Enigma watch
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The Enigma clock (also: plug clock or device EU ) is an additional device to the Enigma , i.e. the rotor key machine with which the German military encrypted their radio messages during World War II .
The "clock" was introduced by the German Air Force as an addition to the Enigma I on July 10, 1944 . Similar to the plug board of the Enigma, it causes the letters to be swapped before and after the set of rollers in the key machine .
service
The clock was connected to the Enigma's plug board with the help of twenty pairs of cables. The exact procedure was described on a sticker "Please note!", Which is located on the inside of the case cover of the watch:
- Hang the Enigma clock on the right of the Enigma box.
- Establish plug connections, 1a and 1b equal 1 plug connection.
- Follow the sequence 1a-1b, 2a-2b to 10a-10b and insert from left to right according to the key documents.
Depending on the applicable daily key , the clock had to be connected to the sockets on the front panel of the Enigma. The following table shows an example of an excerpt from a (then) secret " key board " in which the plug connections were also specified. For example, for the 31st of the month these are AD, CN, ET, FL, GI, JV, KZ, PU, QY and WX.
Tag UKW Walzenlage Ringstellung ---- Steckerverbindungen ---- 31 B I IV III 16 26 08 AD CN ET FL GI JV KZ PU QY WX 30 B II V I 18 24 11 BN DZ EP FX GT HW IY OU QV RS 29 B III I IV 01 17 22 AH BL CX DI ER FK GU NP OQ TY
When using the clock, the plug connections - unlike usual - were not to be plugged into the plug board of the Enigma with the help of ten double-pole cables, but the sockets of the plug board were to be connected to the clock. Twenty double-pole cable cords were used for this, which were connected to the clock on one side and which were plugged into the Enigma's plug board with double-pole plugs on the other. Ten of the cable plugs are marked red and the other ten are marked white. The upper socket of a socket pair on the Enigma connector board has a slightly larger diameter (4 mm) than the lower one (3 mm), and the clock's cable plugs also have different diameters so that they can only be inserted in one orientation.
When inserting the connections according to the key document, the following sequence had to be observed. First, the red marked first double plug (1a) of the clock was plugged into the double-pole socket of the Enigma, which was mentioned as the first in the daily key, so in the example considered "A". The white double plug (1b) was then to be plugged into the socket for the second letter, here “D” and so on up to the tenth pair. According to the key board, the last pair was the red plug (10a) in the “W” socket and the white (10b) in the “X” socket on the Enigma plug board.
function
Inside the clock, the letters are swapped with the help of two concentric rows of contacts, each consisting of forty contacts, arranged in a circle, which were wired in pairs according to a fixed scheme (abbreviations: ws = white, rt = red). This assignment can be shifted one position at a time using a rotary switch (in the middle) of the clock. The following assignment applies to position 00 of the rotary switch:
Ausgang (ws) Uhrkontakt (ws) Uhrkontakt (rt) Eingang (rt)
07b (dick) 00 00 01a (dick)
01 01
07b (dünn) 02 02 01a (dünn)
03 03
01b (dick) 04 04 02a (dick)
05 05
01b (dünn) 06 06 02a (dünn)
07 07
08b (dick) 08 08 03a (dick)
09 09
08b (dünn) 10 10 03a (dünn)
11 11
06b (dick) 12 12 04a (dick)
13 13
06b (dünn) 14 14 04a (dünn)
15 15
02b (dick) 16 16 05a (dick)
17 17
02b (dünn) 18 18 05a (dünn)
19 19
09b (dick) 20 20 06a (dick)
21 21
09b (dünn) 22 22 06a (dünn)
23 23
05b (dick) 24 24 07a (dick)
25 25
05b (dünn) 26 26 07a (dünn)
27 27
03b (dick) 28 28 08a (dick)
29 29
03b (dünn) 30 30 08a (dünn)
31 31
10b (dick) 32 32 09a (dick)
33 33
10b (dünn) 34 34 09a (dünn)
35 35
04b (dick) 36 36 10a (dick)
37 37
04b (dünn) 38 38 10a (dünn)
39 39
The contacts inside the watch, designated here as “white” (ws) or “red” (rt), were connected to one another in a seemingly random (then) secret way according to the following scheme:
Uhrkontakt (ws) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 Uhrkontakt (rt) 26 11 24 21 02 31 00 25 30 39 28 13 22 35 20 37 06 23 04 33
Uhrkontakt (ws) 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 Uhrkontakt (rt) 34 19 32 09 18 07 16 17 10 03 08 01 38 27 36 29 14 15 12 05
The rotary switch (in the middle) of the clock has forty positions (00 to 39). The assignment given in the table (above) is shifted accordingly by one position. Each position of the switch causes a different exchange of the twenty letters that were wired between the clock and the plug board. The remaining six letters of the alphabet remain “unplugged” and are not swapped.
use
Unlike the Enigma's plug board, which always produces an involutorial permutation , the letter permutations caused by the clock are noninvolutorial . This has great cryptographic advantages and makes the Enigma with a clock much more resistant to deciphering attacks than without a clock. However, it was only used sporadically by the Air Force - presumably due to production bottlenecks caused by the war.
