CRYPTANALYSIS OF THE SIGABA CIPHER

By Heather Kwong

SIGABA is a rotor-based cipher machine that was used during World War II by the United States.  Compared to other comparable cipher machines, such as the German Enigma or the Japanese Purple, SIGABA was far superior, as it was the only WII-era cipher to withstand all cryptanalytic attacks over the course of its service lifetime.

This thesis covers the history of SIGABA's development, how SIGABA works, and a cryptanalytic attack on SIGABA.  The attack covered in this thesis had not been previously implemented.  The attack, which recovers the key by targeting SIGABA's rotor banks separately, clearly demonstrates the strength of the SIGABA design.