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Cryptanalysis of Typex

2014; Taylor & Francis; Volume: 38; Issue: 2 Linguagem: Inglês

10.1080/01611194.2013.797051

1558-1586

Kelly C. Chang, Richard M. Low, Mark Stamp,

Chaos-based Image/Signal Encryption

Abstract Abstract 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 an enormous impact on the war. However, despite being based on the commercial version of the Enigma, there is no documented successful attack on Typex during its time in service. This article covers the Typex machine. Researchers consider the development of Typex, discuss how Typex works, and present and analyze two 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. The second attack assumes that the rotor wirings are unknown. This ciphertext-only attack uses a hill-climb to determine the wirings of the stepping rotors. Finally, researchers briefly consider an attack developed by Polish cryptanalysts to recover the Enigma rotor wirings, and they argue that Typex was significantly more resistant to this particular attack. Keywords: cryptanalysisEnigmahill climbrotor machineTypex Acknowledgment The authors thank an anonymous referee for providing several fascinating and relevant references to the archival literature. Additional informationNotes on contributorsKelly ChangKelly Chang works as a software engineer in the Silicon Valley. She remains interested in cryptology and looks forward to continuing her research on Typex.Richard M. LowRichard M. Low, PhD, is a Lecturer in the Department of Mathematics at San Jose State University. His research interests include combinatorics, group theory and cryptology.Mark StampMark Stamp can neither confirm nor deny that he spent seven years as a National Security Agency cryptanalyst. However, he can confirm that for the past 11 years, he has been Professor of Computer Science at San Jose State University (SJSU). At SJSU, Dr. Stamp teaches courses in information security and supervises many Master's student projects. He has published numerous research articles in security and he never fails to mention his textbooks, Information Security: Principles and Practice, 2nd edition, Wiley 2011, and Applied Cryptanalysis: Breaking Ciphers in the Real World, Wiley-IEEE Press 2007 (the latter co-authored with Richard M. Low).