Cryptanalysis of the SIGABA cipher
Heather Ellie Kwong · 2008
SIGABA is a rotor-based cipher machine that is famous for its service during World War II by the United States.Compared to other ciphers used in World War II, such as the German Enigma or the Japanese Purple, SIGABA's security was undefeatable, as it was the only cipher to withstand all cryptanalytic attacks in the course of its usage.This thesis covers the history of SIGABA's development, how SIGABA works, and a cryptanalytic attack on SIGABA.The attack covered in this thesis has never been implemented before and is divided into a primary phase and secondary phase.The attack recovers SIGABA's keyspace by targeting SIGABA's rotor banks separately, while demonstrating SIGABA's strength in design that separates it from other ciphers.