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SIGABA Machine Simulator

Explore SIGABA encryption and decryption with an educational 15-rotor model in your browser — free, with no sign-up. Set the 15 wheels across three banks, enter your message and follow the signal trace. The starting key is restored for each message.

Machine setup

Set the 15 wheels in three banks. The same starting key is restored for each message.

Variant

CSP-889CSP-2900

Cipher wheels

0:O · 1:O · 2:O · 3:O · 4:O

Control wheels

5:O · 6:O · 7:O · 8:O · 9:O

Index wheels

0:0 · 1:0 · 2:0 · 3:0 · 4:0

Encrypt or decrypt

Choose the same starting key and variant to decrypt. SIGABA has no reflector; decryption runs through the cipher wheels in reverse.

EncryptDecrypt

Plaintext0 / 5000

Ciphertext

Group ciphertext in fives

Historical keyboard rule: plaintext spaces become Z before enciphering, and plaintext Z becomes X. Decryption prints an internal Z as a space, so an original Z cannot be recovered.

Follow the signal

The current letter passes through five cipher wheels first. Control and index pulses then choose which cipher wheels advance for the next letter.

Enter text to inspect each letter's path and wheel movement.

Educational CSP-889 / CSP-2900 model. The published 26-contact wheel wirings are simulator reconstructions, not verified wartime wirings; known historical ciphertext cannot be decrypted here without its matching wheels and key.

All processing stays in this tab. Messages and key settings are never sent to mtool. Historical rotor ciphers are unsuitable for modern secrets.

Mechanics, wiring provenance, and test vectors: NSA · SJSU · Rotorvis

How it works

Configure all 15 wheelsSet the 15 wheels in three banks. The same starting key is restored for each message. Selecting a wheel already in another slot swaps the two IDs. Each 26-contact wheel is used once across cipher and control banks.
Encrypt or decryptChoose the same starting key and variant to decrypt. SIGABA has no reflector; decryption runs through the cipher wheels in reverse. Historical keyboard rule: plaintext spaces become Z before enciphering, and plaintext Z becomes X. Decryption prints an internal Z as a space, so an original Z cannot be recovered.
Follow the signalThe current letter passes through five cipher wheels first. Control and index pulses then choose which cipher wheels advance for the next letter.

Questions

What is the SIGABA machine?

Simulate SIGABA online: configure all 15 rotors, encrypt and decrypt with CSP-889 or CSP-2900, and inspect the irregular stepping. Educational wiring is disclosed. The American machine was also called ECM Mark II (M-134-C). Five 26-contact wheels transform the message from left to right. CSP-2900 reverses the motion of slots 2 and 4.

How do the 15 SIGABA rotors work?

Five 26-contact wheels drive irregular cipher-wheel stepping. Slots 1 and 5 stay still; slot 3 moves every keypress. Five 10-contact wheels never step during a message. They route control pulses to cipher wheels. The current letter passes through five cipher wheels first. Control and index pulses then choose which cipher wheels advance for the next letter.

How do I decrypt SIGABA ciphertext?

Choose the same starting key and variant to decrypt. SIGABA has no reflector; decryption runs through the cipher wheels in reverse.

What happens to spaces and the letter Z?

Historical keyboard rule: plaintext spaces become Z before enciphering, and plaintext Z becomes X. Decryption prints an internal Z as a space, so an original Z cannot be recovered.

Are these the original wartime rotor wirings?

Is this tool free?

Yes. This tool is free, with no sign-up and no daily limits.

Do I need an account?

No. You can use this tool without an account.

Is my input sent anywhere?

No. This tool runs in your browser. Your input and results never leave your device unless you choose to share them.