Enigma Machine Simulator: Encrypt, Decode & Trace the Signal Path

A historically accurate Enigma machine — rotors, reflectors, ring settings, plugboard, and live signal-path visualization.

This is a historically accurate rebuild of the Enigma I / M3 machine used by the German military before and during the Second World War — real rotor wirings, real reflector wirings, ring settings, a plugboard, and the mechanical double-stepping quirk that real Enigma operators had to live with, reproduced down to a character-by-character trace of the electrical signal path. It is a working replica of a code that was broken more than eighty years ago, not a suggestion for keeping anything secret today.

How to decrypt an Enigma message

Open Machine settings and set the sender's rotor order from left to right, each rotor's ring setting and the reflector. The defaults are rotors I, II and III with reflector UKW-B and every ring at 01 (A).
Type the plugboard pairs into the Steckerbrett field, separated by spaces or commas, for example AB CD EF. Up to 10 pairs are allowed, and each letter can appear in only one pair.
Set each rotor's start position to the letters the message began at. Changing any setting resets the machine and clears the typed text, so set everything before you type.
Click the typing box and type or paste the ciphertext. Each letter goes through the machine in turn, spaces, digits and punctuation are dropped, and the plaintext builds up in the lampboard output.
Press Reset & decode ciphertext with same settings to replay the lampboard output from the start position and confirm the round trip. Gibberish means at least one setting differs from the sender's.

The parts, all modeled individually

Five historical rotors (I through V) are available, each with its own documented internal wiring and its own single turnover notch letter — the mnemonic 'Royal Flags Wave Kings Above' gives the notch letters Q, E, V, J and Z for rotors I through V in order, and this simulator uses exactly those. Three historical reflectors (A, B and C) are included, each a self-reciprocal wiring where every letter pairs with a distinct partner and never maps to itself, matching how a real reflector's wiring loops back the signal.

Ring settings (Ringstellung) shift each rotor's internal wiring relative to its outer letter ring, and the plugboard (Steckerbrett) swaps up to ten letter pairs before the signal ever reaches the rotors — both configurable exactly as they were on the real machine. Stepping follows the real mechanical rule set, including the documented double-stepping anomaly, where the middle rotor advances twice in a row under a specific notch-alignment condition rather than the simple 'one rotor steps per keystroke, carrying over at a notch' rule a simplified simulator might use instead.

Enigma settings glossary

German key sheets listed the day's settings under these names, and the simulator labels its controls with the same terms.

Walzenlage (rotor order): which of rotors I–V sit in the left, middle and right slots. The right rotor steps on every key press and the left one steps least often.
Ringstellung (ring setting): turns a rotor's internal wiring against its lettered ring, numbered 01–26 (A–Z). The turnover notch is fixed to the ring, so the rotor still turns its neighbour at the same window letter.
Grundstellung (start position): the three letters showing in the rotor windows before the first key is pressed.
Umkehrwalze (reflector, UKW): the fixed wheel at the far end that sends the signal back through the rotors. Here you can fit UKW-A, UKW-B or UKW-C.
Steckerbrett (plugboard): cables that swap pairs of letters on the way into and out of the rotors. Wartime procedure typically used 10 cables, the maximum this simulator accepts.

Which Enigma models this simulates

The wiring tables cover the three-rotor Enigma I used by the German army and air force and the naval M3, which share rotors I to V; between them they used reflectors A, B and C, all three of which are included. Rotors VI, VII and VIII, which were naval-only and carried two turnover notches each, are not modelled.

The four-rotor M4 is not supported either. It needs the thin Beta or Gamma wheel and the thin B or C reflector, so U-boat traffic enciphered on an M4 cannot be reproduced here, and commercial, railway and Abwehr machines with their own wirings are also outside this model. One liberty the simulator takes: it lets you place the same rotor in two slots, which a real set with one wheel of each type could not do.

Verified against the historical record, not just self-consistent

Every rotor wiring, reflector wiring and notch letter in this simulator was cross-checked against Wikipedia's Enigma rotor details reference and corroborated against cryptomuseum.com, both of which list the same 26-letter wiring strings for each component. Beyond internal consistency, the simulator's output is checked against a documented worked example: rotors I, II and III in that order, wide reflector B, all ring settings at A, typing AAAAA from the AAA starting position produces BDZGO — and the same setup with every ring setting moved to B instead produces EWTYX. Both of those known answers are captured as tests independent of this simulator's own round-trip symmetry check, so an internal bug that happened to still encrypt-then-decrypt back to the original text wouldn't be enough to pass.

How many settings did Enigma have?

The usual figure counts the choices an army operator made with a box of five rotors and ten plugboard cables. Multiply the three independent parts listed below and you get 158,962,555,217,826,360,000, about 1.59 × 10²⁰.

That figure leaves out ring settings, because changing a ring largely does the same job as changing a start position. Counting the middle and right rings, which shift when turnovers happen, would multiply it by up to 676 (26 × 26), to roughly 1.07 × 10²³. The number was never what protected Enigma, though: the bombes at Bletchley Park did not try every setting, they used guessed plaintext and the rule that no letter encrypts to itself to discard almost all of them.

