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Original Articles

John F. Byrne's Chaocipher Revealed: An Historical and Technical Appraisal

Pages 328-379
Published online: 20 Oct 2011
 
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Abstract

Chaocipher is a method of encryption invented by John F. Byrne in 1918, who tried unsuccessfully to interest the US Signal Corp and Navy in his system. In 1953, Byrne presented Chaocipher-encrypted messages as a challenge in his autobiography Silent Years. Although numerous students of cryptanalysis attempted to solve the challenge messages over the years, none succeeded. For 90 years, the Chaocipher algorithm was a closely guarded secret known only to a handful of persons. Following fruitful negotiations with the Byrne family during the period 2009–2010, the Chaocipher papers and materials have been donated to the National Cryptologic Museum in Ft. Meade, MD. This paper presents a comprehensive historical and technical evaluation of John F. Byrne and his Chaocipher system.

Acknowledgments

This author would like to acknowledge and thank the following people who were instrumental and helpful in the writing of this article: Tony Bean (John Byrne's nephew) for generously sharing genealogical information about the Byrne family and for proof-reading from a unique vantage point; David Kahn for inspiring my life-long interest in cryptanalysis in general and Chaocipher in particular, and for facilitating the successful connection to the National Cryptographic Museum (NCM); David D'Auria for negotiating the donating of the Chaocipher material with Pat Byrne; Jeff Hill for the hundreds of absorbing Chaocipher-related hours and emails traded with this author, and for proofreading this paper; Jeff Calof for providing the highest level of proofreading of this and other Chaocipher papers written by this author, and for valuable leads and ideas; Mike Cowan for coming aboard and contributing to the ongoing attack on Chaocipher; and my wife Rochelle, for her excellent proofreading of this paper and constant support.

This author has a special debt to repay to three women without whose help this paper, and the story of Chaocipher, could not have been written: Pat Byrne, for magnanimously heeding the call of history and donating her father-in-law's entire collection of Chaocipher-related artifacts to NCM. Chaocipher researchers and historians will owe her a debt for generations to come. Cheryl Needle who, as Pat Byrne's associate in parallel with her own illustrious career as a book antiquarian, was highly instrumental in making the Chaocipher donation to NCM a reality. Rene Stein, NCM Librarian, who responded to every request I had from NCM with exactly the material I needed, providing it promptly, efficiently, and always with a smile.

Special thanks are due to the National Cryptologic Museum of the NSA, Ft. Meade, MD, USA, for permission to reproduce pictures and photographs from the Chaocipher archives currently residing in the library.

Thanks are also due to the Curran Collection for permission to reproduce photographs of John F. Byrne. The Curran Collection—Photographs. Reproduced with kind permission of Helen Curran Solterer, from the originals held in UCD Library Special Collections. Digital image is a copyright of UCD Irish Virtual Research Library and Archive.

Additional information

Notes on contributors

Moshe Rubin

Moshe Rubin is a software engineer residing in Jerusalem, Israel. He received his B.Sc. in Computer Science from the Jerusalem College of Technology in 1979. His interest in cryptanalysis began at age fifteen after reading David Kahn's The Codebreakers from cover to cover multiple times, and it was Kahn's description of Chaocipher that led to a life-long fascination with this cipher.
 

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