Chaocipher Exhibit 5: History, Analysis, and Solution of Cryptologia's 1990 Challenge
Chaocipher is a method of encryption invented by John F. Byrne in 1918. For over 40 years, he unsuccessfully tried to interest various U.S. Government agencies and private industries in his cipher system. His 1953 biography included a series of challenge ciphers he labeled Exhibits 1-4. In 1990, John Byrne (son of John F. Byrne) revealed and demonstrated the Chaocipher algorithm to Professor Cipher Deavours and Louis Kruh. Without revealing the encipherment process, they in turn published an article including a new series of challenge ciphers they called Exhibit 5. Twenty-three years later, and three years after the first public revelation of the Chaocipher algorithm, Exhibit 5 remained unsolved. Following a 2013 visit to the National Cryptologic Museum (NCM) in Ft. Meade, Maryland to research the recently donated Byrne family materials on the Chaocipher, co-author Jeff Calof found two documents prepared by Deavours and Kruh pertaining to Exhibit 5. One document provides their encipherment schema and solution for the published version, while the other is for an earlier draft whose challenge ciphers differ markedly from that of the published article. This article presents a review of Exhibit 5's creation, an analysis of the restrictions placed on Deavours and Kruh when writing their article, their enciphering schema and source material for the published Exhibit 5, irregularities with the published ciphertext, and an overview and comparison with their unpublished Exhibit 5 draft and challenge ciphers.
chaocipher exhibit 5 cryptologia byrne john byrne cipher deavours louis kruh david kahn greg mellen john f silent years stewart c easton the codebreakers william f friedman william sutton