Venona was a secret U.S. counterintelligence program that ran from 1943 to 1980, in which American codebreakers decrypted thousands of messages sent by Soviet intelligence to Moscow during and after the Second World War. The decrypted messages — some 3,000 of the approximately 170,000 intercepted — exposed a substantial Soviet espionage operation in the United States, including the identities of the Cambridge Five, Klaus Fuchs, the Rosenbergs, and dozens of other agents. The program was declassified on July 11, 1995. For more on the KGB article; the Rosenberg case that the decrypts reshaped is detailed in the famous-spies article.
The program began in February 1943, when the U.S. Army’s Signal Intelligence Service started work on Soviet diplomatic cable traffic as a precaution. The Soviet cables, it was discovered, were encrypted with a one-time pad system — the gold standard of cryptography, theoretically unbreakable. American codebreakers at Arlington Hall in Virginia were assigned the project, which they codenamed Venona in 1944. In 1945, a junior analyst, Meredith Knox Gardner, made the discovery that made the program possible: the Soviets, who had run out of one-time-pad material in the early 1940s, had reused pages of the pads in 1941 and 1942. The reuse was the crack in the system. By 1946, Gardner and his colleagues were reading Soviet cables in volume.
What Venona revealed
The Venona decrypts contained thousands of personal names, cover names, and references to institutions. The cryptanalysts did not produce a list of names that could be matched to real persons automatically; the work required the slow, painstaking work of correlating a cover name with an agent, a project with an institution, and a location with an event. By the late 1940s, the FBI, working from Venona, had identified a substantial Soviet network inside the United States. The major cases that Venona resolved or illuminated included:
- The Cambridge Five. The decrypts identified Donald Maclean as a Soviet agent under the cover names “Homer” and “Stanley.” Anthony Blunt was identified as “Lyutsifer” (Lucifer). Kim Philby, less clearly, was identified as a Soviet contact (“Sohnchen,” or “sonny”) in Washington. The MI5 investigation, accelerated by Venona, was the basis for the 1951 defection warning to Burgess and Maclean.
- Klaus Fuchs. Venona identified the cover name “Charles” as Fuchs, the Los Alamos physicist. The identification was passed to British intelligence in 1949, leading to Fuchs’s confession in January 1950.
- The Rosenbergs. Venona identified Julius Rosenberg as “Liberal” and “Antenna.” The cover names appeared in cables that discussed a network run from New York City. The decrypts did not, however, show that Julius had passed any specific atomic secret — the evidence that he had done so remained the testimony of David Greenglass and Anatoly Yatskov.
- Alger Hiss. Venona, in a cable dated 1945, identified an agent in the State Department as a contact for a senior source of information. The identification of the agent, codenamed “Ales,” is widely, though not unanimously, taken to confirm Hiss’s role as a Soviet source. The Hiss case, tried in 1949 and 1950, has been reopened by the Venona disclosures but is not fully resolved.
- Theft of nuclear material. Venona revealed that Soviet intelligence had, on at least one occasion, obtained small samples of uranium oxide from the Manhattan Project’s Oak Ridge facility. The samples were analyzed at the Soviet Academy of Sciences in 1942 and 1943, and the analysis confirmed the feasibility of a gun-type weapon. The case is documented in John Earl Haynes and Harvey Klehr’s Spies (2009).
The decision to keep Venona secret
For half a century the program remained classified. The reasons were partly the usual ones (sources and methods) and partly the political costs of disclosure. The Venona decrypts confirmed that American institutions — the State Department, the Manhattan Project, the Treasury, the OSS — had been penetrated on a scale the McCarthy-era investigations had not suggested in detail and that the late-1940s and 1950s prosecutions had only partially addressed. The disclosures would also have embarrassed British intelligence, which had been the recipient of Venona intelligence and had been slow to act on it. The National Security Agency released the decrypted messages in 1995, on the order of the Director of Central Intelligence, John Deutch, after a multi-year review prompted by Aldrich Ames’s 1994 arrest and the resulting reconsideration of what the agency could safely declassify.
The historiographical consequences have been large. The Rosenbergs, the Hiss case — the Cambridge Five have all been re-evaluated in light of Venona. The earlier revisionist literature, particularly the work of Walter Schneir and Miriam Schneir on the Rosenbergs, has been substantially undermined. The historical consensus now treats the Soviet penetration of the wartime and early postwar American government as substantial, the British and American security services as slow to act on the evidence they had, McCarthy-era claims as exaggerated in their specific charges but correct in their general picture.