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)
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.
It was really an awful kludge. Today, you'd think, digitize audio into a bit stream, encrypt bitstream. That's not how it worked. It was somewhat similar to the older A-3 analog scrambler, which split up audio into a number of bands and rearranged them, changing the rearrangement occasionally. In SIGSALY, incoming audio was filtered out into 10 frequency bands.
There was also a dominant pitch detector and a "hiss" detector for unvoiced content.
That created 12 analog signals to encrypt. Those signals were much lower bandwidth than the original speech. The patent seems to indicate that the frequency band signals were merely encoded as above or below a threshold. Not a full A/D, just a 1-bit threshold. As late as 1973, people were still trying vocoder-like technologies, but it became easier to work on audio in the digital domain and that died out.[2]
The keying system changed the key every 20ms. It's not clear from the description whether the digitization of the 12 signals was also one sample for 20ms, but it probably was. If you used the same key bits for more than one analog sample, that would create a vulnerability. It's a one time key system, and those only work against serious opposition if the key is only used once. See VENONA.
The articles indicate that synchronizing the key stream, which was on phonograph records, was a huge synchronization headache. Keeping signals in sync was really hard, and was part of the curse of analog TV, with horizontal and vertical hold controls.
What this looks like is a system which had to work regardless of cost. So it was put together out of known building blocks. Straight digitization of audio was probably considered, especially since Alec Reeves, who had demoed pulse code modulation in 1937, was involved.
But it was a high-risk technology. They would have had to invent a good A/D converter and a decent modem, which would have added technical risk to the project.
It's one of those systems of historical interest because it was too soon. You couldn't really do the job in the straightforward way, but it needed to be done, resulting in a magnificent kludge.
> a pair of vinyl phonograph records, each containing identical-but-random noise.
> These were the (single-use) keys to the encryption and decryption process.
> Then they set their identical records spinning at the exact same moment. On each end, the voices of these two world leaders are threaded through the SIGSALY terminal, mixed with a layer of noise, sent across the ocean via shortwave radio, then re-synthesized in a reverse process.
> Anyone attempting to listen in on the calls would just hear a buzzing sound, which is how the system earned one of its nicknames: “The Green Hornet,”
> At the end of each conversation, the records were destroyed to protect against potential future decryption.
I wonder if with todays tech we could decrypt this. This sounds really close to a one-time pad (if the conversation was kept shorter than each record) so .. probably not? Unless their random noise wasn't as random, or if the mixing of random + voice would leave other tell-tale signs?
Definitely a one time pad - and therefore the answer to your question is "it depends on the randomness used". Sound sometime has surprising decryption properties in that starting and stopping long runs of data isn't always obscured properly by some schemes, so I'd also say "it depends on the exact scheme used for the frequency shifting."
This was at the dawn of the age of modern information theory, built on the shoulders of giants, but there are often some subtleties.
An example: if we imagine the encryption is perturbing a waveform +/- 30% of its frequency and amplitude at any one time, the encrypted bitstream is likely totally intelligible to the ear when replayed, even if reconstructing the exact bitstream is difficult.
Another example - if you make a block cypher that relies on prior blocks to seed randomness, then encrypting say 1,000 sequential blocks of zeros is very likely going to have some structure to it unless you've specifically designed it not to.
I'd love to hear some waveforms of what these calls sounded like encrypted -- it would be a fun project to work on decrypting them with modern tech.
Might be able to re-produce the signal in GNU Radio, I think there might be enough information in the Wikipedia article about how the modulation and encryption worked to get something similar going. The actual voice that came out was barely understandable lol: https://www.youtube.com/watch?v=OvR4qK0B--w&t=517s
> Each terminal cost $1 million (at 1943 values) and weighed more than 50,000 kg (50 tonnes). The first one was housed in the Pentagon, with an extension to the White House. A further 11 terminals were installed at different sites around the world, including one in the sub-sub-basement of Selfridges department store in central London
I've learned that I tend to underestimate how large inflation is for historical values, so I looked this up. $1 million in 1943 is apparently just under $19.5 billion today, which means the full set cost $234 billion. I'm not sure if the US foot the bill for all of them or not, but to make it more concrete, 44 of these would have cost more than entire budget for the Department of Defense for this year.
Others noted this should be $19m, not billion. That said, often a more useful analysis is percent of GDP -- this can give a sense of what fraction of effort of the total economy went into it. On those terms, 1943 GDP: $200bn, 2025 GDP: $30tn, for an increase of 150x.
So, depending on how you count, these were $19-150m each in today's dollars, or between 1/10 and 1/3 of an ASML EUV machine.
Yeah, I honestly wouldn't have commented at all if I had avoided such an embarrassing reading comprehension mistake, since the correct number is not particularly interesting.
My lesson for today is not to trust my ability to count comma separated digit groups.
1 mil seems like an arbitrary or at least rounded number, and also it's not like you could get one on the market, so maybe it actually didn't cost a million
Crap, today is not my day for reading comprehension I guess (combined with overcorrection for my anticipated error). Too late for me to edit, but thank you for pointing this out.
