enigma-rotors

Enigma coding box sells for �149 000

One of the last remaining Enigma machines has sold at auction for more than double its estimate in bidding war.

Sotheby’s said two unnamed telephone bidders had resulted in the £149,000 price tag. However, it did not trump Bonham’s record, which sold another example of the three-rotor device for £172,141 in April.

The recent Hollywood film The Imitation Game probably boosted the popularity of such machines, recounting Alan Turing’s successful effort to break the codes generated by the boxes. The Enigma machines had 159,000,000,000,000,000,000 possible settings, leading the Germans to believe it could not be cracked.  

The seller of the Service Enigma Machine (Enigma I) sold at Sotheby’s was an undisclosed European museum. The model featured thumbwheels made of Bakelite – an early plastic – rather than metal, which could have contributed to the high selling price. It is said the Nazis started using Bakelite towards the end of World War Two as their metal supplies were running out.

The Enigma Machine was patented in 1919 and was adopted by the German military services from the mid-20s onwards, although the machine and its mode of use was continually refined, so varied models of the machine for different purposes and services proliferated during the war.

Its basic mechanism can be fairly easily understood. The user takes the first letter of his plain text message and keys it into the keyboard – ‘G’, for example. Pressing the key completes an electrical circuit and lights up one of the letter lamps on the lamp-board (e.g. ‘H’): the complexity comes in the passage of the electrical signal.

The signal travels first to the plug board, which has a plug for each letter so if the machine is configured with a cable on the input letter then the signal is diverted, ‘G’ here being substituted for ‘L’. Then the signal travels up to the rotors.

There are three moveable rotor wheels, each of which has 26 positions, on the standard army Enigma, together with a reflector on the far left. As the signal passes through each wheel it goes through another substitution and the reflector enacts another substitution and then sends the signal back through the rotors a second time, so in this case the ‘L’ is transformed seven times before coming as an output which finally lights the lamp at ‘H’, which is then written down by the operator as the first letter of their enciphered message.

Pressing a key also mechanically pushes at least one of the rotor wheels – and possibly more, depending on the configuration – on one step, so if ‘G’ was pressed a second time the signal would reach a different light. Furthermore, not only could the plug board be configured in different way, and each of the individual wheels could begin a message at any one of their 26 settings, but the wheels were themselves removable and could be put in any order or exchanged for different wheels altogether.

The sequence of wheels was changed daily, so whilst the machine would always perform the same conversion with the same setting, there were a total number of 159 million million million possible daily keys.

Breaking Enigma was the work of many, including: Polish cryptographers who had already begun to decrypt Enigma traffic before the war; naval forces who risked their lives capturing Enigma machines and code books; Alan Turing and other mathematicians with their revolutionary models for deciphering; and Tommy Flowers and other mechanical geniuses who designed 'Colossus', the world's first programmable computer.

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