Enigma M3: Naval Cipher
The Navy wanted more than the Army’s machine gave them, so their Enigma came with a bigger box of rotors.
The M3 is the same three-rotor frame, but it came with rotors VI, VII and VIII on top of the Army’s five: eight to choose from for three slots. The three new ones also have two turnover notches each instead of one. That sounds like a small change, but it multiplies the number of possible keys, and it made naval traffic a lot harder to read than the Army’s.
Like the others, M3 is a working machine rather than an animation. Press a key and the rotors step, the current runs through the plugboard, the rotors and the reflector and back by a different route, and a lamp lights. Historical wiring, historical notches, historical stepping. Encipher something, wind back to the same ground setting, type the ciphertext in, and your original comes back. The machine undoes itself.
Type straight into any app#
Switch to the Enigma keyboard in Messages, Mail, Notes, or anywhere else you type, and every letter is enciphered as you press it. The app you’re in only ever gets ciphertext. A strip above the keys shows what you actually wrote, since the text field never sees it.
Set it like a signals officer#
The key sheet carries a month of daily keys: which rotors in which order, ring and ground settings, and the plugboard pairs. Tap the day and the machine is set, the way it was done from a printed sheet on a plotting table.
What’s here#
Rotors I–VIII, reflectors B and C, and a thirteen-cable plugboard
The Enigma keyboard, for enciphering inside any other app
A month of daily keys, generated from a seed you can share
Share sheet support to encipher text you’ve already written
Home Screen and Lock Screen widgets carrying the day’s key
Shortcuts and Siri actions for enciphering and deciphering
A network of your own#
To read each other’s signals, two people need the same key sheet, just like two ships needed the same printed one. Share yours by AirDrop, or hand it straight to a nearby device. It never touches a server, because there isn’t one.
A note on history#
I built this because the engineering is fascinating, and so is the maths that eventually beat it. The machine served a regime that used it to wage war. What interests me is how it worked, and how it was beaten.
Privacy#
Enigma M3 doesn’t collect anything. No analytics, no tracking, no advertising identifier, no account.
Nothing you type goes anywhere. Signals are enciphered on your device and stay there. Key sheets are made on your device too, and when you share one it goes straight to the device you choose. It never passes through a server of mine, because I don’t have one.
The keyboard has no network access and doesn’t ask for “full access”.
Support#
Mail support@backslashed.se and I’ll get back to you.
It helps to know which device and iOS version you’re on, what you expected, and what happened instead. If a signal wouldn’t decipher, include the rotor order, ring setting and ground setting.