David Kahn, a journalist and historian who unlocked the hidden world of cryptology in his best-selling 1967 book “The Codebreakers” and became a preeminent scholar of signals intelligence, revered even among the keepers of the secrets he revealed, died Jan. 23 at his home in the Bronx. He was 93.
The cause was complications from a stroke in 2015, according to his family.
Dr. Kahn was 13 and was passing by his local library in Great Neck, N.Y., when he noticed a book called “Secret and Urgent: The Story of Codes and Ciphers” by military historian Fletcher Pratt. The title alone “stopped me in my tracks,” Dr. Kahn told The Washington Post years later.
Fascinated by the intrigue contained in the book’s pages, he became an amateur cryptologist — a person concerned with cryptography, or the making of codes, and cryptanalysis, or the breaking of them — and maintained the interest beyond boyhood into his career as a newspaperman.
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Dr. Kahn was working for Newsday on Long Island in 1960 when two mathematicians employed by the National Security Agency, William H. Martin and Bernon F. Mitchell, defected to the Soviet Union and laid bare the communications-gathering activities of the NSA. Among other charges, they claimed the United States had cracked the codes of 40 other countries, including numerous allies.
Located at Fort Meade, Md., the NSA was and remains so secretive that its acronym has long been joked to stand for “No Such Agency.” Amid the clamor surrounding the defection, Dr. Kahn pitched a freelance magazine story to the New York Times explaining the history of cryptology. The article became the germ of his first and best known book.
“The Codebreakers,” billed as “the first comprehensive history of secret communication from ancient times to the threshold of outer space,” was an immediate sensation.
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In more than 1,000 pages of prose that was both authoritative and readable, and with no security clearance to ease his research, Dr. Kahn carried the reader through thousands of years of history — from the age of cuneiform writing to the Napoleonic era, through the deciphered Zimmermann telegram of World War I and code breaking in World War II to the modern-day activities of the NSA.
“Nobody wrote about this stuff,” said Nicholas Reynolds, the author of “Need to Know: World War II and the Rise of American Intelligence.” “He opened the door to a whole new field, basically, the history of signals intelligence.”
It was a door that many U.S. government officials wished to remain closed. James Bamford, a journalist who has written extensively on American intelligence, described in his 1982 book “The Puzzle Palace: A Report on America’s Most Secret Agency,” the steps the NSA considered taking to block the publication of Dr. Kahn’s work or limit the extent of its disclosures.
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Those measures, ultimately rejected, included “hiring Kahn into the government so that certain criminal statues would apply if the work was published … undertaking ‘clandestine service applications’ against the author, which apparently meant anything from physical surveillance to a black-bag job; and conducting a ‘surreptitious entry’ into Kahn’s Long Island home,” Bamford wrote.
According to Bamford, Macmillan, Dr. Kahn’s publisher, submitted the entire manuscript to the Defense Department, which responded that “it would not be in the national interest to publish the book.” In the end, Macmillan and Dr. Kahn agreed only to delete several paragraphs relating to NSA’s cooperation with British intelligence.
Even when the popularity of Dr. Kahn’s book landed him on NBC’s “Tonight Show,” NSA employees were barred from acknowledging the existence of the volume. But over the years, as Dr. Kahn continued writing well-received books on signals intelligence, and as the NSA’s national security mission became more broadly understood, the two parties reached what was by all accounts a relationship of mutual admiration.
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In the 1990s, William Crowell, then deputy director under NSA director Mike McConnell, pushed for Dr. Kahn to be named a scholar in residence at the agency.
“I could not think of anyone in the entire country who had as much knowledge of cryptography and cryptanalysis in the public sector as he had,” Crowell said. “He proved that there was a lot of information available, and that having a knowledge about it was an important part of looking ahead to the future, when it would become essential to our well-being.”
David Kahn was born in Manhattan on Feb. 7, 1930. His father, a lawyer, and his mother, the owner of a glass factory, raised their three children on Long Island.
While nurturing his budding interest in cryptology, Dr. Kahn crafted word puzzles that were published in comic books in the 1940s. As a teenager, he undertook a correspondence with William F. Friedman, known as the dean of modern American cryptographers, who encouraged his interest in the field.
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Dr. Kahn received a bachelor’s degree in social science in 1951 from Bucknell University in Lewisburg, Pa., where he worked on the student newspaper. Ineligible for military service in Korea because of poor vision, he began his journalism career.
Starting in 1955, he was a reporter for Newsday. He took time off to write “The Codebreakers” before moving overseas to work on what was then the Paris edition of the New York Herald Tribune. (Dr. Kahn later returned to Newsday.)
In 1974, while still in Europe, he received a doctorate in modern history from the University of Oxford in England, where his dissertation became the basis for his book “Hitler’s Spies: German Military Intelligence in World War II” (1978). Dr. Kahn interviewed nearly a dozen high-ranking Nazis for the book.
“I had rather thought that with their efficiency they would have had a number of successes, but it was almost an unrelenting story of failure,” he told The Post of Hitler’s intelligence service. “First, their information was flawed and insufficient, partly because Hitler appointed lesser personnel to intelligence work. But even if he had received perfect intelligence, his arrogance would never have let him believe, say, that the Russians weren’t completely incompetent, inferior and would fall apart once attacked.”
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Dr. Kahn’s later books included “Seizing the Enigma: The Race to Break the German U-boat Codes, 1939-1943” (1991) and “The Reader of Gentlemen’s Mail: Herbert O. Yardley and the Birth of American Codebreaking” (2004).
Dr. Kahn’s marriage to Susanne Fiedler ended in divorce. Survivors include two sons, Oliver Kahn of Florence, Colo., and Michael Kahn of Manhattan.
Two decades ago, Dr. Kahn set out to find a permanent home for his papers and his extensive collection of books and artifacts from the field of intelligence, among them an 1806 letter from Napoleon asking his son to correspond in code, as well as patents for U.S. cipher machines. He chose the NSA’s National Cryptologic Museum.
In a poignant turnabout from his tense early days researching the agency, the museum’s library is now home to the David Kahn Collection.
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For years, the NSA was a “spooky black hole at Ford Meade that no one really talked about,” said Vince Houghton, the museum’s director. “David Kahn was able to write about it and write about it correctly decades before the general public understood it. That was something that no one thought could be done.”
Long ago, Dr. Kahn had a turn as president of the American Cryptogram Association, a group of hobbyists who trade and attempt to break one another’s codes. He was, by his own admission, not a great cryptanalyst. The finest ones, he had observed, tend to be mathematicians and musicians, people attuned to pattern and repetition.
He could work for ages on a book, he once told the New York Sun, but “I’m not one of these guys that can sit for days, weeks, and years solving a code.”
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