As a logical continuation of Jeff Calof's trip to the National Cryptologic Museum (NCM), it turns out he uncovered papers describing how Cipher Deavours and Lou Kruh enciphered their Chaocipher challenge as published in the July 1990 issue of Cryptologia ("Chaocipher enters the computer age when its method is disclosed to Cryptologia editors"). Jeff submitted a paper to Cryptologia entitled "Chaocipher Exhibit 5: History, Analysis, and Solution of Cryptologia's 1990 Challenge", scheduled for publication in the January 2014 issue of Cryptologia.
Without encroaching on the upcoming article, suffice it to say that Deavours and Kruh used the classic Chaocipher algorithm to encipher but selected very complicated keying parameters, rendering their three messages piteously inadequate material for anyone to solve. The paper describes the entire encryption process and discusses questions about the challenge messages, errors in the messages, and their fairness.
You can read the paper's abstract on The Chaocipher Clearing House.
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