Comment by Merrill
9 hours ago
A 1983 review of this remarkable system for the Institute of Electrical and Electronic Engineers (IEEE) attributes no fewer than eight "firsts" to SIGSALY. They are as follows:
1) The first realization of enciphered telephony
2) The first quantized speech transmission
3) The first transmission of speech by Pulse Code Modulation (PCM)
4) The first use of companded PCM
5) The first examples of multilevel Frequency Shift Keying (FSK)
6) The first useful realization of speech bandwidth compression
7) The first use of FSK - FDM (Frequency Shift Keying-Frequency Division Multiplex) as a viable transmission method over a fading medium
8) The first use of a multilevel "eye pattern" to adjust the sampling intervals (a new, and important, instrumentation technique)
From https://www.jproc.ca/crypto/sigsaly1.html
I think that the relevant patents remained classified until 1975.
https://en.wikipedia.org/wiki/SIGSALY#Operation if anyone just wants to get a feeling for how it worked. Pretty good writeup IMO.
OP here, yes, good write up, although I wish someone would code up a simulation that showed it and allowed us to hear what this telephone sounded like to FDR and Churchill.
Supposedly like this: https://www.youtube.com/watch?v=OvR4qK0B--w&t=517s
(I see now that it was already linked elsewhere in the the thread.)
Pretty impressive for cross atlantic one-time pad voice comms in an analogue era, I think. It's amazing what money and smart people can accomplish.
> I think that the relevant patents remained classified until 1975.
If they were classified, they can’t have worked as patents. Patents, by their nature, must be open and available for others to read.
No they don't. There's an exemption in US law for the NSA/the government to file hidden patents which only become revealed when someone else files the same/a similar patent.
Invention Secrecy Act of 1952. https://en.wikipedia.org/wiki/Invention_Secrecy_Act