Enigma Machine Simulator (Rotor Cipher)
Simulate the WWII German Enigma machine in your browser, with historically accurate rotor wiring and stepping mechanics. Configure rotor selection, ring settings, starting positions, and the plugboard to encrypt and decrypt messages. All processing happens entirely in your browser.
Tips
- Enigma is a reciprocal cipher, so running the ciphertext back through the exact same rotor settings, starting position, and plugboard reproduces the original plaintext. Try it with the "Send result back to input" button.
- Changing the starting position (Grundstellung) by even a single letter produces a completely different ciphertext. In actual wartime use, this setting was typically changed every day.
- Because the signal always passes through the reflector (Umkehrwalze), a letter can never be encrypted to itself. This quirk later became a crucial clue for Alan Turing and his fellow codebreakers.
- The plugboard supports up to 10 letter pairs. The German military's own operating procedures also capped it at 10 pairs.
- Clicking "Randomize settings" lets you experience, in a simplified form, the daily key-setting ritual (changing rotors, rings, and plugboard according to a key sheet) that real operators performed every day.
Frequently Asked Questions
Side Note — The Story of Enigma and Bletchley Park
Enigma was patented in 1918 by German engineer Arthur Scherbius as a commercial cipher machine, and later became widely known after the German military adopted it to protect its communications. It combined several rotating cipher disks called rotors; each keypress mechanically turned one or more rotors, changing the internal wiring so that even the same letter typed twice in a row would usually be encrypted differently.
The effort to break Enigma began with Polish mathematician Marian Rejewski and his colleagues, who worked out the machine's mathematical structure in the 1930s. After the outbreak of World War II, a codebreaking team assembled at Britain's Bletchley Park, where Alan Turing and others developed an electromechanical device called the "Bombe" to systematically determine the daily-changing key settings. This achievement is widely credited with contributing significantly to the Allied intelligence effort.
The history of breaking Enigma leaves a lasting lesson for modern cryptographic design: no matter how sophisticated a cipher mechanism is, operational habits and human error, such as always starting messages the same way or reusing key sheets, can become a way in. This simulator is purely an educational tool for learning about that history, and should never be used to protect real communications.