One machine, counted out
158,962,555,217,826,360,000
- Rotor orders — three drums chosen from five60
- Ground positions — 26 × 26 × 2617,576
- Plugboard pairings — ten cords across 26 sockets150,738,274,937,250
Roughly 1.6 × 10²⁰ daily keys — the commonly cited figure for the ten-plug service Enigma. Count ring settings too, or fewer cords, and sources land elsewhere; every version of the number is astronomical. The German cryptographers concluded that trying keys was hopeless. They were right. Bletchley Park never searched the keyspace — it walked around it.
This exhibit runs one point in that space: rotors I–II–III, reflector B, ring settings A-A-A, six plug pairs, ground setting ADS. Its wirings are the historically documented tables, reproduced in the plate below.
The honest failure
The lamp that never lights
The reflector is the machine's elegance: it folds the current back so that encryption and decryption are the same act — set the same key, type the ciphertext, read the message. But a folded circuit can never return down the wire it entered. No letter, ever, encrypts to itself. Press E for a lifetime; the E lamp stays dark.
That single certainty was Bletchley Park's lever. Slide a guessed phrase — a crib like WETTERVORHERSAGE, the morning weather report — along an intercept, and every alignment where any letter faces itself is impossible, discarded for free. The survivors were few enough for the bombes to test. The counter above is live: it has never left zero, and that is precisely what broke the machine.
Machine plate
Honest to the wiring tables
| Walze I | EKMFLGDQVZNTOWYHXUSPAIBRCJ · turnover Q |
|---|---|
| Walze II | AJDKSIRUXBLHWTMCQGZNPYFVOE · turnover E |
| Walze III | BDFHJLCPRTXVZNYEIWGAKMUSQO · turnover V |
| Umkehrwalze B | YRUHQSLDPXNGOKMIEBFZCWVJAT |
| Steckerbrett | AM FI NV PS TU WZ — six pairs, in the style of the earliest daily key sheets |
| Stepping | Right drum every stroke; middle at right's notch; middle and left when the middle sits on its own notch (double-step). Rotors move before the circuit closes. |
Check it yourself: with rotors I–II–III at AAA and no plug cords, typing AAAAA lights B D Z G O — the standard test vector for these tables. This page's machine passes it.