Lorenz Cipher

Lorenz Cipher

The Lorenz SZ40, SZ42A and SZ42B (SZ for Schlüsselzusatz, meaning "cipher attachment") were German rotor stream cipher machines used by the German Army during World War II. They were developed by C. Lorenz AG in Berlin. They implemented a Vernam stream cipher. British cryptographers, who referred to encrypted German teleprinter traffic as Fish, dubbed the machine and its traffic Tunny.

The SZ machines were in-line attachments to standard Lorenz teleprinters. 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 German High Command in Berlin, and Army Commands throughout occupied Europe. The more advanced SZ42A came in to routine use in February 1943 and the SZ42B in June 1944.

Wireless telegraphy (WT) rather than land-line circuits was used for this traffic. These non-Morse (NoMo) messages were picked up by Britain's Y-stations at Knockholt and Denmark Hill and sent to Government Code and Cypher School at Bletchley Park (BP). Some were deciphered using hand methods before the process was partially automated, first with Robinson machines and then with the Colossus computers. The deciphered messages made an important contribution to Ultra military intelligence.

Read more about Lorenz Cipher:  The Vernam Cipher, Structure, Operation, Cryptanalysis

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