Kahn's first published book, The Codebreakers - The Story of Secret Writing (1967), has been widely considered to be a definitive account of the history of cryptography.

It was during this period that he wrote an article for the New York Times Magazine about two defectors from the National Security Agency.

Most of the editing, German translating, and insider contributions were from American World War II cryptographer Bradford Hardie III.

William Crowell, the former deputy director of the National Security Agency, was quoted in Newsday as saying "Before he (Kahn) came along, the best you could do was buy an explanatory book that usually was too technical and terribly dull.

[8] A committee of the United States Intelligence Board concluded that the book was "a possibly valuable support to foreign COMSEC [communications security] authorities" and recommended "further low-key actions as possible, but short of legal action, to discourage Mr. Kahn or his prospective publishers.

Kahn continued his work as a reporter and op-ed editor for Newsday until 1998 and served as a journalism professor at New York University.

He also lived in Washington, D.C.; Paris, France; Freiburg, Germany; Oxford, England; and Great Neck, New York.