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Vernam, Mauborgne, and Friedman: The One-Time Pad and the Index of Coincidence

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The New Codebreakers

Part of the book series: Lecture Notes in Computer Science ((LNSC,volume 9100))

Abstract

The conventional narrative for the invention of the AT&T one-time pad was related by David Kahn. Based on the evidence available in the AT&T patent files and from interviews and correspondence, he concluded that Gilbert Vernam came up with the need for randomness, while Joseph Mauborgne realized the need for a non-repeating key. Examination of other documents suggests a different narrative. It is most likely that Vernam came up with the need for non-repetition; Mauborgne, though, apparently contributed materially to the invention of the two-tape variant. Furthermore, there is reason to suspect that he suggested the need for randomness to Vernam. However, neither Mauborgne, Herbert Yardley, nor anyone at AT&T really understood the security advantages of the true one-time tape. Col. Parker Hitt may have; William Friedman definitely did. Finally, we show that Friedman’s attacks on the two-tape variant likely led to his invention of the index of coincidence, arguably the single most important publication in the history of cryptanalysis.

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Notes

  1. 1.

    Betsy Rohaly Smoot suggests that these two keywords might be a reference to Parker Hitt [37]. Hitt was an expert on riflery and had just coauthored a book on it with Thomas Brown [17].

  2. 2.

    There is some ambiguity about the year of the letter. There is a note on it, apparently by Parker, concluding that it was 1942; Friedman’s October 1943 response [21, Friedman to Parker, 12 Oct 1943], which refers to Parker’s letter as being from “a number of months ago”, makes one suspect that 1943 is more likely. However, since it is Parker’s letter and he concluded that it was 1942, I have used that date.

  3. 3.

    A photocopy of the memo is in the AT&T archives [4, Churchill to Mauborgne, 8 Aug 1918].

  4. 4.

    See Sect. 101–103 of Title 35 of the U.S. Code.

  5. 5.

    U.S. Patent 1,310,719, page 3, column 1, line 18.

  6. 6.

    U.S. Patent 1,356,546, page 2, column 1, line 30.

  7. 7.

    This is from Section 30 of the Patent Act of 1870, which was in effect at the time.

  8. 8.

    The two patents were drafted by the same attorney, G.E. Folk.

  9. 9.

    This text is taken from Kahn’s notes. I was unable to locate Ballard’s letter.

  10. 10.

    Yardley accused Friedman of stealing his solution; Friedman strongly disputed this and noted that his manuscript had been finished in September 1917, before Yardley had even tackled the problem.

  11. 11.

    I have not seen the original of this letter. This excerpt is contained in the attachment [21, Extracts from Correspondence Relating to Solution of A.T. and T. Printing Telegraph Cipher, 12 Oct 1943] to a letter from Friedman to Parker [21, Friedman to Parker, 12 Oct 1943]. The attachment also shows the extent of Yardley’s involvement in the evaluation.

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Acknowledgments

My primary thanks must go to David Kahn. He more than suggested this project, he strongly and repeatedly urged it, even though he realized that the conclusions might disagree with what he wrote all these years ago—as indeed they have. Beyond that, his well-organized notes from 50 years ago were extremely useful.

This paper could not have been begun, let alone written, without the aid of AT&T Archivist George Kupczak. His help was invaluable, especially his work in finding the crucial file folder containing not just the cited letters but also the original paper tapes sent to Fabyan in the challenge. My long-time friend and collaborator Bill Cheswick assisted in the research there.

Equally valuable was the assistance of Paul Barron, archivist at the George C. Marshall Foundation Library; he arranged for access to papers from the William Friedman Collection. Kathleen Kain, independent research assistant for the George C. Marshall Foundation, copied those documents for me.

Ben Lee provided useful guidance on patent legalisms. David Lesher assisted in research at the National Archives.

Betsy Rohaly Smoot of the NSA Center for Cryptologic History, an expert on the Parker and Genevieve Hitt, found many useful files and letters on most of the people mentioned here. Rene Stein of the National Cryptologic Museum Library helped me with access to papers from the Dr. David Kahn Collection.

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  1. Columbia University, New York, USA

    Steven M. Bellovin

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  1. Steven M. Bellovin
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Correspondence to Steven M. Bellovin .

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  1. Université du Luxembourg , Luxembourg, Luxembourg

    Peter Y. A. Ryan

  2. Ecole normale supérieure , Paris, France

    David Naccache

  3. Université Catholique de Louvain , Louvain-la-Neuve, Belgium

    Jean-Jacques Quisquater

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Bellovin, S.M. (2016). Vernam, Mauborgne, and Friedman: The One-Time Pad and the Index of Coincidence. In: Ryan, P., Naccache, D., Quisquater, JJ. (eds) The New Codebreakers. Lecture Notes in Computer Science(), vol 9100. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-662-49301-4_4

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  • DOI: https://doi.org/10.1007/978-3-662-49301-4_4

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