Fish (cryptography)

Fish, sometimes written FISH, was the codename used by the UK Government Code and Cypher School at Bletchley Park for several German teleprinter stream ciphers of World War II. The traffic ran between the German High Command and army group commanders in the field, so its intelligence value was of the highest strategic importance to the Allies. The name arose when Enigma decrypts showed that the Germans called one wireless teleprinter system Sagefisch, meaning sawfish, and the British then applied fish names to the traffic. Tunny was the name for the first non-Morse link and was later used for the Lorenz SZ40 and SZ42 machines and the traffic they enciphered. Sturgeon named traffic from the Siemens and Halske T52 Geheimschreiber, and Thrasher named traffic probably enciphered on the Siemens T43 one-time tape machine. Cryptanalysis of the Lorenz cipher was aided first by the Heath Robinson machine and later by the Colossus computers.