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Operation of the Enigma machine with an example

Basic handling

After preparing the setup for the machine (wheel numbers, wheel order, ground setting, ring setting, plug) scrambling messages is very simple: You press a letter of your plain text and a lamp indicates the enciphered letter. You write down this scrambled letter and press the next one.....

The Enigma machine is symmetrical, the enciphering and deciphering method is the same. For decoding of the message the setup must be equal. The ciphered text is typed in and the plain text comes out.

Basic functionality




The heart of the Enigma is the rotor wiring. Each rotor has 26 spring loaded terminals on its right side and 26 flat circular terminals on its left side. The terminals are arranged in circular mode. Each rotor has different fixed internal random fashioned wiring from the left side to the right side of the wheel. Each terminal carries the name of a letter from A to Z (sometimes also numbered from 1 to 26). These letters are arranged on a ring outside and can be seen through the windows of the machine. But the Position of the ring can also be moved in relation to the rotor wiring (ring setting). Each time a letter is pressed, the right wheel moves on one of its 26 places. Once during 26 moves, at the turnover position on right wheel, the middle wheel also moves one place. If the middle wheel reaches turnover position, the last wheel moves, too. The turnover is done by mechanical mechanism using a 'T' shaped pushrod ( ) and notches.

This diagram shows how that works:


Electrical diagram


If a key is pressed, the current flows from the battery through the pressed key contact to the corresponding plug, to the entry wheel and passes the three wheels from right to left. After passing the reversing wheel (reflector), the current flows back through the rotor wiring from left to right, back to the entry wheel, plugboard, keyboard to the lamps. And one lamp lids. Then the current goes back to the battery.

If no cable is connected to the socket of a letter, the two sockets of the letter are connected by a hidden spring. This is called ``self steckered''. If a plug is plugged in, the springs are forced away and new connections are made through the socket and the cable (see electrical wiring diagram).

This wiring does not allow that a letter enciphers to it's self. A D will never become a D. And this was one of the main weak sides of the Enigma machine.


This a ciphered text:


The first line is the setup.

215 rotor order (Walzenlage) means left wheel number 2, middle wheel number one and right wheel number 5.

AAA is the corresponding ring setting (Ringstellung).

FRA is the corresponding starting position (Grundstellung).

AB IR UX KP Plugboard connections (Steckerverbindungen).

And this is the enciphered plain text.


Types of Machines

There are different types of Enigma machines.

Enigma D, for non-military use

Has four wheels and no plugboard.

Model M3

It has three wheels from five possible wheels (I-V).

It was used by the german Airforce (Luftwaffe) and Forces (Wehrmacht).

Model M4

It has three wheels of eight (I-VIII) and two fourth wheels (called \( \beta \), \( \gamma \)) and two reflectors (B, C). The fourth wheel does not change position during enciphering and had a fix position on the left side in the Enigma.

M4 was used by the German Navy after 1943 (before they also used Model M3)

next up previous contents
Next: How secure is the Up: Enigma - a very Previous: What is the Enigma   Contents
Martin Oberzalek 2000-04-04