I know this is a bit offtopic, but shouldn't the title say "the President of the United States," since 1) Churchill is UK's Prime Minister, and Roosevelt is not his President and 2) the publication on which this article appears is from the UK?
If the article itself (seemingly from the UK, as you point out) is inclined to assume that it's fine to describe it this way, I don't see why those of us from the rest of the world (which I'm inferring from your username is a group you're a part of) should object.
Even the original UK article just says "the President". Things may change as the US may not play the leading role in this century as it did the last, but despite many countries having presidents (although not the UK), it is still understood that "the President" means POTUS.
I think historic context provides enough clarity for readers of the website of the imperial war museum.
I also think the headline as is would be good enough even for people who might not have learned about ww2 yet. A headline is not meant to be a complete summary after all...
This is briefly mentioned in Neal Stephenson's Cryptonomicon. The book is well worth a read if you don't mind viewpoint shifts and slightly hokey historical spec-fic.
It's a slightly alternate universe. It's not quite our world, it just looks kind of like it from a distance. Qwghlm isn't really Skye and Lewis, it's like if you kind of wodged the Falklands and the Isle of Man into the same space.
Some of the people are kind of the same but not quite.
But from way over here, you'd be hard pushed to spot the differences, unless you looked annoyingly closely.
IIRC from Prof: Alan Turing Decoded, Turing was sent to the US to work on this for a while, but wasn't able to contribute much, because the Americans didn't really trust him.
Wikipedia says 'precise clocks' which I would guess was quartz clocks on the back of radio synchronization. It was definitely well within the capabilities of the scientists of this period to precisely calibrate against radio wave time delays from London, Australia, etc.
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.
> 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
Here's the technical description, from NSA.[1]
It was really an awful kludge. Today, you'd think, digitize audio into a bit stream, encrypt bitstream. That's not how it worked. It was somewhat similar to the older A-3 analog scrambler, which split up audio into a number of bands and rearranged them, changing the rearrangement occasionally. In SIGSALY, incoming audio was filtered out into 10 frequency bands. There was also a dominant pitch detector and a "hiss" detector for unvoiced content. That created 12 analog signals to encrypt. Those signals were much lower bandwidth than the original speech. The patent seems to indicate that the frequency band signals were merely encoded as above or below a threshold. Not a full A/D, just a 1-bit threshold. As late as 1973, people were still trying vocoder-like technologies, but it became easier to work on audio in the digital domain and that died out.[2]
The keying system changed the key every 20ms. It's not clear from the description whether the digitization of the 12 signals was also one sample for 20ms, but it probably was. If you used the same key bits for more than one analog sample, that would create a vulnerability. It's a one time key system, and those only work against serious opposition if the key is only used once. See VENONA.
The articles indicate that synchronizing the key stream, which was on phonograph records, was a huge synchronization headache. Keeping signals in sync was really hard, and was part of the curse of analog TV, with horizontal and vertical hold controls.
What this looks like is a system which had to work regardless of cost. So it was put together out of known building blocks. Straight digitization of audio was probably considered, especially since Alec Reeves, who had demoed pulse code modulation in 1937, was involved. But it was a high-risk technology. They would have had to invent a good A/D converter and a decent modem, which would have added technical risk to the project.
It's one of those systems of historical interest because it was too soon. You couldn't really do the job in the straightforward way, but it needed to be done, resulting in a magnificent kludge.
[1] https://www.nsa.gov/portals/75/documents/about/cryptologic-h...
[2] https://www.youtube.com/watch?v=UfpUexWJqb4
> a pair of vinyl phonograph records, each containing identical-but-random noise. > These were the (single-use) keys to the encryption and decryption process.
> Then they set their identical records spinning at the exact same moment. On each end, the voices of these two world leaders are threaded through the SIGSALY terminal, mixed with a layer of noise, sent across the ocean via shortwave radio, then re-synthesized in a reverse process.
> Anyone attempting to listen in on the calls would just hear a buzzing sound, which is how the system earned one of its nicknames: “The Green Hornet,”
> At the end of each conversation, the records were destroyed to protect against potential future decryption.
I wonder if with todays tech we could decrypt this. This sounds really close to a one-time pad (if the conversation was kept shorter than each record) so .. probably not? Unless their random noise wasn't as random, or if the mixing of random + voice would leave other tell-tale signs?
Definitely a one time pad - and therefore the answer to your question is "it depends on the randomness used". Sound sometime has surprising decryption properties in that starting and stopping long runs of data isn't always obscured properly by some schemes, so I'd also say "it depends on the exact scheme used for the frequency shifting."
This was at the dawn of the age of modern information theory, built on the shoulders of giants, but there are often some subtleties.
An example: if we imagine the encryption is perturbing a waveform +/- 30% of its frequency and amplitude at any one time, the encrypted bitstream is likely totally intelligible to the ear when replayed, even if reconstructing the exact bitstream is difficult.
