An encryption method of the German Wehrmacht with plenty of interesting characteristics regarding eg. avoiding cryptanalytical attacks.

For Klaus Schmeh’s Crypto Kolumne, I wrote a quick summary in English – based on original, formerly under death penalty secret files (even regarding its correct application..) from 1944:

http://www.cdvandt.org/RS44.pdf

To know the method is a must, imo, as it represents sort of a bridge between classic encryption and Enigma. It simultaneously (!) combines multiple differing encryption steps (while Enigma uses all steps the same – rotors) and even adds additionally inclosed double encryption for eg numbers and cities. To understand how the Rasterschlüssel 44 works, opens a lot of understanding in cryptology.

The method itself, imo, is genius. Guess the Britains would nowadays not discuss Brexit if the Germans had combined it with Enigma additionally..

QT

ZURÜCKTRETEN DREI IN FRGT BEENDET WIE BEFOHLEN STOP VERLUSTE BEGRENZT STOP UMGRUPPIERUNG IN AA WQFNTC KORRE WQFNTC KORRE EE VERMUTLIQ UM EINS AQT UHR BEENDET

(Fallback three in Frgt finished as ordered – stop – Losses limited – stop – Redeployment in aa wqfntc korre wqfntc korre ee probably at one eight o’clock finished) frgt = fragments?

– City name ‘wqfntc korre’ without monoalphabetical table is here unsolved

– Daily changing crossword checkerboard patterns (similar to one time pad method)

– checkerboard is put below transparent paper

– encryption: writing in LINES in white fields, then reading the COLUMNS as the decrypted text

– decryption: writing in COLUMNS in white fields only, then reading the LINES to get the cleartext

(due to the different structures of the checkerboard, the letters are shuffeled according to it’s unique shape)

– min 60, max 200 letters. Larger messages must be split, shorter messages must be filled up with (useless) selection words of different length with different starting letters, no military meaning etc. neither repeating the message text itself, eg …MESSAGEPOTATOESHOECOLDNESS

– locations / city names must be double encrypted (additionally, monoalphabetic) with separate monoalphabet code. Start of this double encryption signalled with aa (anfang) and end with ee (ende), monthly change of this monoalphabetic code. City names have to be written twice, eg AA IGKALFISI IGKALFISI EE reading as aaigkalfisiigkalfisiee..this City is Orjechow.

– single letter coordinates eg. A89 as ANTON AQT NEUN, except Y which must be written as IPSILON instead of YPSILON

– Same with CH which is Q, eg. AQT instead of the German word ACHT

– Abbreviations, if non-misunderstandable explicitly shall be used, even if the amount of 60 letters must later be filled up with selection words

– Use X to separate, only if necessary use STOP (. Punkt); KOMA (, Komma); FRAQ (? Fragezeichen); KLAM (( KLAMMER)

– Forbidden is the use of multiple 0’s, thus 00 is ZENTA, 000 is MILLE, 0000 is MIRIA, eg 5000068 is FUENF MIRIA SEQS AQT or 00700 is ZENTA SIEBEN ZENTA, roman numbers with ROEM in advance

– Transposition of departments allowed, eg ‘3. Panz. Grd. Rgmt. 10’ into ‘3. Grd. Rgmt. Panz. 10’

– Hours/Minutes are separated with X eg. 00:00 pm is written as ZENTA X ZENTA UHR, thus also no repeating 00’s and always the word ‘UHR’ (o’clock) afterwards to avoid misunderstanding, eg in military context with coordinates

– Messages shall be sent at different times a day, not contain repetitions and in case of errors made be written as a completely new text

– METHOD is the ‘Rasterschablone’ (checkerboard) consisting of 24 lines, 25 columns. In each line is 10 white writing fields. On top of the checkerboard is – on a daily basis – the ‘Spaltenlosung’ (column pattern) containing one bigram from letters a to e for each column as well as aside the checkerboard the ‘Zeilenlosung’ (row pattern), also containing such bigram for each row.

– the ‘Schlüsselblock’ (keycode notebook) contains transparent paper with lines exactly matching the shape of the ‘Rasterschablone’

ENCRYPTION
– Start to write at any white field of the checkerboard, continue until end and if required start from the top again

– Where the message starts (first field) is the ‘ANFANGSFELD DES SPRUCHES (starting field of the message). Read the bigrams from the top as well as side of the checkerboard and you get the KEY, eg ‘ab cd’ which tells the reader where to start ‘reading’ the message from the checkerboard. Also black fields can/shall be used as starting field, reading/writing then starts from the next white field to the right.

(now we can see that with one checkerboard but daily changing column/row patterns, the messages when transmitted being first read vertically instead of horizontally can be a very safe method: Two encryptions simultaneously:

– SHAPE of the checkerboard (text being read vertically but influenced by the shape), similar to Grille ciphers
– KEY for the starting field, influenced by the daily column/row patterns..but even more to come..)

– the key for the starting field, eg. ‘ab cd’, has to be encrypted as well. This according to a daily (!) one time pad, eg
a = g e b z l
b = t q x u r
c = a f o k w
d = c i h s m
e = d y n v p
so the key for our starting field can eg. be encrypted as. ‘zx km’.

– All key bigrams used from the column/row pattern atop/aside the checkerboard must be crossed out once (still readable) by the encryptor after use, then twice by second use and shall not be used after being crossed out twice (separately) as long as there are still other bigrams available (‘Es ist verboten.’ – it is forbidden). No preferences regarding letters shall be chosen, no letter repeating in tge key, thus key always consists of four different letters.

(by this, the full use of the methods’ encryption power is secured..)

– now, it would be way too easy to start transmitting the message beginning from its starting field, thus: the message starts with a ‘Spruchkopf’ or head of the message consisting of TACTICAL TIME, LENGTH OF MESSAGE and KEY. Example: ’04:17 78 zx km’. We now take these MINUTES as well as the amount of letters and calculate its CROSS SUM, thus 1+7+7+8=23. From the starting field (or row ‘ab’), without counting its column, we then count 23 columns to the right, continuing from the left if necessary, and get to the column from which we start reading/writing our text vertically.

(third encryption, depending on length & time of the cipher, sort of a caesar shift)

– depending on cipher length and column/row pattern chosen, the encryptor crosses out the rest of the checkerboard (as it is not in use). The encryptor then counts the 23 columns to the right and starts writing out the message vertically, adding it to the header and transmitting it, eg in groups of five letters, via morse..

– But, of course, you can still encrypt your message BEFORE encrypting it with Rasterschablone 44 (or have received it in such form). You then can integrate a so-called KENNGRUPPE (Key group into the header to inform about the encryption, eg ’04:17 78 bjc zx km’

– DECRYPTION is likewise (and very simple, btw: using the one time pad to get the key ‘ab cd’ from ‘zx km’, cross-summing the column from where to begin, entering the code text vertically, reading it out horizontally.

Brilliant encryption method, combines SHAPE (GRILLE), ENCRYPTED KEY and CROSS-SUM all simultaneously. Also integrates MONOALPHABETIC WITH ONE TIME PAD (city names) as well as CAESAR (row shift) and TRANSPOSITION (key) while still remaining open to also transmit encrypted messages and it’s keys (Kenngruppe). Highly professional three step encryption with plenty good thoughts to avoid eg city name or number ‘attacks’. Method reminds me modern QR code even.

And: Made in Germany (but invented in Austria – Fleißner Schablone).