I feel that we hear a lot about how the Allies (and in particular the Americans and the British) broke through the encryption codes of both the Germans and Japanese, giving them a significant advantage in the war.
What was the opposite like? Did the Germans, Japanese and to a lesser extent, Italians, have any success in breaking Allied encryption systems? If so, did it prove to be a major advantage in specific circumstances?
There were some successes. One particular case was that of the "black Code" which the Italians stole from the US Embassy in Rome. This same code was used by US military attache Bonner Fellers in Cairo to provide continuous updates on the war in North Africa, including ship movements and where the minefields were.
There is a long list of details that were leaked at http://www.historynet.com/intercepted-communications-for-field-marshal-erwin-rommel.htm