Discriminant Book

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.[1] The Kenngruppenbuch was produced and used by the Kriegsmarine (German War Navy) during World War II as part of the Naval Enigma message encipherment procedure. The Kenngruppenbuch was used in the generation of the Enigma message Key that was transmitted within the message Indicator. 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.[2] After 1st May 1937, the Kriegsmarine had stopped using an Indicating system with arepetition of message key within the indicator, a serious security flaw, which was still being used by the Luftwaffe (German Airforce) and Heer (German Army) at the beginning of 1940, making the Naval Enigma more secure. [3] The introduction of the K Book was designed to avert this serious security flaw.

In 9th May 1941, when a version of the K Book was recovered from U-boat U-110, Joan Clarke, and her compatriots at Hut 8, the section at Bletchley Park tasked with solving German naval (Kriegsmarine) Enigma messages, noticed that German telegraphists were not acting in a random way, which they were supposed to when making up the message Indicator[4]. 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[4]. It was a problem that the Kriegsmarine later corrected with the introduction of new rules, later in 1941[4].

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 trigrams (Kenngruppen), divided into 733 numbered columns of 24 trigrams displayed in random order.[2] The second half consists of the group list (German:Gruppenlist) where the trigrams are sorted in alphabetical order. After each trigam 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.[2] The table pointer (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 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.[2]

Naval Enigma Operation

Naval Enigma used an Indicator 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[5] The Enigma Cipher Keys called Heimische Gewässer (English Codenme:Dolphin), (Plaice), Triton (Shark), Niobe (Narwhal) and Sucker all used the Kenngruppenbuch and bigram tables to build up the Indicator.

References

  1. ↑ Michael Smith (20 January 2011). The Bletchley Park Codebreakers, Appendix III. Biteback Publishing. p. 390. ISBN 978-1-84954-623-2. Retrieved 22 October 2016.
  2. 1 2 3 4 Alan Mathison Turing; B. J. Copeland (9 September 2004). The Essential Turing. Oxford University Press. p. 271. ISBN 978-0-19-825079-1.
  3. ↑ Sebag-Montefiore, Hugh (21 July 2011). Enigma:The Battle For The Code. Victoria Embankment, London: Orion Publishing Group. p. 69. ISBN 978-1-78022-123-6.
  4. 1 2 3 Sebag-Montefiore, Hugh (21 July 2011). Enigma:The Battle For The Code. Victoria Embankment, London: Orion Publishing Group. p. 69. ISBN 978-1-78022-123-6.
  5. ↑ Friedrich L. Bauer (2006). Decrypted Secrets - Methods and Maxims of Cryptology (4 ed.). Berlin: Springer. p. 61. ISBN 3-540-24502-2.

External links

See also

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