The Chaocipher Clearing House

Current State of Chaocipher Research

Moshe Rubin (

This page represents the most up-to-date summary of  Chaocipher research.  The page lists Chaocipher cryptologic challenges, whether they have been solved, and any other important information.

In the following table, the "Chaocipher System" refers to the "Classic" (i.e., all plaintext letters are located in the right alphabet) or the "Extended" (the plaintext letters are located in either the right or the left alphabets based on a predetermined key) systems.

Problem: Recover key given ... Chaocipher System Current State Research Additional Information
Date Description
Ciphertext and corresponding plaintext Classic Solved 2010 Scheffler
2011 Rubin
2015 Crypto Forum
Ciphertext and corresponding plaintext Extended Open This has not yet been tackled.
In-depth messages, given ciphertext and plaintext Classic Solved
(requires at least 10 messages)
2016 Lasry/Rubin
Extended Solved
(requires at least 20 messages)
2016 Lasry/Rubin
In-depth ciphertext-only messages Classic Solved
(requires 60-80 messages)
2015 Crypto Forum Unsuccessful attempt to solve them using hill-climbing
2016 Lasry/Rubin Successful solution of Exhibit 6.  Can it be solved with fewer messages?
Extended Solved
(requires 600-800 messages)
ditto ditto Successful solution of Exhibit 6.  Can it be solved with fewer messages?
A single ciphertext message Classic Open
Extended Open

Copyright (c) 2012-2017 Moshe Rubin
Created:11 March 2017

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