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 ''Heer'' (army), the ''Kriegsmarine'' (navy) and the ''Luftwaffe'' (air force). The designation "''Wehrmacht''" replaced the previou ...
during the
Second World War
World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the World War II by country, vast majority of the world's countries—including all of the great power ...
.
The cipher was designed by the
astronomer
An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, planets, moons, comets and galaxies – in either o ...
and sometime
cryptographer
Cryptography, or cryptology (from grc, , translit=kryptós "hidden, secret"; and ''graphein'', "to write", or '' -logia'', "study", respectively), is the practice and study of techniques for secure communication in the presence of adv ...
Walter Fricke
Walter Ernst Fricke (1April 191521March 1988) was a distinguished German professor of theoretical astronomy at the University of Heidelberg. He was a mathematician and cryptanalyst during World War II at the Wehrmacht signals intelligence agen ...
while working as a conscript in Section IIb, of Group 2 of
OKW/Chi and introduced in March 1944 and the
Allied forces codebreakers
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 sec ...
had considerable difficulties in breaking it.
, 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crib (known plaintext) and some two weeks, making the tactical information outdated before it could be exploited.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, encryption is the process of encoding information. This process converts the original representation of the information, known as plaintext, into an alternative form known as ciphertext. Ideally, only authorized parties can dec ...
, 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 44o
Cipher Machines and CryptologyRasterschlüssel 44
archived fro
o
Interesting Ciphers
{{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