Rotor cipher machines played a large role in World War II: Germany used Enigma; America created Sigaba; Britain developed Typex. The breaking of Enigma by Polish and (later) British cryptanalysts had a huge impact on the war. Despite be- ing based on the commercial version of the Enigma, there is no documented successful attack on Typex during its time in service. This project covers the Typex machine. We consider the development of Typex, we discuss how Typex works, and we present and analyze two distinct cryptanalytic attacks on the cipher. The first attack assumes the rotor wirings are known and uses Turing’s crib attack–originally developed for Enigma–to recover the settings of the stepping rotors. It then performs a hill-climb to recover the static rotor settings. The second attack assumes that the rotor wirings are unknown. This attack uses a nested hill-climb to find the wirings of the stepping rotors.
Chang, Kelly, "CRYPTANALYSIS OF TYPEX" (2012). Master's Projects. 235.