The Discriminant Book (German: ''Kenngruppenbuch''; literally: ''Groups to identify the key to the receiver'') shortened to K-Book (''K. Buch''), and also known as the ''indicator group book'' or ''identification group book'' was a secret distribution list in booklet form, which listed trigraphs in random order. The Kenngruppenbuch was introduced in May 1937, and used by the

Kriegsmarine The (, ) was the navy of Germany from 1935 to 1945. It superseded the Imperial German Navy of the German Empire (1871–1918) and the inter-war (1919–1935) of the Weimar Republic. The was one of three official branches, along with the a ...

(German War Navy) during

World War II 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 vast majority of the world's countries—including all of the great powers—forming two opposin ...

as part of the Naval Enigma message encipherment procedure, to ensure secret and confidential communication between

Karl Dönitz Karl Dönitz (sometimes spelled Doenitz; ; 16 September 1891 24 December 1980) was a German admiral who briefly succeeded Adolf Hitler as head of state in May 1945, holding the position until the dissolution of the Flensburg Government follo ...

, Commander of Submarines (BdU) in the

Atlantic The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe an ...

and in the

Mediterranean The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on the e ...

operating German submarines. The Kenngruppenbuch was used in the generation of the

Enigma Enigma may refer to: *Riddle, someone or something that is mysterious or puzzling Biology *ENIGMA, a class of gene in the LIM domain Computing and technology * Enigma (company), a New York-based data-technology startup * Enigma machine, a family ...

message Key that was transmitted within the message

Indicator Indicator may refer to: Biology * Environmental indicator of environmental health (pressures, conditions and responses) * Ecological indicator of ecosystem health (ecological processes) * Health indicator, which is used to describe the health o ...

. The Kenngruppenbuch was used from 5 October 1941, for the Enigma Model M3, and from 1 February 1942 exclusively for the Enigma M4. It must not be confused with the Kenngruppenheft which was used with the Short Signal Book (German: ''Kurzsignalbuch'').

History

The Kenngruppenbuch was a large document with the first edition coming into force in 1938, that mostly remained unchanged when a second edition was released in 1941. The Zuteilungsliste, however, was continually updated. After 1 May 1937, the Kriegsmarine had stopped using an Indicating system with a repetition of message key within the indicator, a serious security flaw, which was still being used by the

Luftwaffe The ''Luftwaffe'' () was the aerial-warfare branch of the German ''Wehrmacht'' before and during World War II. Germany's military air arms during World War I, the ''Luftstreitkräfte'' of the Imperial Army and the '' Marine-Fliegerabtei ...

(German Airforce) and Heer (German Army) at the beginning of 1940, making the Naval Enigma more secure. The introduction of the K Book was designed to avert this serious security flaw. On 9 May 1941, when a version of the K Book was recovered from U-boat U-110,

Joan Clarke Joan Elisabeth Lowther Murray, MBE (''née'' Clarke; 24 June 1917 – 4 September 1996) was an English cryptanalyst and numismatist best known for her work as a code-breaker at Bletchley Park during the Second World War. Although she did not ...

, and her compatriots at

Hut 8 Hut 8 was a section in the Government Code and Cypher School (GC&CS) at Bletchley Park (the British World War II codebreaking station, located in Buckinghamshire) tasked with solving German naval (Kriegsmarine) Enigma messages. The section was l ...

, the section at

Bletchley Park Bletchley Park is an English country house and estate in Bletchley, Milton Keynes ( Buckinghamshire) that became the principal centre of Allied code-breaking during the Second World War. The mansion was constructed during the years following ...

tasked with solving German naval (Kriegsmarine) Enigma messages, noticed that German

telegraphist A telegraphist (British English), telegrapher (American English), or telegraph operator is an operator who uses a telegraph key to send and receive the Morse code in order to communicate by land lines or radio. During the Great War the Royal ...

s were not acting in a random way, which they were supposed to when making up the message Indicator. Rather than selecting a random trigram out of the K Book, the telegraphist had a tendency to choose a trigram from either the top of the column list, or near the bottom and grouped in the middle. It was a problem that the Kriegsmarine later corrected with the introduction of new rules, later in 1941.