Rotor order: 5 × 4 × 3 = 60 ways to put three of the five rotors into three slots.
Start positions: 26 × 26 × 26 = 17,576 window combinations.
Plugboard with 10 cables: 26! ÷ (6! × 10! × 2¹⁰) = 150,738,274,937,250 ways to pair up 20 letters and leave 6 unplugged.
Total: 60 × 17,576 × 150,738,274,937,250 = 158,962,555,217,826,360,000.

Watching the signal path, not just the output letter

Every character you type produces a visible trace of the full path a signal actually takes through a real machine: through the plugboard, through each rotor in turn (accounting for its current position and ring setting), off the reflector, back through the same rotors in reverse, and back through the plugboard once more to the letter that lights up. That step-by-step view is what makes the machine's core weakness visible rather than abstract: no letter can ever encrypt to itself, a direct consequence of the reflector's self-reciprocal wiring, which turned out to be one of the cracks Allied cryptanalysts used to break real Enigma traffic.

A broken code, kept for what it teaches

Enigma's fatal weaknesses — a letter can never encrypt to itself, the plugboard and rotor settings still leave exploitable structure, and operator habits like reusing message keys gave analysts a foothold — were found and exploited by Polish and then British cryptanalysts at Bletchley Park using both mathematical analysis and purpose-built electromechanical machines, well before modern computing existed.
This simulator exists to teach how a historically important cipher machine actually worked, mechanically and electrically, not as a cryptographic tool for protecting anything you care about keeping secret.
If you need real confidentiality today, use a modern authenticated cipher such as AES-GCM or ChaCha20-Poly1305 — this catalog's symmetric-cipher tool runs real AES through the browser's own cryptographic engine, and it's the appropriate tool for that job, not this one.

Questions people ask about Enigma Machine Simulator

Is this Enigma simulator historically accurate, or a simplified version?: The rotor wirings, reflector wirings, notch letters and stepping mechanics — including the double-stepping anomaly — are all modeled on the real Enigma I / M3 machine and were cross-checked against two independent historical references. The simulator's output also matches a documented worked example letter for letter, which is a stronger check than only confirming it decrypts its own ciphertext correctly.
Why can a letter never encrypt to itself on this simulator?: Because the reflector's wiring is self-reciprocal — every letter pairs with a different letter and the signal always bounces back through a partner, never straight back the way it came. That was a real, and real historically significant, structural property of every genuine Enigma machine, and it's one of the properties wartime cryptanalysts used to help break Enigma traffic.
What is the double-stepping anomaly this simulator implements?: It's a quirk of the real machine's mechanical rotor-advancing linkage: under a specific alignment, the middle rotor steps forward twice on two consecutive keystrokes instead of once, rather than following the simpler pattern you'd expect from an odometer-style carry. This simulator reproduces that exact mechanical behavior instead of a simplified always-one-step model.
Can I use this to actually encrypt something I want to keep private?: No — Enigma was broken during the Second World War and offers no meaningful security against anyone today, whether by hand analysis or trivially by computer. This tool is a working historical replica for learning how the machine functioned; for anything you actually need kept confidential, use a modern cipher like AES-GCM instead.
How do you decrypt an Enigma message?: Set the machine exactly as the sender had it: rotor order, ring settings, reflector, plugboard pairs and start positions. Then type the ciphertext. The reflector makes Enigma self-reciprocal, so the keystrokes that turned plaintext into ciphertext now turn the ciphertext back into plaintext on the lampboard.
How many possible settings did the Enigma machine have?: For the army machine with three of five rotors and 10 plugboard cables, 60 rotor orders times 17,576 start positions times 150,738,274,937,250 plugboard wirings comes to about 1.59 × 10²⁰. Ring settings, which that figure omits, push it higher; the settings-count section above works through the arithmetic.
Does this simulate the 4-rotor Enigma M4?: No. It models the three-rotor Enigma I and M3 with rotors I–V and reflectors A, B and C. The M4's extra Beta or Gamma wheel, its thin reflectors and the naval rotors VI–VIII are not implemented, so messages from an M4 cannot be decrypted with it.
What do Walzenlage, Ringstellung and Grundstellung mean?: They are the German key-sheet terms for rotor order, ring setting and start position. Walzenlage names which rotors go in which slots, Ringstellung offsets each rotor's wiring against its letter ring, and Grundstellung gives the window letters before the first key press. The glossary above also covers the reflector and plugboard.
Who broke the Enigma code?: Polish mathematicians Marian Rejewski, Jerzy Różycki and Henryk Zygalski first broke Enigma in the 1930s and shared their methods with Britain and France in July 1939. At Bletchley Park, Alan Turing and Gordon Welchman designed the bombes that recovered daily settings through much of the war, helped by guessed plaintext and operator mistakes.

Related tools on BrakeTools

Classical Cipher Workbench — Encrypt, decrypt, and crack classic ciphers — Caesar, Vigenère, Playfair, Morse, and more — with step-by-step visualization.
Modern Symmetric Cipher Lab — Encrypt and decrypt with AES-GCM/CBC/CTR and PBKDF2, with byte-level and process-stage visualization.

Content reviewed 2026-09-27.