# Enigma Machine Simulator

> Simulate M3 and M4 Enigma rotors, plugboard and reflector to decode messages.

- Page: https://decoder.tools/enigma-simulator
- Category: Classical & Obfuscated Ciphers
- Status: live, runs in the browser
- Last reviewed: 2026-10-23

An Enigma simulator reproduces the rotor wiring, stepping mechanism, reflector and plugboard of the German Enigma machine, so that with the correct settings it decodes historical ciphertext exactly as the original hardware did.

## Example

```text Input
BDZGO
```

```text Output
AAAAA
Machine: M3 · I II III · UKW B
Letters: 5
End position: AAF
```

## What is the Enigma Machine Simulator?

Enigma is an electromechanical polyalphabetic cipher. A keypress sends current through the plugboard, then three (or four, on the naval M4) rotors, into a reflector, and back out through the rotors and plugboard to light a lamp. Because a rotor steps with every keypress, the substitution alphabet changes constantly — the same letter typed twice rarely encodes the same way.

The settings that define a message key are the rotor selection and order, the ring settings (Ringstellung), the starting positions (Grundstellung) and the plugboard pairs (Steckerbrett). Get any of them wrong and the output is noise; get them all right and the ciphertext falls out as German plaintext.

The reflector is what made Enigma reciprocal — encoding and decoding use identical settings — and also what broke it: no letter could ever encode to itself. That single constraint gave Bletchley Park the cribs that made the Bombe attack work.

## How to use the Enigma Machine Simulator

1. Select the rotor order and reflector for the machine model you are simulating.
2. Set the ring settings, starting positions and any plugboard pairs.
3. Paste the ciphertext in five-letter groups and read the plaintext.

## When to use it

- Decoding historical Enigma traffic for research or a museum exhibit.
- Teaching rotor cryptography and why the self-encipherment flaw mattered.
- Solving an Enigma-based challenge in a cryptography competition.

## Enigma Machine Simulator at a glance

| | |
|---|---|
| Models | M3 (3 rotors) and M4 (4 rotors, naval) |
| Settings | Rotor order, Ringstellung, Grundstellung, plugboard |
| Reciprocal | Same settings encode and decode |
| Fatal flaw | No letter ever encrypts to itself |

## FAQ

### Why does the same settings work for encoding and decoding?

The reflector makes the electrical path reciprocal: if A encodes to R with given settings, then R encodes to A. Operators reset to the same start position and typed the ciphertext to get plaintext back.

### What was Enigma's fatal weakness?

A letter could never encrypt to itself, because the reflector never routes a signal back to its own contact. That let codebreakers rule out crib positions instantly and made the Bombe's search practical.

### What is the difference between ring setting and rotor position?

The ring setting fixes the alphabet ring relative to the internal wiring and stays put for the day; the rotor position is where each rotor starts for a given message and was sent with it.