The Chaocipher Clearing House

Moshe Rubin (

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Welcome to my Chaocipher-related web page, dedicated to solving John Francis Byrne's cryptographic invention he called "Chaocipher".  Unsolved for so many years, it finally took 57 years (from the publication of Byrne's "Silent Years" in 1953 until June 2010) for the cipher algorithm to be revealed.

Here you'll find ongoing information about Chaocipher research carried out to date.  In addition, this website carries historical facts and items pertaining to John F. Byrne, and through him, about James Joyce and other friends of Byrne's.

Although the basic Chaocipher algorithm is known today, there remains much that needs to be solved.  It is my hope that this web page will stimulate someone to solve and investigate other Chaocipher-related cryptanalytic challenges.  See this page for the current state of Chaocipher research, including open problems and challenges.

Please view this site as a community/global effort.  I will gladly upload any information anyone may have regarding Chaocipher.  Please address all e-mails to


Here are basic materials to get you started.

Ongoing Research and Updates

Date Title Comment
February 19, 2009 Progress report #1 Summary of my work to date
February 25, 2009 Progress report #2 Proposing a new hypothetical system closer to Chaocipher's characteristics
March 3, 2009 Progress report #3 Evidence that Chaocipher incorporates a blocking of 13- or 26-letters
March 6, 2009 Link to Chaocipher-related blogs on Nick Pelling's Cipher Mysteries blog site
March 6, 2009 Progress Report #4 (a) Summarizing my current hypothesis, (b) examining Exhibit #4 for its settings.
Updated 11 March 2009 with comment from Jeffrey Hill.
March 13, 2009 Progress Report #5 Searching for the plaintexts to Deavours's and Kruh's challenge messages ("Chaocipher Exhibit 5")
March 20, 2009 Progress Report #6 Repetitions in the exhibits, index of coincidence measurements on the first 100 lines in Exhibit 1, references in  the open literature with relevance to Chaocipher, a misunderstanding in the relationship between Byrne and William F. Friedman, trying to place Exhibit 5 Message 3.
April 3, 2009 Progress Report #7 Comments from readers; distributions; experimenting with cipher disks; thoughts about the Chaocipher mechanism; the Wheatstone cryptograph; alphabet cycle decomposition
April 7, 2009 Progress Report #8 Jeff Hill's paper entitled "A Feasible Mechanism for the 1918 Byrne Cryptograph", presented at the American Cryptogram Association's 1990 convention in Montreal.
April 16, 2009 Progress Report #9 Jeff Hill's excellent internal paper entitled "Chaocipher: Analysis and Models", revised in 2009.
April 16, 2009 Progress Report #10 NSA's reply to a Freedom of Information Act request to declassify Chaocipher-related information
April 22, 2009 Progress Report #11 Correspondences relating to Jeff Hill's Paper "Chaocipher: Analysis and Models" (Jeff Hill, Mike Cowan, and Moshe Rubin)
June 2, 2009 New on-line Chaocipher-related discussion group now hosted on The Crypto Forum.
June 5, 2009 Thanks to Jeff Hill for pointing out an error in the on-line Exhibit 1 ciphertext file (line 119 group 11 needed to be changed from "BBDCD" to "BKDCD").
June 9, 2009 Once again, kudos to Jeff Hill for pointing out several typos in the TCCH copies of Exhibits 1-4 -- thanks, Jeff!  Here's a link to a text file listing all of Jeff's corrections.
July 13, 2009 Progress Report #12 William F. Friedman's historical document "Preliminary Historical Report of the Solution  of the "B" Machine" and the surprising parallels between PURPLE and Chaocipher.
July 28, 2009 Progress Report #13 Mike Cowan's paper entitled "A new approach to revealing the Byrne machine".  In this paper Mike Cowan presents a plan of action for attacking the Chaocipher based on the plethora of plain and cipher text letters.
October 1, 2009 Historical Correspondences Related to Chaocipher.  A comprehensive listing of all available letters between John F. Byrne and William F. Friedman related to Chaocipher.  Also includes letters to and from other persons.
