William F. Friedman

American cryptologist

Also known as: William Frederick Friedman

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July 23, 2026

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William F. Friedman was an American cryptologist who, along with his wife Elizebeth S. Friedman, played a crucial role in deciphering enemy codes during both World War I and World War II. He studied genetics at Cornell University and later became the chief cryptoanalyst in the Signal Intelligence Service, leading teams that broke various Japanese codes, including the Purple machine cipher. Friedman also authored "The Index of Coincidence and Its Applications in Cryptography". Together, the Friedmans co-authored "The Shakespearean Ciphers Examined".1

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William F. Friedman and Elizebeth S. Friedman
William Friedman was still an infant when his family immigrated to the United States; he studied genetics at Cornell University (B.S., 1914). Elizebeth Smith majored in English at Hillsdale (Michigan) College (B.A., 1915). They met at the Riverbank Laboratories (Geneva, Illinois), where they both eventually…
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William Friedman was still an infant when his family immigrated to the United States; he studied genetics at Cornell University (B.S., 1914). Elizebeth Smith majored in English at Hillsdale (Michigan) College (B.A., 1915). They met at the Riverbank Laboratories (Geneva, Illinois), where they both eventually…
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cryptology
Vernam-Vigenère ciphers
…conclusion drawn by Mauborgne and William F. Friedman that the only type of cryptosystem that is unconditionally secure uses a random onetime key. The proof of this, however, was provided almost 30 years later by another AT&T researcher, Claude Shannon, the father of modern information theory.
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…conclusion drawn by Mauborgne and William F. Friedman that the only type of cryptosystem that is unconditionally secure uses a random onetime key. The proof of this, however, was provided almost 30 years later by another AT&T researcher, Claude Shannon, the father of modern information theory.
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