![]() ![]() They required the operator to key in the message key letters twice in succession and transmit the six letters that resulted. The lamps that lit (the encipherment) were then also sent in the message preamble.īut the Germans made a bad mistake in devising this system. Then the operator keyed in one after another the three letters actually to be used for the start of the message. There were different systems used by different forces at different times, but we will describe the simple system used before the war by the German Army and Air Force.įirst, with the machine in the base configuration, the rotors were turned to a start position selected by the operator but sent in clear in the message preamble. The method for this was to use the Enigma machine itself to encipher this crucial part of the message key. The principle was that this should be a different start position for every message sent. Now what remains is for the sender to choose, and then convey to the recipient, a rotor start position. U to A, and so on.įor the moment we can ignore the last section (the Kenngruppe) which was used in various different ways at different times by the German armed forces.īoth sender and intended receiver have identical copies of the setting sheet and so both can put their machines into exactly the same 'base position' for a given 24-hour period. There are ten pairs of letters and the two-pin plugs at each end of a piece of wire are plugged into the letter sockets given, i.e. Next come the Steckerverbindungen or plug connections. The setting sheets says that the ring on the left hand rotor should be turned until 6 (letter F) is by the catch, 20 (letter T) on the middle rotor and 24 (letter X) on the right hand rotor. The next three numbers are the ring settings. On the top line, the day 31 is followed by the rotor order for assembling the rotors on their shaft, in this case: I V III. The sheet shows a line of entries for each day in the month. Geheim! Secret indeed! This is an example of the setting sheets used: This was achieved by pre-printing setting sheets - a month's settings on one sheet, which was distributed by courier. The Germans, following Scherbius's original sugestions, decided to specify exactly everything except the rotor start position for each 24-hour period. This is of Tony Sale's sequence of pages on the Enigma, explaining how the Enigma was used in German military practice, and outlining the problem facing anyone trying to break the system.Īs mentioned on page 1 of this sequence, the message key, (the complete and exact configuration of the machine in its starting position), had to be conveyed to the intended recipient of the message. The Enigma - 3 Military Use of the Enigma ![]()
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