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The Transoceanic crypto system Shannon created so Churchill & Roosevelt could conference call was brilliant. It was a sonic one-time pad, L.P.s were sent to Br

by deepnet 10y ago

The Transoceanic crypto system Shannon created so Churchill & Roosevelt could conference call was brilliant. It was a sonic one-time pad, L.P.s were sent to Britain and America. They were played over the conversation, simply adding noise - precisely calibrated by Shannon's signal to noise ratio formula. The noise was subtracted at the other end, but any eavesdroppers on the transatlantic cable would have been unable to listen without the L.P.s and circuitry. So while Enigma was being cracked at Bletchly Park, Churchill and Roosevent could chat on the phone, provable securely.

keithpeter 10y ago
Anyone tried a demo of this one with (say) Audacity generated noise sample and a few words mixed well down then 'decoded'? Would be fun to see how far you could degrade the encoded voice recording before decoding became problematic.
- deepnet 10y ago
  That sounds worth a go, although Shannon's system was analogue rather than digital which might have made a difference to the point where signal is unrecoverable from noise. Then there is the noise from the transatlantic cable.
  - keithpeter 10y ago
    "Then there is the noise from the transatlantic cable." Sure would be, and then there would be severe bandwidth limitations, frequency dependent phase delays and so on. I can remember transatlantic cable telephone calls in 1960s/1970s (I was a small boy at the time) and they sounded like the Daleks. That is the interesting bit: US President says stuff into microphone and we have (President + Local Recorded Noise) convolved with Transatlantic cable = Input Then we have Churchill in his Siren Suit with a brandy or three playing his noise LP (I gather that they were 16" acetates at 78rpm) Input - Local Recorded Noise = something like President. I'll have a play over the weekend: just how bad can the transatlantic cable get before you lose the signal?

by deepnet 10y ago

keithpeter 10y ago

Anyone tried a demo of this one with (say) Audacity generated noise sample and a few words mixed well down then 'decoded'? Would be fun to see how far you could degrade the encoded voice recording before decoding became problematic.

deepnet 10y ago
That sounds worth a go, although Shannon's system was analogue rather than digital which might have made a difference to the point where signal is unrecoverable from noise. Then there is the noise from the transatlantic cable.
- keithpeter 10y ago
  "Then there is the noise from the transatlantic cable." Sure would be, and then there would be severe bandwidth limitations, frequency dependent phase delays and so on. I can remember transatlantic cable telephone calls in 1960s/1970s (I was a small boy at the time) and they sounded like the Daleks. That is the interesting bit: US President says stuff into microphone and we have (President + Local Recorded Noise) convolved with Transatlantic cable = Input Then we have Churchill in his Siren Suit with a brandy or three playing his noise LP (I gather that they were 16" acetates at 78rpm) Input - Local Recorded Noise = something like President. I'll have a play over the weekend: just how bad can the transatlantic cable get before you lose the signal?