The Enigma Machine

Introduction to the Enigma Machine

Arthur Scherbius, a German engineer, invented the Enigma electro-mechanical rotor cipher machine in the early 1920’s. By 1926, it was adopted by the German military.

The Enigma was a mechanical puzzle, involving several wheels, rings, and various plug connections. Each of those added to the complexity of the cipher and therefore made it more difficult to crack.

Allied Efforts to Crack the Enigma Code

Allies very quickly started to work on cracking the code. As such, they needed to know in which order the rotors were set on the machine, the start position for each rotor, the start position for each ring, and the plug settings. In total, the Enigma cipher had 10 billion trillion possible configurations, which is equivalent to a 380 bits encryption key.

With the help of the French and Polish resistance as well as the work of the British Alan Turing and the manufacture and use of “Bombes” which were mechanical computers, the allies did eventually manage to crack the Enigma Code.

Factors Leading to the Code Being Cracked

Many factors contributed to the Enigma Code being cracked, including the capture of several Enigma machines and Code Books by the allies throughout the war as well as German mistakes in using their own system. For the code to be strong, the Germans were supposed to use totally random keys. But for ease of use and speed of execution, German officers in charge of creating and updating Code Books often used simple keys such as the same letter repeated several times… Furthermore, German operators often used the same key, such as their initials, over and over again.

Paradoxically, measures and steps taken by the Germans to subsequently enhance the Code’s strength, such as not allowing any rotor to repeat their position from one day to another, and not allowing letters from the plugboard to be replaced by its neighboring letters greatly reduced the total number of possible configurations and provided shortcuts to allied cryptanalysts.

Final Crack and Impact on WWII

Enigma was finally cracked in 1941. However, Enigma traffic went dark again from February 1942 onward: The Germans had added a 4th wheel to their machines! The code was not cracked again before December 1942 and by August 1943, almost all German coded communication from the Kriegsmarine, Wehrmacht, and Luftwaffe were being read.

It is thought that the decoding of German communications shortened the war by several years!

-RBM