October 24, 2009 Added a "What's New" page to track all additions and changes to the TCCH web site.
October 30, 2009 Progress Report #14 No Chaocipher material at GCHQ; Jeff Hill submits research paper entitled "A Feasible Mechanism for the 1937 Byrne Cryptograph"; An important consideration for the (1,1,2,4) Hidden Markov Model steppings; FOIA reply from NSA was a "Granted in Full" disposition
March 29, 2010 Progress Report #15 Mike Cowan submits a new paper entitled "An appraisal of the present enciphering models for Chaocipher".
June 1, 2010 Progress Report #16 The National Cryptologic Museum Foundation (NCMF) acquires the Chaocipher machine and papers, system soon to be revealed.
July 2, 2010 Progress Report #17 Chaocipher revealed: the actual algorithm is described publicly for the first time.
August 8, 2010 Progress Report #18 Deciphering Exhibit #1: An in-depth analysis of Exhibit #1 in Byrne's "Silent Years"
November 19, 2010 Progress Report #19 Jeff Calof submits a new paper entitled "'Silent Years' - Chapter 21 (Chaocipher) Examined: Analyzing Byrne’s Assertions".
December 18, 2010 Progress Report #20 Mike Cowan submits a new paper: "Chaocipher: Solving Exhibits 1 and 4"
April 27, 2012 Progress Report #21 Chaocipher paper "John F. Byrne's Chaocipher Revealed: An Historical and Technical Appraisal" published in Cryptologia, Patricia Byrne passes away at 92
October 5, 2013 Progress Report #22 Jeff Calof, with co-authors Jeff Hill and Moshe Rubin, publish "Chaocipher Exhibit 5: History, Analysis, and Solution of Cryptologia's 1990 Challenge" in Cryptologia (Volume 38, Number 1, 2014).  Esa Peuha submits a new paper: ""Deciphering Chaocipher Exhibits 2 & 3"
March 22, 2014 Progress Report #23 Jeff Calof submits a short paper describing the solution to Kruh and Deavours's Exhibit #5 messages
January 9, 2015 Progress Report #24 Jeff Calof and Moshe Rubin submit the paper "Chaocipher: Exhibit 6", a real-life challenge by Lou Kruh and Cipher Deavours
October 30, 2015 Link to PDF Rear Admiral (ret.) P. D. Tucker was present at Byrne's Chaocipher presentation in Washington D.C. on 3 May 1938.  In a letter to David Kahn following publication of "The Codebreakers", Tucker gives a first-person description of what transpired at the meeting.
March 11, 2017 Progress Report #25 Catch-up on Chaocipher-related research over the past two years.  A table showing up-to-date information on Chaocipher research and open challenges.
November 4, 2018 Link to PDF Added a PDF file containing a section from Henry E. Langen's personal memoirs "Cryptography - Confidential" describing in detail all of Langen's Chaocipher-related meetings with John F. Byrne.  See the web page "Historical Correspondences Related to Chaocipher" (3 November 1954) for the historical context.
February 16, 2019 Progress Report #26 Belated obituaries for Mike Cowan and Jeff Hill, George Lasry's "A Methodology for the Cryptanalysis of Classical Ciphers with Search Metaheuristics", revisiting the Chaocipher characteristic "no hits < 9", Chaocipher II 8086 assembly code program listings, Chaocipher Sightings on the Web.
August 4, 2020 Progress Report #27 Chaocipher mentioned in Craig P. Bauer's book "Unsolved!"; Ken Hannigan's paper on John F. Byrne and his connection to Wicklow, Ireland; "Roaming Zenith": an alternate way of displaying permuted Chaocipher alphabets; Chaocipher hypothesis re "no hits < 7" is finally proven; An off-the-wall attempt to link between Chaocipher and the Zodiac ciphers; Musings regarding Chaocipher research, and more.
January 12, 2023 Progress Report #28 Two-years catchup here resulting in a larger-than-usual delight of topics: ICCH video presentation "The Hunt for Chaocipher"; Photos of John F. Byrne's places of residence; Introductory letter sent to Patricia Byrne after locating her; CrypTool2 supports Chaocipher; Ken Hannigan's biographical paper on John F. Byrne; and much more ...

Copyright (c) 2009-2020 Moshe Rubin, All Rights Reserved.
Created: 19 February 2009
Last Updated:6 February 2023