In 1995 the National Security Agency (NSA) released details of the Venona Project, a top secret U.S. military intelligence program to decipher Soviet cablegrams that had begun in 1943 and was formally closed in 1980.
For some historians (e.g., Haynes and Klehr), the information contained in these messages about Soviet spies in the United States offers conclusive proof that McCarthy-era fears about Communist infiltration of the U.S. government—often dismissed as bordering on the paranoid—were quite accurate after all.
Other historians, however, question the reliability of the decryptions as a “smoking gun” because of the incomplete and tentative nature of the deciphering, and therefore dispute the conclusion that the red scare of the 1940s and 1950s was justified.
Hearing rumors of a secret German–Soviet peace deal, in February 1943 Colonel Carter Clarke of the U.S. Army’s Special Branch instructed the Signal Intelligence Service (forerunner of the NSA) to attempt to decode Soviet diplomatic cable traffic to and from its embassies and consulates passing through the United States.
The two-stage cipher system used by the Soviet Union was in theory unbreakable, but, by a mixture of skill, perseverance, and luck (the accidental duplication by the Soviet manufacturer of the “one-time pads” used in the encipherment produced a recurrent flaw), the army code-breakers managed to render the first of 2,900 intercepted messages sent between 1940 and 1948 partially readable by 1946—by which time the war was over. However, the messages turned out to reveal not secret peace-deal negotiations but evidence that the Soviet Union had been organizing an espionage campaign against the United States since 1942.
The deciphered cables indicated that the Soviet Union had recruited informants in most U.S. government and military agencies at all levels, and they mentioned several hundred U.S. citizens or resident aliens (almost always by code name) who were involved with the Soviet Union in some capacity.
The task of deciphering the original messages continued slowly, on and off, until 1980. During the McCarthy years, the FBI and CIA used the Venona decryptions to identify new spies, to corroborate existing information gained from prominent Communist defectors like Elizabeth Bentley and Whittaker Chambers, and to confirm the guilt of atomic spies such as Klaus Fuchs and Julius Rosenberg.
It is arguable, however, that the method of deciphering the messages meant that their revelations were potentially circular: the cryptographers sometimes used as a working hypothesis an identification of the real person behind the code name that had been fed to them by other intelligence agencies, which then in turn used the partially decrypted messages as confirmation of their suspicions about a particular individual. In many cases, the association of a code name with a particular individual remains speculative or unknown.
Nevertheless, in combination with the partial opening up of the Soviet archives after 1991, the Venona cables offer the possibility of significant new interpretations of the emergence of the cold war, placing it much earlier than commonly thought.
The project remained secret until 1995, as U.S. intelligence agencies insisted that it was more important not to reveal how successful it had been in cracking Soviet codes. There was also a recognition that the cables would be ruled as hearsay and hence inadmissible as evidence in a court of law, so their release would not have been of immediate use.
Some commentators (Moynihan) have argued recently that this continuing secrecy was a mistake, as the Venona Project would have clarified a lot of the muddied water about Communist infiltration during the cold war, allowing the American people to have a clearer picture of the extent of Soviet espionage based on fact rather than rumor and paranoia.
While the Venona documents would have been taken to confirm, for example, that Julius Rosenberg was indeed guilty of passing on atomic secrets, they would also have demonstrated that Dean Acheson (secretary of state in the Truman administration) was not the Communist conspirator that Senator Joseph McCarthy accused him of being.