I n 1918 a German electrical engineer named Arthur Scherbius patented his invention for a mechanical cipher machine. First developed in 1923 by his company Scherbius und Ritter, the devices went into production several years later under the newly named company Chiffriermaschinen Aktiengesellschaft. These machines, sold under the name “Enigma,” were developed for commercial use and freely available on the international market. After Scherbius’s sudden death in 1929 the company changed hands, and in 1933 the German Army acquired the manufacturing rights to the Enigma machines, which had been developed into much more complex devices since their first conception, again changing the company name to Heimsoeth und Rinke, but continuing to market the machines under the name “Enigma.” By the mid-1930s the Germany, in violation of the Treaty of Versailles, began building up its armed forces, and ordered large quantities of the Enigma-I for military use. From then on, all international and commercial sales had to be approved by the German Army.
The design of the Enigma was ingenious. Each Enigma-I machine came with a set of 5 interchangeable electromechanical cipher wheels, known as rotors. The rotors had 26 contacts on one side, and 26 pins on the other. Three rotors would be placed into the machine on a shaft, with the pins of one connecting to the contacts of the next. The rotors would then be set to pre-arranged positions, and the user would type in a plain text message on the keyboard, with the encrypted message appearing on the light panel.
(LEFT) ROTORS FROM LOT 65, THE ENIGMA-I. (RIGHT) EXPLODED VIEW OF ENIGMA-I ROTORS WITH CONTACT PINS VISIBLE.
An extra layer of complexity was added with the use of the Steckerbrett, or patch board. A series of patch cables would be plugged into the board, from 1 up to 12, and the cables, together with the rotors, would then increase the possible encoding configurations. Together with the rotors, the full complements of patch cables and the machine’s reflector, the total theoretical number of possible configurations came to the astounding figure of: 3,283,883,513,796,974,198,700,882,069,882,752,878,379,955,261,095,623,685,444,055,315,226,006,433, 615,627,409,666,933,182,371,154,802,769, 920,000,000,000 (approximately 3 X 10114 ).
DETAIL OF THE STECKERBRETT FROM LOT 65, ENIGMA-I.
The enciphered message would then be sent to the receiving party, usually via Morse code. The receiving party would decipher the message, using another Enigma machine with the rotors and cables set in the exact same positions as those of the first machine. The below video demonstrates the insertion of rotors and operation of the Enigma-I in our upcoming History of Science & Technology sale.
Fully Operational Enigma I Cipher Machine
Admiral Karl Dönitz, the commander of the Kriegsmarine’s U-boat fleet seriously doubted the security of the Enigma-I after several unexplained losses, and had the secret M4 model developed specifically for his fleet. The M4 was ready around May of 1941, and by February of 1942 all M4 machines had been distributed with the new operating procedures placed into effect.
The M4 was significantly more complex then the Enigma-I. Each machine was issued with 8 standard interchangeable rotors, the first 5 having wiring identical to the rotors issued with the three-rotor Enigma-I. While the 26 positions on the Enigma-I machine were labelled with numbers, they were labelled with letters on the M4.
(LEFT) ROTORS FROM LOT 67, THE ENIGMA M4. (RIGHT) EXPLODED VIEW OF M4 ENIGMA ROTORS WITH CONTACT PINS VISIBLE.
As with the Enigma-I, the machine would accept three standard rotors on a shaft, but in the M4, they would be paired with a narrow fourth rotor in combination with a narrow reflector. Two narrow fourth rotors, Beta and Gamma, were also issued with each machine. With the fourth narrow rotor in the "A" position, the M4 became functionally identical to and could communicate with the three-rotor Enigmas used by other branches of the military. With its stricter operating procedures and the ability to select from among 8 standard rotors and two thin fourth rotors, the M4 had a much higher level of security. Like the Enigma-I, the M4 also had a Steckerbrett, and this, paired with the four rotors and reflector, allowed the machine to produce theoretical combinations of up to: 23,276,989,683,567,292,244,023,724,793,447,227,628,130,289,261,173,376,992,586,381,072,041,865,764,882, 821,864,156,921,211,571,619,366,980,734,115,647,633,344,328,661,729,280,000,000,000,000,000 (approximately 2 X 10145 ). The below video demonstrates the insertion of rotors and operation of the M4 Enigma in our upcoming History of Science & Technology sale.
Fully Operational Enigma M4 Cipher Machine
These wonderfully complex and mathematically elegant machines are technological marvels, and remain among history’s most powerful examples of how something beautiful can be used as a devastating weapon of war.
For more on the intricate design of Enigma machines, watch this episode of By Design, presented by Bang & Olufsen.