Neighbors: A New History of Soviet Intelligence. Macmillan. pp. 29 (cryptography), 61 (logistics), 62 (Sorge + Noulens), 69 (Philby), 70 (Deusch). https://books
German High Level Cryptography and Cryptanalysis, p.73. ^ a b c d TICOM Investigations Volume2 - Notes on German High Level Cryptography and Cryptanalysis