Grid key 44

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The grid key 44 (short: RS 44 ) was a manual key method used by the German Wehrmacht from March 1944 during the Second World War . The grid key replaced the previously used double box key .

history

While the Enigma was used at middle and higher command levels of the Wehrmacht, such as division staffs and higher, the lower (mostly advanced) command staffs, such as company or battalion staff , had no key machines. They used manual key procedures that allowed manual text encryption “with paper and pencil”. From 1941 the double-box key was used in the army .

In view of the constant threat of an Allied invasion in the West, increased security awareness and the need to be able to communicate secretly with advanced command posts, the encryption department of the Wehrmacht High Command introduced the Army and Air Force code 44 in March 1944 .

Procedure

In contrast to the previously used double box key, which was a monoalphabetic bigraphic bipartite substitution, the grid key 44 was a transposition method . The relevant (at that time secret) service regulation "Key Instructions for Raster Key 44 (RS 44)" of March 27, 1944 speaks of an "offset procedure". This means that the letters of the plain text were not substituted (replaced) by secret letters, but the sequence of letters was transposed ("offset").

For this purpose, a daily changing grid template was used, which “contains black and white fields (blank and writing fields) in an irregular arrangement.” The templates comprised 24 lines and 25 columns. In each line there were ten white fields, the so-called writing fields. Starting at any point in the grid, the plain text was entered line by line , with only the white fields being used and the black ones being skipped. Then the ciphertext was read out column by column .

It was important to tell the authorized recipient of the message the point in the grid at which the entry of the plain text began. The location of this field, known as the "starting field of the saying", was encrypted in the message header. For this purpose, the coordinates of the start field were read by the encryptor at the edge of the template, first the column and second the line. All columns and lines were irregularly but clearly identified by a pair of letters between “aa” and “ee”, the so-called “column solution” or “line solution”. For example, at the top of the grid it said: 

cb ea ac ba db ab ed cc dd bd ee ae de aa eb be ce dc bb ad da bc ec ca cd

If, for example, the plain text was entered in the tenth column, then the encryptor read the column solution “bd”. In an analogous way he received, for example, "ca" as the line slogan. This resulted in the sequence of letters “bdca” as the “clear ” slogan key (ie as the coordinate of the initial field of the slogan). This was encrypted with the help of a "letter exchange table", which was located on the back of the grid, also changed daily, and looked like this, for example: 

a b c d e
o s u m v
z r b k h
w y f p d
t i e n a
c x q l g

Five different homophonic substitutes (replacement letters ) are available for each individual letter of the clear saying key . The encryptor had to select one of them as arbitrarily as possible. As a result, he received the “secret” spelling key, here for example “ykqo”.

The encrypted slogan key (secret slogan key) was entered together with the time ("tactical time") and the number of letters of the slogan as a slogan header in a slogan form. In the example, the message header looks like this if the text was encrypted at 10:20 p.m. and was 108 letters long: 

2220 - 108 - ykqo

As further important information, the authorized recipient of the message had to be informed of the column in which the reading of the text from the grid began. For this purpose, the cross-sum of the individual digits, the number of minutes, the time and the length of the message was formed, here 2 + 0 + 1 + 0 + 8 = 11. Correspondingly, the column-by-column reading now began eleven columns to the right of the tenth column arbitrarily selected above for entering the plain text, so here in column 21. On October 18, 1944, this rule (which was probably too complicated for practice) was dropped and the key operator then freely chose the read-out column, with the stipulation not to choose the column of the initial field. The readout column was communicated to the recipient of the message using two additional letters in the headline. These were the homophonic encrypted column solution of the same via the letter exchange table. In the case of column 21 with column solution (see above) "da", for example: 

2220 - 108 - ykqo pz

After all secret letters had been read out completely from a column, the next column to the right of it was always continued, with the first (column 1) following the last column (column 25). The text encrypted in this way was usually transmitted as a secret message in Morse code as groups of five by radio and could be unambiguously decrypted by the authorized recipient, who was in possession of the valid daily key, reversing the procedural steps.

literature

Web links

Individual evidence

  1. ↑ Friedrich L. Bauer: Deciphered secrets. Methods and maxims of cryptology. 3rd, revised and expanded edition. Springer, Berlin et al. 2000, p. 102.
  2. ↑ Friedrich L. Bauer: Deciphered secrets. Methods and maxims of cryptology. 3rd, revised and expanded edition. Springer, Berlin et al. 2000, p. 68.
  3. ↑ Michael J. Cowan. Grid Key 44 - The Epitome of Hand Field Ciphers . Cryptologia, Vol 28 (2), April 2004, p. 115
  4. ↑ a b High Command of the Wehrmacht: Key instructions for grid key 44 (RS 44) . Ag WNV / Fu I No. 3000/44 go., March 1944, p. 4
  5. ↑ High Command of the Wehrmacht: Key instructions for grid key 44 (RS 44) . Ag WNV / Fu I No. 3000/44 go., March 1944, p. 11