Enigma/Simulator User Guide
If you have come to this page from the link in the Android app, you can switch between the app and this browser screen by pressing and holding the home button.
The simulator is designed to give the experience of using a real Enigma machine, as far as possible within the limitations of a flat screen. On smaller devices like phones, the layout is "scrunched up" to make best use of the space available; on bigger devices such as tablets, the spacing between the keys and indicators is more realistic.
- 1 Turning the rotors
- 2 Pressing the keys
- 3 Encrypting your first message
- 4 Decrypting your first message
- 5 Changing Simulator Options
- 6 Machine Settings
- 7 Saving and loading
- 8 The "About" screen
- 9 Sending Enigma messages
Turning the rotors
In the upper part of the machine there are 3 or 4 small windows with letters in them. These letters are part of rotating rings with all 26 letters of the alphabet written on. To change which letter is showing, push/drag the serrated wheel at the right of each letter up or down to rotate the ring and the scrambling wiring inside it.
Pressing the keys
In the lower part of the machine there is a keyboard. Pressing and holding a key does three things:
- The right-hand rotor moves round by one step. In certain positions some of the other rotors may also move.
- In the middle part of the machine one of the lamps marked with a letter lights up. This shows the enciphered result of the letter you pressed.
- The enciphered letter is also printed on a paper tape, shown just above the lamps. Only a few real Enigma machines had a printer, but we have included it so you can use it for some cool things in the simulator.
When you release the key the lamp goes out and you are ready to encipher another letter.
Encrypting your first message
Turn each of the rotors so that a particular set of letters that you choose is showing. These letters are your message key; you should remember them or write them down so you will be able to decrypt your message.
If you already have some letters printed on the paper tape, click on the tape and then select "Clear" to tear it off and start again.
Type a short message using the keys in the lower part of the machine. For real machines without a printer there would usually have been two operators, one to press and hold the keys and the other to write down which letters lit up, but you don't need to do that.
Your encrypted message is now printed on the paper tape.
Decrypting your first message
First, turn the rotors back so your original message key letters are showing in the windows. The process for decrypting a message is identical to encrypting; in cryptography terms the mechanism is reciprocal.
Now you have a choice: you can read the encrypted message letters back off the paper tape and press the keys one by one, as a real Enigma machine operator would have done, or you can take a shortcut:
- Click on the tape and select "Copy" to have the simulator remember the printed message.
- Click on the tape and select "Clear" (if you like, this is not essential).
- Click on the tape and select "Paste" to have the simulator type the encrypted message in for you.
You should see the message that you typed originally now printed on the paper tape. Success!
Changing Simulator Options
You can change some of the ways in which the simulator works. Press the "ENIGMA" logo in the upper right part of the machine to get a command menu (also available via the menu button) and select "Options".
You can turn the sound on or off here by clicking on the tick mark.
This allows you to choose which of three different Enigma machine models you want to use; the Enigma M3 has 3 rotors, the Enigma M4 and Railway Enigma have 4.
A standard way of arranging teleprinter messages was in 5-letter groups. You can choose different length groups, or no grouping.
You may have noticed that the message key of 3 or 4 letters is very short, compared to passwords you might use on web sites for example. Most of the security of an Enigma machine is provided by its internal configuration, which was typically changed by the operator at the beginning of each day. The main purpose of the message key is just to make sure that two different messages aren't encrypted with the same key, which would allow a codebreaker to try something called a depth attack.
If you want your encrypted message to be decrypted on another machine, both machines must have the same internal configuration settings. To set up the internal configuration of your virtual Enigma machine, choose "Settings" from the command menu. Depending on which model of Enigma machine you use, some of these settings may not be available:
This is part of the machine's wiring which connects the key pressed, via the scrambled wiring in the rotors, back through the rotors again and on to the lamp which is lit. On the Railway Enigma, the reflector wiring is built in to the left-hand rotor, but on the M3 and M4 the operator chooses one of the pre-wired reflectors supplied with the machine.
The rotor wheels for a specific Enigma machine model are interchangeable; each wheel has a different wiring pattern and the order of them can be changed. Some models such as the M3 and M4 were supplied with a box of extra wheels with more different wiring patterns which could also be interchanged. You can choose which wheel (numbered I to VIII) to install in which position. The left hand rotor on Railway and M4 was a special type which only fit in the left-hand position and there was only one left-hand rotor wheel available for the Railway Enigma.
Another part of the rotor settings is the position of the outer ring on which the letters are inscribed. This can be fitted in any of 26 positions which change the relationship between the letter shown and the internal wiring. The outer ring also controls when the rotor to the left moves.
Plug board pairs
The Enigma M3 and M4 models had a plug board added in between the keys/lamps and the rotors. Connecting a plug cable between two sockets exchanged the wiring for the keys and lamps of those two letters. This adds more scrambling to the mechanism and was believed to add a lot to the security (there are more details on the maths involved here if you are interested).
You can set any number of plug connections from none up to the maximum (13, where all the sockets have plugs in them) by entering the letters to be connected in pairs.
Saving and loading
"Save" and "Load" on the command menu take you to a file selector where you can save and load the current state of your machine. This includes the machine model, the internal configuration settings and the current position of the rotors (the message key, if you save at the start of your message).
There are a several save files pre-installed containing the settings and message keys for various real Enigma messages. You can delete these if you don't want them.
The "About" screen
When first installed, the simulator will show adverts on the screen alongside your machine. The "About" selection from the command menu takes you to a screen with a button you can press to make a small payment to remove the advert displays; this payment includes a donation to the Bletchley Park Trust, dedicated to preserving the site where codebreakers including Alan Turing worked to crack the Enigma codes in World War II.
Sending Enigma messages
Once you type in your message and you have the encrypted message on the paper tape, you can click on it and select the "Send" option. You will see a list of choices of apps with which you can send the message, for example email or SMS.
To decode your message, the recipient will need to know what machine settings and message key you used. There are more details on how to achieve that on the Sending and Receiving Messages page.