The Chaocipher Clearing House

Progress Report #25

Moshe Rubin (

This Progress Report has been quite some time in coming, being the first report since #24 was uploaded in January 2015.  There is a lot of Chaocipher-related material to catch up on.  So with no further ado, let's see what's happened over the past two years.

Here's a brief listing of items:

A few words on the current state of Chaocipher research

This is a good time to take a step back and examine the current state of Chaocipher research, what has been accomplished, what cryptologic challenges remain, and why Chaocipher research is important to the science of cryptanalysis.

When Chaocipher's system was revealed back in June 2010, a whole host of cryptanalytic challenges presented themselves.  These included deducing the key settings given matching plaintext/ciphertext, given in-depth ciphertext messages, and given a single ciphertext message.  Many of these challenges have been solved, while a few others remain to be solved or improved upon.  For an up-to-date listing of Chaocipher problems and where they stand today, see the "Current State of Chaocipher Research" page.

Why is Chaocipher research important?  Why bother analyzing a system that was never used in the real world?  The answer, in my opinion, is that analyzing Chaocipher leads us to methods that can be used for solving other crypto-systems.  As a case in point, George Lasry's solution of Exhibit 6 added invaluable insights to the science of hill-climbing algorithms.  The techniques used can, and should, be applied when cryptanalyzing other crypto-systems.  Although the systems may differ, the techniques used have much in common.  Chaocipher research may hold the key to solving other crypto-systems.

"Cryptanalysis of Chaocipher and solution of Exhibit 6" (Lasry, Rubin, et al) is published in Cryptologia (Volume 40, Number 6, 2016)

In Progress Report #24, Jeff Calof uploaded a paper to TCCH presenting Professor Cipher Deavours and Lou Kruh's unpublished paper of fifty in-depth Chaocipher messages (aka "Exhibit 6").  At the time of Calof's paper the messages had been unsolved.

In January 2015 Moshe Rubin attempted to solve Exhibit 6 using hill-climbing and simulated annealing software techniques.  Failing to solve the messages, he uploaded his findings to the Crypto Forum in the hope that someone would be able to use his results and succeed in solving them.

In February 2015, George Lasry, and prolific cryptanalytic researcher, succeeded in finding the message plaintexts by searching the Gutenberg Project, and then deducing the Chaocipher key used.  Lasry and co-author Moshe Rubin published a paper in Cryptologia, entitled "Cryptanalysis of Chaocipher and solution of Exhibit 6", The paper advances the science of using hill-climbing for solving ciphers in general, and the Chaocipher in particular.

Aaron Toponce's Chaocipher: a demo video, and implemented as card cipher

Aaron Toponce. Director of System Administration for a Utah based ISP named XMission, is also a passionate amateur cryptographer.  One of his passions is implementing cryptographic systems using playing cards (similar to Cryptonomicon).

Chaocipher followers will enjoy two videos he's uploaded to YouTube:

Twitter has a #chaocipher hashtag

Chaocipher enthusiasts can now enjoy the Twitter #chaocipher hashtag for keeping in touch with each other.  Truth be told, I intend to notify others of Chaocipher news (like this page when it is completed!) through this hashtag.

Scrabble Encryption: A new cipher based on Chaocipher

PR Gomez, a blogger on security issues, invented a cipher he calls "Scrabble Cipher" in 2016.  The cipher is heavily based on Chaocipher but, according to his claims, is simpler than, and is as strong as, the original Chaocipher.  Quoting him:

“This is a cipher based directly on John F. Byrne's Chaocipher from 1918, which was kept secret for many years and finally revealed in 2010. It extends Chaocipher so that the alphabet letter to be moved to the nadir position can be varied rather than always use the same. It also applies a transposition after the main encryption process in order to defeat a known plaintext attack. There are, therefore, three keys plus two numerical values in the 0-25 range, for a total key space of size 26!^3*26^2 = 4.4E82, equivalent to 275 binary bits. The name is because it can be most easily implemented using Scrabble tiles placed on either side of a ruler.”

Check out his interesting blogs:

StackExchange Thread Entitled "Is Chaocipher a secure cipher under ciphertext-only attack?"

There is a StackExchange thread entitled "Is Chaocipher a secure cipher under ciphertext-only attack?".  The question asked is: “While a known plaintext attack successfully finds the keys, nobody has been able to put forward a general solution to this cipher. Is that possible?”.  The answerers include Jeff Calof, a well-respected Chaocipher researcher mentioned above.

Solving a Single Chaocipher Ciphertext Message: One of the Top 10 Open Problems (George Lasry)

In a lecture given by George Lasry at the University of Kassel in Germany on 5 May 2016, Lasry listed his pick of the top ten open problems related to historical cipher systems.  Solving a single ciphertext Chaocipher message is included as #10.

"A Representation of Chaocipher" by Ashley Ray (Master Thesis)

Here is a master thesis entitled "A Representation of Chaocipher" by Ashley Ray(2012)  at the Texas Tech University.  It is an interesting attempt to reduce Chaocipher's encryption method to mathematical terms as a sequence of group theoretical permutations. Chaocipher is a web site aimed at challenging programmers to implement particular coding problems.  The 6 July 2010 post presents Chaocipher and challenges the readers to implement the cipher in the programming language of their choice.  The responses include languages like Haskell, Java, and Scheme (in ten lines!),

An Article about John Francis Byrne in the Irish Times

The Irish Times (Fri, Jan 20, 2017) carried an article entitled “Number Seven’s Son – An Irishman’s Diary about the cryptographer and friend of Joyce, John Francis Byrne”.

New Android application “Cryptography” by Nitramite: Implements Chaocipher

An Android application entitled "Cryptography" and written by a Finnish developer, collects within the application a large number of sub-programs implementing cryptolographic and encryption-related systems.  Examples include ciphers (e.g., Scytale, Rot 1 - 25, Vigenere, Chaocipher, Playfair, Blowfish, Shamir's Secret Sharing (SSS) algorithm), hashes (e.g., HMAC - SHA1 / SHA256 / SHA512, MD-2/4/5, BCrypt), encodings (e.g., Morse code, Braille, ASL (American Sign Language) , and much more.

As mentioned, one of the ciphers implemented is Chaocipher:

Screen capture of Cryptography Android app

Wall Part web site offers Chaocipher posters

The Wall Part web site offers posters made up of Byrne’s original “Chaocipher - The Ultimate Elusion”.  Costing $5.59 apiece, the seven (7) posters are taken from the FOIA (Freedom of Information Act) response published on the Chaocipher Clearing House (TCCH) web site.  Rest assured that TCCH is not connected to Wall Part in any way whatsoever.  Nonetheless, it is amusing to see how Chaocipher is slowly entering the art market!

Online Chaocipher encoder/decoders

There are several online Chaocipher encoders/decoders currently on the web:

Copyright (c) 2012-2017 Moshe Rubin
Created:10 March 2017
Last Updated: 12 March 2017

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