State Department cipher machines and communications security in the early Cold War, 1944-1965

From 1944 the State Department attempted to improve its communications security by creating a Division of Cryptography and mechanising the encryption process. This article assesses the effectiveness of these reforms and shows that State's new cipher equipment had cryptographic vulnerabilities. Moreover, the department was unable to maintain physical security at the Moscow embassy and through espionage and technical surveillance the KGB broke the ciphers and read American communications. The paper concludes by analysing the impact of this security failure, including the claim that intercepted messages influenced Stalin's decision to approve the North Korean invasion of South Korea in 1950.