David Kahn
He wrote the book the NSA didn't want published — and then wrote six more.
David Kahn
David Kahn was a Jewish-American journalist and historian from New York who spent fifteen years researching and writing the first comprehensive history of cryptography from antiquity to the twentieth century. The Codebreakers (1967) ran to 1,164 pages and covered every significant cipher, cryptanalyst, and intelligence episode Kahn could document. Its pre-publication manuscript was reviewed by the NSA's predecessor, which reportedly asked Macmillan to delay publication on national-security grounds; the publisher declined. The book became a standard reference, sparked a generation of academic and amateur cryptographers, and effectively created the field of cryptohistory.
Why This Person Matters
Kahn's significance is cultural, historiographic, and indirect-technical. By documenting the complete history of cryptography in one accessible volume, he provided both the historical framework and the motivation for the academic explosion in cryptographic research that characterized the 1970s. Martin Hellman cited The Codebreakers as an influence; Whitfield Diffie read it in college. The cryptographic revolution of the 1970s — public-key cryptography, DES, academic cryptanalysis — had many causes, but the existence of a widely read, rigorously researched history of the field that showed both its depth and its unsolved problems was among them. Kahn spent his lifetime ensuring that the field's history was not forgotten.
The Codebreakers (Macmillan, 1967; revised 1996) traces cryptography from ancient Egypt through the NSA era. Its coverage of WWII cryptanalysis — written before Bletchley Park was declassified — relied on fragmentary public sources and interviews with veterans who could say little. The 1996 revision incorporated three decades of post-declassification scholarship. As a reference work it remains comprehensive and accurate; as historical writing it is also engaging narrative. Kahn researched primary sources in German military archives, interviewed veterans across Europe, and consulted mathematical papers in multiple languages.
The NSA (or its precursor) reviewed the Codebreakers manuscript pre-publication and reportedly raised concerns about several sections. Kahn and Macmillan declined to make substantive changes. The book was published without modification. In subsequent decades, Kahn maintained a civil but wary relationship with US intelligence agencies; he was inducted into the NSA Cryptologic Hall of Honor in 2009, suggesting the institutional tension had dissolved. The episode remains a landmark in the conflict between national security classification and press freedom in the US.
Kahn's subsequent books include: Hitler's Spies (1978), a comprehensive study of German military intelligence in WWII; Kahn on Codes (1983), a general-audience introduction; Seizing the Enigma (1991), a detailed account of US and British naval captures of Enigma material; and The Reader of Gentlemen's Mail (2004), a biography of Herbert Yardley. He died in December 2023 at age 93, having seen virtually every major cryptological secret he had tried to document eventually declassified and confirmed.
| Born | February 7, 1930, Mineola, New York |
| Died | December 28, 2023, Great Neck, New York |
| Education | Bucknell; Oxford (Magdalen); NYU (PhD) |
| Major Work | The Codebreakers (1967, 1996 revised) |
| NSA response | Attempted classified review to delay/suppress publication |
| Later works | The Codebreakers, Hitler's Spies, Seizing the Enigma, The Reader of Gentlemen's Mail |
| Legacy | Defined cryptohistory as a field; inducted NSA Cryptologic Hall of Honor 2009 |