THE VENONA INTERCEPTS
Washington, D.C. (1946-1980)
Events: Postscript -- The Nuclear Age, 1945-present

Soviet intelligence officers in the United States regularly communicated with their superiors in Moscow via telegraphic cables.  These messages were encrypted of course, but in 1946 the United States, with the assistance of Great Britain, began to decrypt a good number of these messages.  This program led to the eventual capture of several Soviet spies within the Manhattan Project.  The VENONA intercepts, as they were codenamed, remained a closely-guarded secret, known only to a handful of government officials, until the program was declassified in 1995.  

The cables should have been impossible to decrypt.  Collecting them was easy.  The United States government simply acquired copies of all cables openly sent to and from various Soviet embassies and consulates.  These messages were encrypted by a means known as a "one-time pad."  This meant that, at least in theory, decrypting them should have been impossible.  The Army's Signal Intelligence Service began working on the problem in 1943, and they gradually discovered a Soviet procedural error that allowed many of the messages to be painstakingly decrypted.  Portions of messages began to become clear in 1946, and by 1948 numerous messages were being recovered by the team led by Meredith Gardner (above).  In 1948, the Federal Bureau of Investigation (FBI) was also brought into the investigation, its efforts led by Robert Lamphere (right).  Although only messages up to 1945 were vulnerable to decryption, and these messages were several years old by that point, they still contained references to spies who had never been detected, including many who presumably continued to work for Soviet intelligence.  From 1948 to 1951, numerous Soviet spies were uncovered and prosecuted this way, including the atomic spies Klaus Fuchs (below), David Greenglass, Greenglass's handler Julius Rosenberg, and Rosenberg's wife Ethel.  Other sources, such as Theodore Hall, were detected, but without sufficient corroborating evidence other than VENONA, the government was unable to prosecute them.  (The VENONA secret was considered too valuable to reveal as evidence in an open court proceeding.)  

Once messages were decrypted and translated into English, however, the identity of the individuals mentioned in them was still often not apparent.  Soviet intelligence assigned every person a unique codename and sometimes changed it.  (For example, Julius Rosenberg was ANTENNA, later changed to LIBERAL, and Theodore Hall was MLAD.)  Nonetheless, it was often possible to determine who each codename referred to based on clues within the messages.  Sometimes the message where the individual is first given a codename happens to be one of those decrypted, in which case the individual's identity is known with certainty.  In other cases, rather obvious clues make identification simple, such as when the name of ANTENNA's wife was openly given as "Ethel."  Most people were identified through follow-up investigation by the FBI based on the descriptions of their work, their lives, their appearance, and even their codename itself.  (MLAD means "youngster" in Russian; Hall was only 19 when he began his work as a spy.)  In some cases, especially when dealing with sources who were only mentioned in a handful of decrypted messages, a Soviet spy's identity remains unknown to this day.  

Additional wartime messages continued to be decrypted during the 1950s and beyond, but the "value added" of these decryptions gradually lessened over time.  Soviet intelligence learned of the VENONA program in 1949 through its highly-placed British agent, Kim Philby, but there was nothing they could do to stop it.  The program was finally formally terminated on October 1, 1980.  

Rumors of an important codebreaking effort circulated among journalists and historians throughout the 1980s and the early 1990s, but there was no formal confirmation of the existence of VENONA until it was declassified in 1995.  Today anyone who is interested can view images of the actual decrypted cables on the National Security Agency's web page at http://www.nsa.gov/venona/index.cfm.