The internal wiring of the watch is designed in such a way that an involutive permutation is generated in every fourth position of the rotary switch, while it is non-involatory in all other positions. In position “00” of the rotary knob, the interchanges are identical to the external plug connections.
The position of the rotary switch to be set had to be communicated to the authorized recipient of the encrypted radio message separately from the daily key. This was done in the first few weeks of using the clock by specifying the number expressed in words that described the position of the rotary switch, i.e. an entry between ZERO (00) and DREINEUN (39). From November 2, 1944, the position of the rotary switch was coded in the form of four letters. Here, two alphabets were used, which are indicated on a plaque inside the housing cover.
Alphabet I
0 1 2 3
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Alphabet II 0 1 2 3 4 5 6 7 8 9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
For example, if you want to code the switch position "39", you use a replacement letter from alphabet I for the first digit, ie "3", and a letter from alphabet II for the second digit, ie "9". To protect against transmission errors each digit is coded twice in a row, i.e. doubled. "39" becomes "3399" and then, for example, "TZXY". The recipient can translate this back into "3399" with his two identical alphabets and then knows that he has to turn the switch to position "39" to decrypt.
The security of the encryption has been significantly improved by using the watch. It is important that, in contrast to the plug board of the Enigma, the permutation through the clock is non-intrusive. While this does not lead to an overall nichtinvolutorischen operation of the Enigma - this continues to be in involution - but after all, is Involutorik of the connector board removed. In this way the Germans succeeded (albeit without knowing it or even suspecting it) to outsmart a large part of the British methods developed in Bletchley Park during the war for deciphering the Enigma. For example, the diagonal board developed by Gordon Welchman (German: "Diagonal board ") presupposes the involutorics of "plugging". Since this was canceled by the clock, the diagonal board was suddenly ineffective.
Decipherment
The many mistakes the Germans made in handling their key machines allowed the British code breakers in Bletchley Park to break into this encryption method, which was strengthened by the clock. One mistake was that the Luftwaffe did not introduce the watch suddenly and across the board, but only used it sporadically in a few key circles. In addition, many key circles remained without a clock. In addition, radio messages were encrypted and sent with the same letters using the different methods. Since the British code breakers were already routinely deciphering radio messages that were encrypted with the Enigma without a watch, they were able to reconstruct the rigid functioning of the watch through the ciphertext-ciphertext compromises at hand. There were only forty different permutations that the clock could bring about. In this respect it was a fixed procedure which was superimposed on the Enigma and which could therefore easily be stripped off by the English after they had recognized and reconstructed the method. After that, their usual, tried and tested deciphering methods were used again.
literature
- Arthur O. Bauer: Radio direction finding as an Allied weapon against German submarines 1939-1945 . Self-published, Diemen Netherlands 1997, ISBN 3-00-002142-6
- Friedrich L. Bauer : Deciphered Secrets. Methods and maxims of cryptology. 3rd, revised and expanded edition. Springer, Berlin a. a. 2000, ISBN 3-540-67931-6 .
- Philip C. Marks : Reversing roller D: Enigma's rewirable reflector . Part I. In: Cryptologia , 25 (1), 2001, pp. 101-141.
- Stuart Milner-Barry : BP's Notes on the Enigma Clock . Bletchley Park, 1944. cryptocellar.org (PDF; 1.5 MB; English) accessed February 16, 2016.
- Michael Pröse: Encryption machines and deciphering devices in World War II - history of technology and aspects of IT history . Dissertation Leipzig 2004, pp. 40–41, tu-chemnitz.de (PDF; 7.9 MB)
- Heinz Ulbricht: The Enigma cipher machine - deceptive security . A contribution to the history of the intelligence services. Dissertation Braunschweig 2005, pp. 11–13, tu-bs.de (PDF; 4.7 MB)
- Heinz Ulbricht: Enigma clock . Cryptologia 23 (3), 1999, pp. 193-205.
- Heinz Ulbricht: The Enigma clock . In Hugh Skillen (Ed.): The Enigma Symposium . Bath, 2000.
Web links
- Photo of an Enigma with a clock
- Simulation program of the Enigma with clock (English)
- Enigma clock in the Crypto Museum (English)
- Enigma accessories (English)
