Les poisons du KGB

Protecting secrets: British diplomatic cipher machines in the early Cold War, 1945–1970

“…Noskeno, who defected to the United States in 1964, did report that there were 'some successes' in decrypting British communications but he could not remember any specific examples and may not have been referring to machine encrypted diplomatic traffic. 68 It is possible though to examine the ways in which foreign intelligence services (and especially the KGB) might have attacked the ciphers and look for any obvious failings in British cryptographic security. There were three main approaches that an intelligence service could have taken at this time: it could intercept British diplomatic telegrams and seek to solve the cipher through pure cryptanalysis, applying mathematical techniques and linguistic analysis; it could try to obtain the cipher machines and cryptographic materials, such as key lists and key tapes.…”