Editing Lorenz cipher (section)

{{Short description|Cipher machines used by the German Army during World War II}}
{{Use dmy dates|cs1-dates=ly|date=June 2015}}
[[File:Lorenz-SZ42-2.jpg|300px|right|upright=1.35|thumbnail|The Lorenz SZ42 machine with its covers removed. [[Bletchley Park]] museum]]
The '''Lorenz SZ40''', '''SZ42a''' and '''SZ42b''' were German [[Rotor machine|rotor]] [[stream cipher]] machines used by the [[German Army (Wehrmacht)|German Army]] during [[World War II]].  They were developed by [[C. Lorenz AG]] in [[Berlin]]. The model name ''SZ'' is derived from ''Schlüssel-Zusatz'', meaning ''cipher attachment''. The instruments implemented a [[Gilbert Vernam#The Vernam cipher|Vernam]] [[stream cipher]].

British [[cryptanalyst]]s, who referred to encrypted German [[Electrical telegraph|teleprinter]] traffic as [[Fish (cryptography)|''Fish'']], dubbed the machine and its traffic '''''Tunny''''' (meaning tunafish) and deduced its logical structure three years before they saw such a machine.<ref>{{Harvnb|Hinsley|1993|p=141}}</ref>

The SZ machines were in-line attachments to standard [[teleprinter]]s. An experimental link using SZ40 machines was started in June 1941. The enhanced SZ42 machines were brought into substantial use from mid-1942 onwards for high-level communications between the [[Oberkommando der Wehrmacht|German High Command]] in [[Wünsdorf]] close to Berlin, and Army Commands throughout occupied Europe.<ref>{{Harvnb|Hinsley|1993|p=142}}</ref> The more advanced SZ42A came into routine use in February 1943 and the SZ42B in June 1944.{{sfn|Copeland|2006|pp=38, 39|loc="The German Tunny Machine"}}

[[Radioteletype]] (RTTY) rather than land-line circuits was used for this traffic.<ref name = "GRoT11A4" >{{Harvnb|Good|Michie|Timms|1945|p=4}} of ''German Tunny''</ref> These [[Frequency-shift keying#Audio frequency-shift keying|audio frequency shift keying]] non-[[Morse code|Morse]] (NoMo) messages were picked up by Britain's [[Y-stations]] at [[Knockholt]] in Kent, its outstation at [[Higher Wincombe]]<ref name="Kenworthy">{{cite web|url=https://discovery.nationalarchives.gov.uk/details/r/C11205560|title=The National Archives: The interception of German Teleprinter Communications at Foreign Office Station Knockholt - Piece details HW 50/79|access-date=2023-12-15}}</ref> in Wiltshire, and at [[Denmark Hill]] in south London, and forwarded to the [[Government Communications Headquarters#Government Code and Cypher School|Government Code and Cypher School]] at [[Bletchley Park]] (BP). Some were deciphered using hand methods before the process was partially automated, first with [[Heath Robinson (codebreaking machine)|Robinson machines]] and then with the [[Colossus computer]]s.<ref>{{Harvnb|Good|1993|pp=160–165}}</ref> The deciphered Lorenz messages made one of the most significant contributions to British ''[[Ultra (cryptography)|Ultra]]'' [[military intelligence]] and to [[Allies of World War II|Allied]] victory in Europe, due to the high-level strategic nature of the information that was gained from Lorenz decrypts.<ref>{{Cite web|url=https://cs.stanford.edu/people/eroberts/courses/soco/projects/colossus/history.html|title=The History of the Lorenz Cipher and the Colossus Machine|website=Stanford University|access-date=9 September 2018}}</ref>