Identification group book

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The identification group book (K. Buch) had a similar cover as the aircraft reconnaissance board (F. Au. T.) shown in the picture, but in contrast to this it was not allowed to be carried on the plane for reasons of confidentiality .
Allocation list for identification groups
The swap board plan prescribed the swap board to be changed daily.

The Kenngruppenbuch (short: K. Buch ) was a secret code book that was used by the submarines of the Kriegsmarine during the Second World War to identify their encrypted radio messages and for the secret transmission of the message key . It must not be confused with the identification group booklet that was used in connection with short signals .

The identification group book of the Kriegsmarine

The Enigma key machine was primarily used to keep the communications of the Kriegsmarine wireless during the Second World War , in particular between the Commander of the U-Boats (BdU) and the German U-boats operating in the Atlantic and Mediterranean , used by the Kriegsmarine as the "key M" denotes. This was the M3 model until the beginning of 1942 and, from February 1, 1942, the Enigma-M4 exclusively for the submarines . In addition, secret code books such as short signal booklet and weather short key were used to further increase the security of the encryption and also to reduce the length of the radio messages and thus to reduce the danger of the discovery and location of the submarines by Allied radio direction finding (" Huff-Duff ") . To identify the radio messages, they were given an identification group , which was taken from the tables of the secret identification group book. The identification group consisted of a total of eight letters.

To generate them, the column numbers were taken from the identification group book according to the specification of an "assignment list for identification groups"  (image) , that is, the table area in the identification group book from which two important trigrams were to be read. These were the "key identification group" and the "process identification group". In reality, these were three letters “scrambled” as arbitrarily as possible, in this example for illustration purposes they are SKG and VKG. Each of these two trigrams was expanded into a tetragram using a filler letter . For this purpose, an arbitrary letter, for example X, was inserted in front of the three letters of the key identification group and another arbitrary letter, for example Y, was added to the back of the three letters of the method identification group. The SKG and VKG became XSKG and VKGY. These eight letters were interpreted as part of the "book groups" ( plain text ) and encrypted using a special procedure before they were sent as part of the "radio groups" ( ciphertext ) in Morse code .

For this purpose, the eight letters were written line by line in two lines and then read out column by column as four bigrams , i.e.:

XSKG
VKGY

This gave the four double letters XV, SK, KG and GY. These were individually substituted (replaced) by other bigrams with the help of the “double-letter exchange table for identification groups” , a set of separate, secret involutorial conversion tables . For example, according to the double-letter exchange table, XV became SF, SK became WI, KG became IT and GY became TA. These radio identification groups encrypted in this way were placed in front of the actual ciphertext ("initial identification groups") and repeated again at the end ("end identification groups"). A striking characteristic of marine radio messages, easily recognizable for friends and foes alike, was that the first eight and the last eight letters were identical.

Now the key machine preset according to the respective day key ( "inner key and outer key" ) was required. For this purpose, the three rollers of the machine, or the four rollers of the M4, had to be set to the basic position valid for the day , which was taken from a secret key list, for example GST. In the case of the M3, the encryptor then entered the process identification group (here VKG) and pressed the V, K and G keys one after the other. Accordingly, different lamps lit up, for example F, I and T. This was the secret key , here FIT, to which the three reels had to be set manually at the beginning of the encryption of the plain text on the sender side and at the beginning of the decryption of the ciphertext on the receiver side. In the case of the M4, there were four-digit key identification groups, procedure identification groups, basic positions and initial positions instead of the three-digit M3.

Familiar groups in the army and air force

In contrast to the Navy, in the Army and Air Force, the identification groups were not listed in a separate identification group book, but as part of the " key table ". This gave the daily key of the Enigma for a whole month, i.e. roller position, ring position and plug connections, which were changed at midnight. In addition, she listed four identification groups, each made up of three different letters, for each day.

Tag UKW Walzenlage Ringstellung ---- Steckerverbindungen ----    Kenngruppen
 31  B  I   IV III   16 26 08   AD CN ET FL GI JV KZ PU QY WX  dmr now wxy bev
 30  B  II  V  I     18 24 11   BN DZ EP FX GT HW IY OU QV RS  mrx ash djt lmq
 29  B  III I  IV    01 17 22   AH BL CX DI ER FK GU NP OQ TY  nqz avz hlr psx

The table shows an example of a key panel. Only three days of the month are shown, whereby, as was common at the time, the days are sorted in descending order. This allowed the encryptor to cut off and destroy the “used” codes of the past few days.

The sender selected any of the identification groups valid for the current day, for example for the 31st of the month "now". The identification group was used by the recipient of the message to recognize that the message was really intended for him and that it could also be decrypted with authorization. As a camouflage, the sender permuted the three letters of the identification group in any order and added two “filler letters” to be randomly changed for each radio message, for example “xy”. "Now" became "own" and finally "xyown". These five letters were placed in front of the ciphertext as the first group of five, unencrypted.

The ciphertext with a prefixed identification group was broadcast as Morse code and recorded by the recipient. He looked at the first group of five, in the example "XYOWN", ignored the first two letters and saw "OWN". He sorted the three letters in alphabetical order, got "NOW", looked in his identification group table, discovered this identification group there and could now be sure that the saying was intended for him and that he could decipher it.

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