Venona was the cover name given to the activity by US and UK intelligence agencies to exploit the intercepted communications of the Russian spy agencies. The timescale of the intercepts was very narrow covering the period 1941 to 1948. However, what was revealed was to have quite seismic effects on the US and UK establishments.

The Americans realised that the Russians were using the Western Union facilities for sending messages between Moscow and Russian State facilities abroad such as embassies and consulates. Interception was therefore easy. However, the Russians were using an encoding system that should have been unbreakable. They had an extensive code book(s) which contained words and phrases which were represented by groups of numbers. The matter was further secured by using a ‘one-time pad’ system which gave a formula by which the original code could be changed for transmission. It should be a completely secure method of encryption.

On 01 Feb 43, the Americans set up a small team of originally 2 people at their Arlington Hall base of what was then the precursor of the National Security Agency (NSA) to look at this ‘Russian problem’. However, it was quickly realised that this was a vast task and the number of people involved was hugely increased. Analysis of the traffic showed that there were several types of traffic being sent by this method. Messages of both diplomatic and trade channels; NKVD channels; GRU channels. (The NKVD was the state intelligence service and the GRU was the military intelligence service. The NKVD became the KGB in 1954). (NKVD – Narodny Komissariat Vnutreny Del; GRU – Glavnoye Razvedyvatelnoye Upravleniye; KGB – Komitet Gosudarstvennoy Bezopasnosti).

It took many years of dedicated analysis of the messages to find errors and ways of exploiting these errors. It was a laborious process encrypting long passages and coding clerks being human will, when pressed, take short-cuts or use one-time pads more than “one time”. In 1948 the UK’s Government Communications Headquarters (GCHQ) became an active member in the work on the Venona product. They provided much linguistic support and helped build the Russian’s original codebook.

Decryption of Venona traffic was not a real time event, nor was it complete for every message. For example, most of the messages sent from New York to Moscow in 1944 to 1945 were not decrypted until the period 1947 to 1952. The best decryption rate for other periods was around 2%. Even then, not every message was fully translated. There would still be gaps. Additionally, the Russians used codenames for people and places. The intelligence services of the US and UK had carried out covert surveillance of Russian suspect agents. By going back through these reports, it was possible to relate subsequent messages related to activities by those agents and their contacts. (This enabled the footnotes shown in the illustration above to be added to the decrypt).

The outcome of all this effort? The Americans learned that in their Manhattan Project had been someone who had been passing atomic bomb information to the Russians. Julius Rosenberg was discovered to be at the centre of a web of people inside the project providing information to the Russians. Here in the UK, Venona led to the uncovering of the “Cambridge Five” – Philby, Burgess McClean, Cairncross and Blunt. All held senior posts in the either the intelligence services, the Foreign Office or central government. Philby had learned of Venona in 1949 when he was made liaison to the Federal Bureau of Investigation. However, other than warn the others to their discovery as traitors, there was little that could be done as all the decrypts were historical. These two cases were the headlines. There were other minor revelations as to the extent of Russian penetration into US and UK society.

Work on decrypting Venona messages continued until Oct 80. It was believed that by then any people identified would be either too old or dead to be of interest. The degree of penetration by the Russians into the US and UK establishment discovered in the relatively small number of messages gave rise to a degree of ‘state paranoia’. In the vaults of NSA are some 700,000 Venona texts of which only some 2,700 were decrypted, so, if those 2,700 threw up Rosenberg and the Cambridge Five, who is lurking in the remaining 697,300? The tone for the Cold War had been set.