If your radio resume extends back into the days of the Cold War and the German call signs DFC37 and DFD21 sound familiar, then you will want to check out the link below.
From the link: "The translation of an in-house research paper of the communist Polish counterintelligence depicting the ciphers and the one-way radio communications patterns used by the U.S. and West German intelligence services against Poland in the 1960s and early 1970s is presented."
This material appeared in an edition of Cryptologia and shows how the number transmissions were decrypted if you had the one time pads and in some cases the codebook.
"The agent management behind the Iron Curtain posed several problems to the western intelligence services during the Cold War. Because of security considerations, the safest way to communicate with the agent was through non-personal manners such as dead drops, invisible ink letters, or radio. In addition, the messages were encrypted to provide security.
"While the letters could be opened and read by the enemy and the officers, for example, working under diplomatic cover could be captured while filling or emptying the dead drops in a hostile country, the one-way high frequency (HF) radio communications provided an ultimate solution to the security issues while controlling the assets on unfriendly soil. First, the commercial receiver could be possessed even in oppressive regimes without causing suspicion. Second, it was almost impossible for enemy counterintelligence to detect the instances when an agent was listening to the broadcasts unless the person was under tight surveillance or the counterintelligence was monitoring the radio spectrum in close distance from the agent's receiver at work. Third, the agents did not need long and laborious training in radio communications, for they were simply to copy the cipher text and decrypt it according to prearranged schemes. More attention could therefore be granted to the ciphers and the decryption process.
"The agent broadcasts took the form of groups of numbers transmitted in voice or telegraphy on HF bands in the various languages of the world, hence their transmitters are known as “numbers stations.” Such a way of controlling the assets in socialist countries, especially Poland, was implemented by western intelligence services during the Cold War, as evidenced by the presented document."
You can read more of this fascinating document online at http://www.swldxer.co.uk/polish.mht
