Simulation Panel
For our tutorial we will first focus on the Simulation panel on the left and we will select the default Enigma model, which is the Enigma I.
We earlier selected the Enigma I model, so for the three rotor slots we have a selection of five different rotors each with its own internal wiring. There are two reflectors to choose from. We will stay with the default of I-II-III and reflector B.
The wheel settings show the initial position of each rotor. On an actual Enigma machine each rotor had a thumb wheel that could be turned so that a letter would be visible through a window in the top of the machine. These settings were known as the Grundstellung. For now, leave these at A-A-A.
Each rotor had a ring setting (Ringstellung) that could be adjusted by opening the lid of the machine to access the rotors. By turning the ring on a rotor, the wiring core of the rotor is turned relative to the letter showing in the window of the Enigma machine. Leave these at A-A-A.
When a key was typed, the right-hand “fast” rotor would turn one position and this might cause the next rotor to turn if it was aligned a certain way. It is this stepping which meant the machine would not act as a standard substitution cipher but would encrypt the same letter differently on separate key presses.
The Enigma machine had an anomaly called “double-stepping” which meant that in some situations the middle rotor would step twice on successive key presses. After the tutorial, if you want to see double-stepping in action, you can set the rotors to III-II-I, the wheels to A-D-Q and the ring setting to A-A-A. Hitting a key will cause the right and middle rotors to step, resulting in the visible wheel positions to change to A-E-R. Another key press will result in all three rotors stepping to B-F-S, meaning that the middle rotor stepped twice. Not all Enigma simulators have implemented double-stepping correctly but EnigmaZone has an accurate implementation.
For now though, you should be using the default settings. If you need to get back to the default settings at any time, you can click Reset from the Options menu.
Here we have typed the letter A five times. As you can see, although a normal substitution cipher would result in an encryption to five repeated letters, e.g. QQQQQ, the Enigma machine changes the substitution for each letter. This approach made the Enigma very hard to crack.
The letters in yellow represent what would be seen through the window in the top of the machine. Each typed letter results in a turn of one or more rotors and a letter near the top of each rotor appears in each window. The Enigma worked by stepping the rotors before encrypting the letter. After typing AAAAA the rightmost wheel is showing F. If you want to see what it would look like with different initial settings, you can just alter the drop-downs for the rotors/wheels/rings/reflector and the results will be shown immediately.
As each letter is typed the path of the electric current is shown in the Display panel. After entering AAAAA the last letter A appears on the top right, representing the keyboard input, and the path going into the machine is shown in green. There are no plug board settings in this example and so A is transposed to A on the plug board (“self-steckered”). It then enters the rotors and each rotor performs a letter substitution. The small copper-coloured circles are the metal contacts for entry and exit on each rotor. The first rotor has the incoming current at contact F and the internal wiring transposes this to L. It exits at L from the first rotor and enters the next rotor at contact G. Changing the ring settings will alter the wiring in relation to the letters shown in the window. After travelling through the rotors, the reflector (in blue) transposes the incoming U to C and passes the current back through the machine, shown here by the cyan line. Eventually it passes through the plug board again and into the lamp board where a letter lights up (O in this case). As you can see, our keyboard column is also representing the lamp board.
By clicking on the formatting buttons you can separate the text into groups of four or five or you can surround the X character with spaces to make it more readable.
At the bottom of the Simulation panel you can enter the plug board connections. The original German operators would normally use ten cables to switch ten letters with ten other letters, but here we are using two settings, AT and LZ. It’s important to note that the Enigma cannot encrypt a letter to itself, and with the reflector bouncing the current back through the machine this allowed Enigma to have reversible encryption and decryption as long as the same settings are used for both.
After entering the plug board connections, the output text changes. The plug board changes a letter as it is typed, and also as it returns back through the machine and into the lamp board.
Here we have a full set of plug board settings and we have changed the choice of rotors, the initial wheel settings and the ring settings. Doing this immediately refreshes the text that was in the output box.
You can see the 185th typed character was A and it was encrypted to W. The yellow letters at the top show the final positions of the rotors as they would be seen through the lid of the machine. When the plug board received the electric current at the Y position, a plug board cable changed this to W. On our previous plug board settings you can see WY as one of the ten connected plugs.
You can drag the Display panel with the mouse or use the mouse wheel to zoom in or out.
On receipt of an encrypted Enigma message, as long as the initial settings are known, the original message can be recovered. The standard procedure on U-boats was to change the settings every day and these would be kept in a code book that would be replaced each month.