It seems that post war both the Soviet Union and Britain were able to gain access to our secret diplomatic communications. This time however it was thanks to ‘bugs’ and spies rather than cryptanalysis.
One step forward, two steps back…
Let’s take a look at the relevant information:
From ‘The Mitrokhin Archive-The KGB in Europe and the West’, p458
Despite the Sixteenth Directorate's reluctance to share most SIGINT secrets with its intelligence allies, it depended on their assistance. With the growing complexity of computer-generated cipher systems, Soviet cryptanalysts were increasingly dependent on the penetration of foreign embassies to steal cipher materials and, when possible, bug cipher machines and teleprinters. During 1974 alone joint operations by the FCD Sixteenth Department and its Soviet Bloc allies succeeded is abstracting cipher material from at least seven embassies in Prague, five in Sofia, two in Budapest and two in Warsaw. Soviet Bloc intelligence services also shared some of their agents in Western embassies and foreign ministries with the KGB. Among those who were particularly highly rated by the KGB Sixteenth Directorate was a Bulgarian agent codenamed EPIR, a security official in the Greek foreign ministry recruited by Bulgarian intelligence in 1966. Over the next ten years he assisted in the removal of over 12,000 classified pages of documents from the ministry.
From ‘Spycatcher: the candid autobiography of a senior intelligence officer’, p113
After STOCKADE, plans were laid to attack most European ciphers, starting with the Germans. But after much effort, we aborted the operation, because their machines were too well screened. But we successfully placed a probe microphone behind the cipher machine in the Greek Embassy in London. This was a particularly valuable target, since the Greeks were giving considerable support to Colonel Grivas, the Cypriot guerrilla leader, during the Cyprus Emergency.
From 'SOVIET COMINT IN THE COLD WAR' by David Kahn in Cryptologia (Volume 22, Issue 1, January 1998, pages 1-24), p8-9
Kahn’s information comes from an interview with Victor Makarov a translator of Greek intercepts at the KGB’s 16th Directorate. Makarov gives several examples from the messages he translated:
During the Israeli siege of Beirut in August 1982 the Greek ambassador had a meeting with Yasser Arafat who asked for the Greek prime minister Andreas Papandreou to intervene diplomatically.
In 1981 a message from the Washington embassy had details of a meeting between the Greek ambassador and American officials which concerned events in Eastern Europe and especially the Solidarity movement in Poland. The Russians found the information very interesting.
Greek communications security was poor during WWII. It seems that post war this problem was corrected by using cipher teleprinters with OTP tape.
However during the Cold war interested parties were able to sidestep the unbreakable OTP code by using ‘bugs’ and spies.
Small countries should make every effort to protect their communications. Are Greek communications secure today? Probably not.