The Chaocipher Clearing House

Progress Report #10

Moshe Rubin (

Results of a Freedom of Information Act (FOIA) Request for Chaocipher Information

On 21 March 2009 I filled out a Web-based form to NSA/CSS requesting declassified information about Chaocipher under the Freedom of Information Act (FOIA):

[. . .]

Six months ago I initiated research into John F. Byrne's "Chaocipher" machine device, launching a web site dedicated to this fascinating historical cipher.  My site can be found at  Information about the history of the Chaocipher machine device, as well as Chaocipher references in the open literature, can be found on that site.

The open literature refers numerous times to the fact that John F. Byrne met, and was in postal contact, with Major Frank Moorman and William F. Friedman in 1922 regarding the "Chaocipher" device.  At the time, William F. Friedman was employed as a civilian cryptanalyst at the Military Intelligence Division, War Department, Office of the  Chief of Staff, Washington.

Apparently, Byrne was very keen on interesting the military in adopting his device.  Like many other claims by inventors regarding its indecipherability, the device was probably unsuited for practical usage.  John F. Byrne's Chaocipher device was never adopted by any cryptologic agency, much to Byrne's chagrin and frustration.  In 1953 he published a book, entitled Silent Years, in which he presented a long Chaocipher cipher challenge to the cryptologic community at large.  His challenge was never solved.

I would like to ask if NSA:

(a) Has any information about Byrne's meetings with officials like Moorman, Friedman, etc. in 1922 or at any other time regarding his "Chaocipher" device
(b) Has any technical information about the Chaocipher device and its analysis
(c) Would be willing to declassify any information about the Chaocipher device that may reside in its records

Thanking you in advance,

Moshe Rubin

The NSA site clearly states that it is difficult to estimate the amount pf processing time needed due to many factors.  To be honest, I was ready for a long wait until I would hear back from them.

Therefore, I was surprised to receive an envelope from NSA in the mail three weeks later.  The package, mailed on 2 April, contained a cover letter and eleven photocopied pages.

Here are some comments:
It is inconceivable that NSA has no other files relating to Chaocipher it is willing to divulge.  Although Byrne never provided William F. Friedman with the required fifty messages for analysis, I am convinced that Friedman or one of his students analyzed the system throughly to convince themselves that the system did not pose a threat to American communications security.  It is curious that this is all NSA is willing to declassify.  It is hoped that the non-governmental cryptologic community will solve the Chaocipher without needing input from NSA and similar organizations.

Copyright (c) 2009 Moshe Rubin
Created: 16 April 2009
Updated: 12 November 2018

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