Another example - if you make a block cypher that relies on prior blocks to seed randomness, then encrypting say 1,000 sequential blocks of zeros is very likely going to have some structure to it unless you've specifically designed it not to.
I'd love to hear some waveforms of what these calls sounded like encrypted -- it would be a fun project to work on decrypting them with modern tech.
Might be able to re-produce the signal in GNU Radio, I think there might be enough information in the Wikipedia article about how the modulation and encryption worked to get something similar going. The actual voice that came out was barely understandable lol: https://www.youtube.com/watch?v=OvR4qK0B--w&t=517s
> Each terminal cost $1 million (at 1943 values) and weighed more than 50,000 kg (50 tonnes). The first one was housed in the Pentagon, with an extension to the White House. A further 11 terminals were installed at different sites around the world, including one in the sub-sub-basement of Selfridges department store in central London
I've learned that I tend to underestimate how large inflation is for historical values, so I looked this up. $1 million in 1943 is apparently just under $19.5 billion today, which means the full set cost $234 billion. I'm not sure if the US foot the bill for all of them or not, but to make it more concrete, 44 of these would have cost more than entire budget for the Department of Defense for this year.
Others noted this should be $19m, not billion. That said, often a more useful analysis is percent of GDP -- this can give a sense of what fraction of effort of the total economy went into it. On those terms, 1943 GDP: $200bn, 2025 GDP: $30tn, for an increase of 150x.
So, depending on how you count, these were $19-150m each in today's dollars, or between 1/10 and 1/3 of an ASML EUV machine.
Yeah, I honestly wouldn't have commented at all if I had avoided such an embarrassing reading comprehension mistake, since the correct number is not particularly interesting.
My lesson for today is not to trust my ability to count comma separated digit groups.
1 mil seems like an arbitrary or at least rounded number, and also it's not like you could get one on the market, so maybe it actually didn't cost a million
For comparison, the unit cost of Boeing B-29 Superfortress (manufactured 1943–1946) was $639,188. In total 3,970 B-29s were build.
https://en.wikipedia.org/wiki/B-29
No, inflation it's $19,476,300 in today's dollars. 19 million not billion.
You're an order of magnitude off: $1M in 1943 is ~$19.5M today.
https://www.bls.gov/data/inflation_calculator.htm
Crap, today is not my day for reading comprehension I guess (combined with overcorrection for my anticipated error). Too late for me to edit, but thank you for pointing this out.
I know this is a bit offtopic, but shouldn't the title say "the President of the United States," since 1) Churchill is UK's Prime Minister, and Roosevelt is not his President and 2) the publication on which this article appears is from the UK?
If the article itself (seemingly from the UK, as you point out) is inclined to assume that it's fine to describe it this way, I don't see why those of us from the rest of the world (which I'm inferring from your username is a group you're a part of) should object.
Even the original UK article just says "the President". Things may change as the US may not play the leading role in this century as it did the last, but despite many countries having presidents (although not the UK), it is still understood that "the President" means POTUS.
The UK doesn't have a president, so it normally refers to the US president in general context.
I think historic context provides enough clarity for readers of the website of the imperial war museum.
I also think the headline as is would be good enough even for people who might not have learned about ww2 yet. A headline is not meant to be a complete summary after all...
Anyone decoded SIGSALY correctly yet, is it signals ally?
Read on (in TFA):
> It came to be known as SIGSALY
This is briefly mentioned in Neal Stephenson's Cryptonomicon. The book is well worth a read if you don't mind viewpoint shifts and slightly hokey historical spec-fic.
> slightly hokey historical spec-fic.
It's a slightly alternate universe. It's not quite our world, it just looks kind of like it from a distance. Qwghlm isn't really Skye and Lewis, it's like if you kind of wodged the Falklands and the Isle of Man into the same space.
Some of the people are kind of the same but not quite.
But from way over here, you'd be hard pushed to spot the differences, unless you looked annoyingly closely.
A great example of a one-time pad!
There is an illustration for the encryption process in Appendix B here: https://www.nsa.gov/portals/75/documents/about/cryptologic-h...
There was a 99% invisible episode on this [0]. I recall there being some good audio examples.
[0] https://99percentinvisible.org/episode/vox-ex-machina/
Two turntables and a microphone... https://www.youtube.com/watch?v=1_4Jjm3MMiU
Also, worth reading about is Turing's Delilah speech encryption system: https://spectrum.ieee.org/alan-turings-delilah
For anyone interested in this stuff - “Battle of Wits” is a great book about cryptanalysis in WW2.
Thanks, now I know what I'm going to read next
IIRC from Prof: Alan Turing Decoded, Turing was sent to the US to work on this for a while, but wasn't able to contribute much, because the Americans didn't really trust him.
Does anyone know how they synchronized the time? Was a radio signal fast enough?
Wikipedia says 'precise clocks' which I would guess was quartz clocks on the back of radio synchronization. It was definitely well within the capabilities of the scientists of this period to precisely calibrate against radio wave time delays from London, Australia, etc.
* US president