David Kahn, whose 1967 book, “The Codebreakers,” established him as the world’s pre-eminent authority on cryptology — the science of making and breaking secret codes — died on Jan. 24 in the Bronx. He was 93.
His son Michael said the death, at a senior living facility, was from the long-term effects of a stroke in 2015.
Before Mr. Kahn’s book, cryptology itself was something of a secret. Despite an explosion in cryptological technology and techniques during the 20th century and the central role they played in World War II, the subject was typically overlooked by historians, if only because their possible sources were still highly classified.
“Codebreaking is the most important form of secret intelligence in the world today,” Mr. Kahn wrote in his book’s preface. “Yet it has never had a chronicler.”
Over the course of more than 1,000 pages, along with some 150 pages of notes, Mr. Kahn laid out cryptology’s long history, starting with ancient Egypt 4,000 years ago and proceeding through the French and American revolutions, and the innovations wrought by the advent of the telegraph and telephone to the mid-20th century and the dawn of computer-assisted code breaking.
The U.S. government considered the book so volatile that the National Security Agency, the country’s premier cryptology arm, pondered how to block its publication. It even considered breaking into Mr. Kahn’s home in Great Neck, N.Y.
Eventually the agency chose more overt means, demanding that the publisher, Macmillan, not release it. The company refused; instead, Macmillan and Mr. Kahn submitted the text to the Department of Defense for review. Mr. Kahn agreed to cut a few paragraphs about Britain’s code-breaking efforts during World War II, which were still classified, but otherwise he kept the book intact.
Despite its heft and subject matter that was then arcane, “The Codebreakers” was a hit. It sold about 75,000 hardcover copies, landed Mr. Kahn an appearance on “The Tonight Show” and introduced countless readers to the subject.
It also inspired a growing community of private-sector cryptologists who, until then, had been stymied by the federal authorities. Until the late 1960s, anyone who submitted a patent for a cryptological device or technique would receive a visit from an agent; the government would even go so far as to hire such inventors — simply to gain control of their intellectual property.
“There was so little available about cryptography,” Steven Levy, the author of “Crypto: How the Code Rebels Beat the Government Saving Privacy in the Digital Age” (2001), said in an interview. “And when you got past the books for kids about using a wheel, decoder rings and things like that, the serious work was classified.”
But as Mr. Kahn argued, in his book and elsewhere, cryptology needed to be free; the coming digital communications revolution and the need to keep such communications secure demanded it. By providing a detailed map of where cryptology had been, he motivated aspiring coders to push further — Mr. Kahn’s book, Mr. Levy said, was “their bible.”
David Kahn was born on Feb. 7, 1930, in Manhattan and grew up in Great Neck, on the North Shore of Long Island. His mother, Florence (Abraham) Kahn, owned a glassmaking factory, and his father, Jesse Kahn, was a trial lawyer.
A chance encounter sparked David’s interest in codes. When he was a teenager, he spied a book in the Great Neck public library: “Secret and Urgent” (1939), by Fletcher Pratt, a history of secret codes filled with the sort of cloak-and-dagger intrigue that makes a heart race.
“It hooked me — and I never grew up,” he told The Washington Post in 1978.
Mr. Kahn received a bachelor’s degree in social science from Bucknell University in 1951, then went to work for Newsday, on Long Island, as a reporter.
Cryptology remained a side interest until 1960, when he wrote an article for The New York Times Magazine on the subject’s history, inspired by the defection of two employees of the National Security Agency to the Soviet Union. The employees took a trove of U.S. code-breaking secrets with them.
The story piqued public interest in the N.S.A. and won Mr. Kahn the book contract that resulted in “The Codebreakers.” He left Newsday to write it, after which he moved to a job as a copy editor with The International Herald Tribune in Paris.
His marriage to Susanne Fiedler in 1969 ended in divorce in 1994. Along with his son Michael, he is survived by another son, Oliver.
While in Europe, Mr. Kahn pursued a doctorate in modern German history at Oxford, where he studied under the eminent English historian Hugh Trevor-Roper.
His dissertation, titled “Hitler’s Spies: German Military Intelligence in World War II,” was published as a book in 1978.
The book, which drew in part on extensive interviews with former high-ranking Nazi officials, demonstrated that Germany’s intelligence apparatus had been woefully behind those of Britain and the United States, and as a result had led the country to commit strategic blunders — including the failure to foresee the Allied invasion of Italy and the assumption that the D-Day landings were a diversion.
Mr. Kahn later returned to Newsday as a copy editor, but he kept writing about codes. In addition to several more books, he founded the first academic journal on the subject, Cryptologia, which he also edited.
In a curious twist, in 1993, the N.S.A. invited Mr. Kahn to be its scholar in residence. Despite the agency’s earlier efforts to sideline his work, by the 1990s it had come to respect him for advancing the field of cryptology. In 2020, he was even named to its hall of fame.
“A journalist, scholar and author with a career spanning more than half a century,” the agency said, “Dr. David Kahn has done more than any single individual to educate the public, around the world, about the importance of cryptology to international peace and security.”