Design

The Kenngruppenbuch consisted of two main parts. The first half consisted of the Column List (German:Spaltenliste) which consisted of all 17,576 of

trigram Trigrams are a special case of the ''n''-gram, where ''n'' is 3. They are often used in natural language processing for performing statistical analysis of texts and in cryptography for control and use of ciphers and codes. Frequency Context is ...

s (Kenngruppen), divided into 733 numbered columns of 24 trigrams displayed in random order. The second half consists of the group list (German:Gruppenlist) where the trigrams are sorted in alphabetical order. After each trigram are 2 numbers, the first giving the number of the column in the Spaltenliste in which the trigram occurs, the second giving the position of the trigram in the column. The table pointer, or table selection chart (German:Tauschtafelplan) told the operator which column of a given table was used to select the required trigrams. By means of the Assignation list (German:Zuteilungsliste) told the radio man which table he should use for a particular cipher net. Large keys would be given several blocks of columns, small keys as few as 10. Tauschtafelplan Bruno from set Quelle

Naval Enigma Operation

Naval Enigma used an

to define a key mechanism, with the key being transmitted along with the ciphertext. The starting position for the rotors was transmitted just before the ciphertext, usually after having been enciphered by Naval Enigma. The exact method used was termed the indicator procedure. A properly self-reciprocal bipartite digraphic encryption algorithm was used for the super-encipherment of the indicators (German:Spruchschlüssel) with basic wheel settings The Enigma Cipher Keys called ''Heimische Gewässer'' (English Codename: Dolphin), (Plaice), ''Triton'' (Shark), ''Niobe'' (Narwhal) and Sucker all used the Kenngruppenbuch and

bigram A bigram or digram is a sequence of two adjacent elements from a string of tokens, which are typically letters, syllables, or words. A bigram is an ''n''-gram for ''n''=2. The frequency distribution of every bigram in a string is commonly used f ...

tables to build up the Indicator. The Indicator was built up as follows: Two Trigrams were chosen at random. The first trigraph was taken from the Key Identification Group table (German:Schlüsselkenngruppe), from the Kenngruppenbuch as determined in the Zuteilungsliste. The second trigraph was taken from the encryption indicator group or Process characteristic groups table (German:Verfahrenkenngrupp),also taken from the Kenngruppenbuch and also determined in the Zuteilungsliste. For example: S W Q - and R A F, and arranged in the scheme: ∗ S W Q
R A F ∗ with the empty position would be filled in a random letter: X S W Q
R A F P Encipherment with a

Bigram A bigram or digram is a sequence of two adjacent elements from a string of tokens, which are typically letters, syllables, or words. A bigram is an ''n''-gram for ''n''=2. The frequency distribution of every bigram in a string is commonly used f ...

table called double-letter conversion table (German:Doppelbuchstabentauschtafel), arranged with vertical pairs, was as follow: X→V S→G W→V Q→X
R→I A→F F→T P→T which would give V G V X
I F T T This was read out vertically, giving: VIGF VTXT and this was sent without further encoding, and preceding the encrypted message. The message was sent by

Morse Morse may refer to: People * Morse (surname) * Morse Goodman (1917-1993), Anglican Bishop of Calgary, Canada * Morse Robb (1902–1992), Canadian inventor and entrepreneur Geography Antarctica * Cape Morse, Wilkes Land * Mount Morse, Churchi ...

and on the receiving end the procedure was reversed. Nine bigram tables were known to exist, including FLUSS or FLUSZ (English:River)). Other bigram booklets existed and were used including BACH (1940), STROM (1941) and TEICH, UFER etc.

History

Design

Naval Enigma Operation

See also

References

Further reading