The Friedman's report about Hebern 5 rotors machine

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Introduction

W. Friedman, in 1934, published a report entitled "ANALYSIS OF A MECHANICO-ELECTRICAL CRYPTOGRAPH, PART I", which summarizes all the work he accomplished on Mr Hebern's cipher machine equipped with 5 rotors, in particular he describes the methods he used to succeed in the challenge which the Navy launch to him in 1924. This report was intended for the internal use of the Army signal service. It remained classified for decades (50, 60, 90 years?) [1].

This report is a completely essential text in the history of cryptology in the same way as Rejewski's report concerning the analysis of the Enigma or Turing's professor's book. Indeed it reveals in detail the methods used by W. Friedman to break Hebern's encryption machine. If we place ourselves in the context of the 1920s, this is the very first work of cryptanalysis which shows that a complex encryption machine can be broken and more over via manual methods. Friedman's work is simply extraordinary. If only one proof were needed, the fact that his report remained classified for so long proves it. Friedman deserves for his work on Hebern's machine (not counting the rest), to be included in the top 5 of the greatest cryptanalysts in history.

[1] Note: What is certain is that this report was reclassified CONFIDENTIAL in 1983 (see NSA ID:A2919767 & ID:A2919743). On the other hand, in 2015, the NSA declassified the second part of the report, concerning an evolution of the machine broken in 1924 by Friedman. In short, I could not find the exact date of declassification of this report. Perhaps it is still classified 100 years after the Navy challenge?

The heart of the report: the interval method

The heart of the report concerns the methods Friedman used in 1924 to win the challenge thrown at him by the Navy (link).

In all the methods that Friedman used, there are mainly the use of a statistical method which allowed us to reconstruct the wiring of the rotor in position V (the fast rotor or right rotor). This step is essential, because then, more or less easily, a cryptologist is able to reconstruct the plain text of the messages.

This method, which I call "Interval method" (Friedman does not give it a name) is a very original statistical method. I think this is the main reason his report remained classified for so long because it may be applicable to other issues.

The plan of the work

SECRET

Register N°XX

WAR DEPARTMENT
Office of the Chief Signal Officer
Washington

ANALYSYS of a MECHANICO-ELECTRICAL
CRYPTOGRAPH

Part I

Technical Paper by William Friedman, Cryptanalyst, Chief of Signal Intelligence Section, War Plans of Training Division

UNITED STATES, Goverment Printing Office, Washington: 1934

CONTENTS

  • Section I. Introductory remarks
  • Section II. Description of machine and its operation
  • Section III. Basic cryptographic principles of operation
  • Section IV. Analysis based only upon a knowledge of the mechanics of the machine
  • Section V. The table of basic cipher-text sequences
  • Section VI. Mathematical theory of analysis
  • Section VII. Reconstruction of table of basic cipher-text sequences
  • Section VIII. General observations
  • Section XI. Reconstruction of Alphabet 5
  • Section X. Practical application of principles
  • Section XI. Further steps in analysis
  • Section XII. Solution without preliminary analysis of any line of text
  • Section XIII. Reconstruction of other alphabets
  • Section XIV. Reverse encipherment
  • Section XV. Miscellaneous
  • Appendix

Some topics studied in detail

In other pages concerning the Hebern machine and its cryptographic study, I described some of the methods discovered by Friedman. Here is, Below is a reference to these pages:

  • Find the rotor wiring in position V
    This is the page where I describe the interval method. This topic is covered in sections IV to X of the report. (link).
  • Find the plain text of a few lines of the cryptogram
    This topic is covered in section X of the report, paragraph 53. (link).
  • Find the rotor wiring in position I.
    This topic is covered in section XI, paragraphs 54 and 55 of the report. (link).
  • Find the wiring of pseudo-rotor S equivalent to rotors II, III, IV. Find the plain text of the cryptograms (after steps 3 and/or 4)
    This topic is covered in section XI, paragraph 56 of the report. (link).
  • Find the wiring of the rotors in position II, III and IV.
    This topic is covered in section XIII of the report. (link).
  • Is knowledge of RFS wiring necessary?
    This topic is covered in section VIII. (link)
  • Reverse encipherment (link).
  • Find the wiring of the rotors when the plain text is known.
    This topic is covered in section XV, paragraph 85. (link)
Note: I remind you that I did not use Friedman's notation, nor the same examples as him. On the other hand, I tried to simplify the understanding of his methods.

Web Links

  • ANALYSIS OF A MECHANICO-ELECTRICAL CRYPTOGRAPH, PART I, TECHNICAL PAPER, BY WILLIAM F. FRIEDMAN Cryptanalyst, Chief of Signal Intelligence Section UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1934, Secret. (link)
  • NSA - Friedman collection - classification of the report about Hebern cipher machine - 1983 - REF. ID:A2919767
  • NSA - Friedman collection - comparison between the report by Friedman and the book by Deavours & Kruh - 1983 - REF. ID:A2919743. Note: The conclusion of this document is to retain the report of Friedman classified.
  • NSA - Friedman collection - The Legendary William F. Friedman, By Lambros D. Callimahos, 12 pages, Unclassified, ID: A4045961. 1974. ( link).