Operation Venona

‘Venona’ was a US counter-intelligence project started in World War II by the US Army’s Signal Intelligence Service (1 February 1943/1 October 1980).

‘Venona’ was created for the decryption of signals transmitted by Soviet intelligence and security agencies such as the NKVD, KGB and GRU. Initiated while the USSR was an ally of the US and UK, the programme continued during the Cold War, when the USSR was seen as an opponent.

During the 37-year duration of the ‘Venona’ programme, the Signal Intelligence Service decrypted and translated about 3,000 signals, and the intelligence yield included discovery of the Cambridge Five espionage ring in the UK and Soviet espionage of the Manhattan Project in the USA. The ‘Venona’ programme remained secret for more than 15 years after its end, and some of the decoded Soviet signals were not declassified and published by the USA until 1995.

During World War II and the early years of the Cold War, the ‘Venona’ programme was a source of information on Soviet intelligence-gathering directed at the Western military powers. Although unknown to the public, and even to Presidents Franklin D. Roosevelt and Harry S Truman, these programmes were of importance concerning crucial events early in the Cold War. These included the Julius and Ethel Rosenberg spying case, and the defections of Donald Maclean and Guy Burgess to the USSR.

Most decipherable signals were transmitted and intercepted between 1942 and 1945. At some time in 1945, the existence of the ‘Venona’ programme was revealed to the USSR by cryptologist and analyst Bill Weisband, an NKVD agent in the US Army’s signals intelligence department. These messages were slowly and gradually decrypted from 1946, and this effort continued (many times at a low level of effort in the latter years) to 1980, when the ‘Venona’ programme was brought to an end and its analytical effort transferred to more important projects.

The ‘Venona’ programme was launched on 1 February 1943 by Gene Grabeel, a US mathematician and cryptanalyst, under orders from Colonel Carter W. Clarke, who was at that time the Chief of the Special Branch of the Military Intelligence Service. Clarke distrusted Iosif Stalin, the Soviet dictator, and feared that the USSR would come to a separate peace with Germany, thereby allowing Germany to focus its military forces against the UK and USA. Cryptanalysts of the US Army’s Signal Intelligence Service analysed encrypted high-level Soviet diplomatic intelligence messages intercepted in large quantities during and immediately after World War II by US, British and Australian listening posts.

This signals traffic, which was encrypted with a one-time pad system, was stored and analysed in relative secrecy by hundreds of cryptanalysts over a 40-year period starting in the early 1940s. When used correctly, the one-time pad encryption system, which has been employed for all the most secret military and diplomatic communication since the 1930s, is unbreakable but, as a result of a Soviet blunder, some of this traffic was vulnerable to cryptanalysis. The Soviet organisation which manufactured the one-time pads produced some 35,000 pages of duplicate key numbers as a result of pressures brought about by the German advance on Moscow late in 1941. The duplication, which seriously undermines the security of any one-time system, was discovered, and attempts to lessen its impact were made by sending the duplicates to widely separated users. Despite this, the reuse was detected by cryptanalysts in the USA.

The Soviet systems in general used a code to convert words and letters into numbers, to which additive keys (from one-time pads) were added, encrypting the content. When used correctly so that the plain text is of a length equal to or less than that of a random key, one-time pad encryption is unbreakable. However, cryptanalysis by US codebreakers revealed that some of the one-time pad material had incorrectly been reused by the Soviets, and thus made possible decryption (sometimes only partial) of a small part of the traffic.

Generating the one-time pads was a slow and labour-intensive process, and the outbreak of war with Germany in June 1941 caused a sudden increase in the need for coded messages. It is probable that the Soviet code generators started duplicating cipher pages in order to keep up with demand.

It was at Arlington Hall that Lieutenant Richard Hallock, working on Soviet ‘Trade’ traffic (so called because these messages dealt with Soviet trade issues), who first discovered that the Soviets were reusing pages. Hallock and his colleagues, among whom were Genevieve Feinstein, Cecil Phillips, Frank Lewis, Frank Wanat, and Lucille Campbell, went on to break into a significant amount of ‘Trade’ traffic, recovering many one-time pad additive key tables in the process.

Meredith Gardner then used this material to break into what was found to be NKVD (and later GRU) traffic by reconstructing the code used to convert text to numbers. Gardner credits Marie Meyer, a linguist with the Signal Intelligence Service, with making some of the initial recoveries of the ‘Venona’ codebook, and Samuel Chew and Cecil Phillips also made valuable contributions. On 20 December 1946, Gardner made the first break into the code, revealing the existence of Soviet espionage in the Manhattan Project. ‘Venona’ codebreaking also indicated that Soviet spies were working in Washington in the Department of State, Treasury, Office of Strategic Services, and even the White House. Very slowly, using assorted techniques ranging from traffic analysis to defector information, more of the messages were decrypted.

One significant aid in the early stages may have been co-operative work undertaken by Japanese and Finnish cryptanalytical organisations, When the Americans broke into Japanese codes during World War II, they gained access to this information. The Finnish radio intelligence service sold much of its material on Soviet codes, including a partially burned code book to the Office of Strategic Services in 1944 within ‘Stella Polaris’.