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My interest in radio communications, electronics and computer programming, plus a talk with the curator of a museum, has led to an interest in a family of what is perhaps the world's best known crypto device - but definitely not the most secure: the Enigma.

Background information on the invention of the Enigma

Enigma was originally the name of a crypto device, patented in 1919 by the Dutchman Hugo Alexander Koch, who constructed one of the worlds first electromechanical machines for encryption and decryption (a.k.a. coding and decoding).
Before WWI, coding messages in such a way that only the recipient could read, was all handwork. A few devices were invented to help, but the codes they produced were not very secure Note 1. People make mistakes, and coding messages by hand takes time.
In the early 1900s, electricity found its way into homes and offices, and the speed and volume of communications went up rapidly after the installation of networks including telegraph, telephone, and radio (or 'wireless', as it was called at that time). Unlike letters, messages sent over a telegraph line or via a radio link cannot be packed in an envelope, and anyone who has access to the line or who has a radio receiver, can read everything, without being noticed himself.
Mr. Koch thought his invention could be sold to banks to make secure transactions over a regular telephone or telegraph channel, but found no interest for his Enigma machine. The Dutch government didn't show any interest either, and continued using code books for their secure communications. After a few years, the patent went to Arthur Scherbius, the German founder of the factory "Chiffriermaschienen AG", that sold most of its products to the German government. This factory would exist until 1935. Enigma machines made at a later date, were produced by several different manufacurers.

Operating principle of the Enigma machines

The Enigma machine is so simple, that it is hard to imagine the vast number of codes it can produce.
The basic cryptographic operating principle is that of substitution Note 2.
All machines have a typewriter keyboard, a set of 'rotors' or 'Walzen', and a lamp board, with a layout similar to the keyboard.
Electrically, each key is connected to a battery when pressed, and to a lamp with the corresponding letter of the key when released. The contacts coming from the keys are connected to a ring of contacts (usually 26), called the 'entry rotor', at the right hand side of the rotor set Note 3. Each rotor has 26 contacts on each side, and 26 wires leading from one side to the other, but the contacts are not wired in the same order on both sides.
On the left hand side, a 'reflector' or 'Umkehrwalze' has 26 contacts, and 13 wires that connect one contact to another, in no obvious order. The rotors plus the reflector act like a bundle of 13 wires that connect each of the 26 contacts to another (always to another, never to itself!). The way the contacts are connected, change as soon as one or more of the rotors turn. And this is precisely what the machine does: each time a key is pressed, the rotor on the right advancess one step. One or more notches on the rotor can cause the next rotor to turn one step at the same time Note 4. Later versions have an additional plugboard or 'Steckerbrett' to change the wiring order on the entry rotor.
One of the interesting features of this machine is that encryption and decryption are done the same way. If, for a given device setting, the letter G is wired to the letter A, the letter A is wired to the letter G. If you encrypt a message, and reset the rotors to the original starting position, you can type the encrypted message and the output will be the original input textNote 5.

My own "Schluessel G" Enigma simulator

In 2001, when I was looking for information on the Enigma machines, there was no simulator for the "Schluessel G" machine I had seen in the museum. This model has been sold commercially in the lat 1920s, and was used before and during WWII by the German Intelligence Service ("Abwehr") as well as the Dutch Royal Navy ("Koninklijke Marine").
I decided to make a simulator that looked somewhat like the original machine, and I wrote a few lines of code in Javascript. The simulator should work on every browser that supports Javascript.
It is wired similar to the G-312, the Abwehr model on display in the museum at Bletchley Park, and I tested it for compatibility. I have included a small glossary at the bottom of this page.

Go to the Enigma Schlüssel G simulator.

More information about the Enigma

Enigma simulators
WWII Codes and ciphers
Bletchley Park - Station X
CSG: the Crypto Simulation Group
David Hamer's homepage - David's information was very useful when building my simulator


Grundstellung: Starting position, as read through the windows from the rings of the rotors.
Ringstellung: Ring setting, the alignment between the electrical wiring in the core and the mechanical stepping at the ring of a rotor.
Walzenlage: Rotor position, the order in which the rotors, numbered I, II and III for the "G" Model, were placed from left to right in the machine.

Note 1:
One of these devices that survived in its basic form from the 15th century to 1942, is the M-94. This type of device was re-invented several times in history. The first person to write about it was Leo Battista Alberti (1404-1472).
It consists of a large bolt or spindle, that holds a a set of numbered disks, with the 26 letters from the alphabet written in a different order on the rim of each disk. The key is the order in which the disks are placed. The secret message is set on one line, and any of the 25 other lines was sent as the secret message.

Note 2:
There are two principal cryptographic operations: transposition (changing the order of the letters in the message) and substitution (replacing every letter in a message by another one). Both operations can be combined for enhanced security.

Note 3:
'entry rotor' is a somewhat misleading name, since this contact ring was not rotating, but was fixed to the chassis.

Note 4:
This is true for most machines, some early models may have stepped in a different manner, using a comb mechanism.

Note 5:
As you can see, there is no space bar. The letter X was used for space, and some other letters were used for common combinations of letters, like "sch". Numbers were written down, e.g. number 7 was typed as "sieben".

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