Fish (cryptography)

: " For the (Fibonacci Shrinking) stream cipher published in 1993, see FISH (cipher)."

Fish (sometimes FISH) was the Allied codename for any of several German teleprinter stream ciphers used during World War II [Wolfgang W. Mache, "Geheimschreiber" ("Cryptology: Yesterday, Today and Tomorrow", Artech House, Norwood, 1987)] [Cipher A. Deavours and Louis Kruh, "Mechanics of the German Telecipher Machine" (also reprinted in "Cryptology: Yesterday, Today and Tomorrow")] [Wolfgang W. Mache, "The Siemens Cipher Teletype in the History of Telecommunications" (reprinted in "Selections from Cryptologia: History, People, and Technology", Artech House, Norwood, 1998)] . Enciphered teleprinter traffic was used between German High Command and Army Group commanders in the field, so its intelligence value (Ultra) was of the highest strategic value to the Allies. [ Copeland (2006) p. 47 ] This traffic normally passed over landlines, but as German forces extended their reach out of western Europe, they had to resort to wireless transmission. [ Citation | last = Lewin | first = Ronald | publication-date = 2001 | year = 1978 | title = Ultra Goes to War: The Secret Story | series = Classic Military History | publication-place = Harmondsworth, England | publisher = Penguin Books | page = 130 ]

In June 1941, the "Y" wireless intercept stations, as well as receiving Enigma-enciphered Morse code traffic, started to receive non-Morse traffic which was initially called NoMo. [ Copeland (2006) p. 338 ] NoMo1 was an experimental german army link between Berlin and Athens, and NoMo2 an airforece link between Berlin and Königsberg. The parallel Enigma-enciphered link to NoMo2, which was being read by Bletchley Park, revealed that the Germans called the wireless teleprinter transmission systems "Saegefisch" (sawfish), so the name "Fish" was adopted for this traffic. [ Gannon (2006) p. 102 ] The enciphering/ deciphering equipment was called a "Geheimschreiber" (secret writer) which, like Enigma, used a symmetrical substitution alphabet. The teleprinter code used was Murray's modification of the 5-bit Baudot code. The NoMo1 link was named Tunny, a name which later went on to be used both for the Lorenz SZ40/42 "Geheimschreiber" machines, and also for the Bletchley Park analogues of them.

A large number of links were monitored by the Y-station at Knockholt and given names of fish. These included Bream (Berlin-Rome), Herring (Rome-Tunis), Jellyfish (Berlin-Paris), Grilse (Berlin-La Roche), Mullet (Berlin-Oslo), Turbot (Berlin-Copenhagen), Dace (Berlin-Königsberg), Whiting (Königsberg-Riga), Perch (Königsberg-Central Belarusse), Squid (Königsberg-N Ukraine), Octopus (Königsberg-E Ukraine), Stickleback (Königsberg-S Ukraine), Smelt (E Ukraine-S Ukraine), Grayling (Königsberg-Belgrade), Tarpon (Berlin-Bucharest), Gurnard (Berlin-Belgrade), Chubb (Belgrade-Salonica), Flounder (Salonika-Rhodes) and Codfish (Berlin-Salonika). [ Copeland (2006) p. 41 ]

Sturgeon was the name given to traffic encoded with the Siemens and Halske T52 "Geheimschreiber". [ Citation | last = Weierud | first = Frode | title = Blechley Park's Sturgeon — The Fish That Laid No Eggs in Copeland (2006) pp. 307-327 ] In May 1940, after the German invasion of Norway, a Swedish mathematician and cryptographer Arne Beurling used intercepted traffic from telegraph lines that passed through Sweden, to break this cipher. [ Citation | last = McKay | first = Craig | title = German Teleprinter Traffic and Swedish Wartime Intelligence in Copeland (2006) pp. 328-333 ] Although Bletchley Park eventually dignosed and broke Sturgeon, the relatively low value of the intelligence gained, compared to the effort involved, meant that they did not read much of its traffic.

Thrasher was the name used for traffic enciphered on a "Geheimschreiber" that was probably the Siemens T43 one-time tape machine. This was used only on a few circuits, in the later stages of the war and was diagnosed at Bletchley Park, but considered to be unbreakable.

List of senior executives and cryptographers on FISH

* Ralph Tester linguist and head of Testery
* Max Newman mathematician and head of Newmanry
* Jerry Roberts shift-leader, linguist and senior codebreaker
* Peter Ericsson shift-leader, linguist and senior codebreaker
* Victor Masters shift-leader and senior codebreaker
* Denis Oswald linguist and senior codebreaker
* I J (Jack) Good statistician and codebreaker
* Donald Michie codebreaker
* Peter Hilton codebreaker
* Peter Benenson codebreaker
* Peter Edgerle codebreaker
* John Christie codebreaker
* John Thompson codebreaker
* Roy Jenkins codebreaker
* Henry Whitehead mathematician and codebreaker
* Shaun Wylie mathematician and codebreaker
* Tom Colvill general Manager

Notes

References

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