Lorenz cipher

The Lorenz cipher was a class of German rotor stream cipher machines used by the German Army during World War II. It was mostly used for messages among headquarters. This machine and its messages were eventually worked out by the team at Bletchley Park during World War II.

The Lorenz SZ42 machine with its covers removed. Bletchley Park museum

British cryptanalysts (codebreakers) worked out its logical structure three years before they saw the machine.^[1][2]