Rasterschlüssel 44 (abbr. RS 44) was a manual

cipher In cryptography, a cipher (or cypher) is an algorithm for performing encryption or decryption—a series of well-defined steps that can be followed as a procedure. An alternative, less common term is ''encipherment''. To encipher or encode i ...

system, used by the German

Wehrmacht The ''Wehrmacht'' (, ) were the unified armed forces of Nazi Germany from 1935 to 1945. It consisted of the German Army (1935–1945), ''Heer'' (army), the ''Kriegsmarine'' (navy) and the ''Luftwaffe'' (air force). The designation "''Wehrmac ...

during the

Second World War World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...

. The cipher was designed by the

astronomer An astronomer is a scientist in the field of astronomy who focuses on a specific question or field outside the scope of Earth. Astronomers observe astronomical objects, such as stars, planets, natural satellite, moons, comets and galaxy, galax ...

and sometime

cryptographer Cryptography, or cryptology (from "hidden, secret"; and ''graphein'', "to write", or '' -logia'', "study", respectively), is the practice and study of techniques for secure communication in the presence of adversarial behavior. More gen ...

Walter Fricke while working as a conscript in Section IIb, of Group 2 of OKW/Chi and introduced in March 1944 and the Allied forces codebreakers had considerable difficulties in breaking it.

Cryptanalysis Cryptanalysis (from the Greek ''kryptós'', "hidden", and ''analýein'', "to analyze") refers to the process of analyzing information systems in order to understand hidden aspects of the systems. Cryptanalysis is used to breach cryptographic se ...

, if successful, generally required a 40 letter crib (known plaintext) and some two weeks, making the tactical information outdated before it could be exploited. The combination of strength and ease of use made RS 44 an ideal hand cipher.

Design

The cipher is a transposition based grille cipher, consisting of a grid with 25 columns and 24 rows. Each row contains 10 randomly placed white cells (to be filled with text) and 15 black cells. The columns are labeled with shuffled digraphs and numbers and the rows with digraphs. The key sheet also contains two letter substitution alphabets to encode place names, prior to

encryption In Cryptography law, cryptography, encryption (more specifically, Code, encoding) is the process of transforming information in a way that, ideally, only authorized parties can decode. This process converts the original representation of the inf ...

, and a letter conversion alphabet to encode digraphs. The text is written in the grid, starting from a randomly chosen position, row by row, from left to right. The ciphertext is taken column by column, following the numbering of the columns. The first column to be taken is calculated from the minutes of the message time, the letter count of the message text and the randomly chosen column of the start cell. The message key contains the start position of the text in the grid, designated by the column and header digraphs. The digraphs for the message key are encoded with the letter conversion table and then included in the message header. The secret variable start cell and first column ensure a unique transposition for each message, making multiple anagramming very difficult.

References

External links

Rasterschlüssel 44
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Cipher Machines and CryptologyRasterschlüssel 44
archived fro

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Interesting Ciphers
*https://derekbruff.org/blogs/fywscrypto/historical-crypto/rasterschlussel-44-the-stencil-on-steroids/ {{DEFAULTSORT:Rasterschlussel 44 Classical ciphers History of cryptography History of telecommunications in Germany Research and development in Nazi Germany Signals intelligence of World War II