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I was wondering how the allied (America and England, since France was occupied by the Nazis) communicated securely with each other in 1943. I know that the SIGSALY existed, but I am most interested in how Roosevelt's and Churchill's telegrams were encrypted. Did they use the British Typex or the American SIGABA?

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    Totally mandatory reading material: Neal Stephenson - Cryptonomicon – fho Dec 11 '14 at 9:57
  • @tho I have issues with some of the techniques described in the book; particularly when they describe how they use white noise to encrypt a voice call... given a non trivial delay in the signal (IIRC it was a call from Australia to UK), I doubt the setup would have worked. – SJuan76 May 8 '15 at 9:17
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The communications between national leaders are normally conducted through the embassies. I.e., Churchill would send a Typex-encrypted telegram to the British Embassy in Washington, DC, it is decrypted there, and delivered in person to the White House. Similarly, Roosevelt would send a SIGABA-encrypted message to the US Embassy in London, it is decrypted there and delivered in person to Number 10. (Cold War required faster decision making, necessitating Moscow-Washington hotline).

The direct communications between the militaries were conducted via Combined Cipher Machine starting 1943-11-01.

The machine looked like a typewriter (all of them did, including Enigma) and was operated by a technician.

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