[HN Gopher] Alan Turing's "Delilah" project
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Alan Turing's "Delilah" project
Author : pseudolus
Score : 136 points
Date : 2025-02-04 14:50 UTC (8 hours ago)
(HTM) web link (spectrum.ieee.org)
(TXT) w3m dump (spectrum.ieee.org)
| teeray wrote:
| I remember something like this was used in Cryptonomicon. It's
| been almost two decades since I read it, but IIRC it was a phone
| conversation between Churchill and FDR that was secured with twin
| one-time-pads encoded on vinyl records.
| jgrahamc wrote:
| See: https://en.wikipedia.org/wiki/SIGSALY
| convolvatron wrote:
| I assumed also that this must of been done in some odd way in
| the analog domain, but apparently it was digital audio
| Animats wrote:
| Not really digital. The "combining unit" seems to have been
| an analog adder that wraps. The key generation was mechanical
| and digital, and produced an analog key waveform to add to
| the voice signal. At the other end,the analog waveform was
| subtracted out. Keeping both ends in sync would have been the
| main problem.
|
| If it was a real A to D with digital encryption, it would
| have needed far more tubes. The digital side would have had
| to be all electronic. It wasn't. Look at the picture. That's
| an Enigma mechanism with a very few tubes out back.
|
| Something like that would have sync problems. Not clear what
| they used as a time base for the demo device. Maybe for demo
| purposes they just used the power line as a clock.
|
| Before SIGSALY, there was a pre-war Western Electric system,
| the A-3 [1], used for transatlantic phone calls. That had
| only five channels, advanced the key only every 15-20
| seconds, and only had six channel-swapping patterns. The A-3
| was a very low grade encryption system, and was broken by the
| Germans.
|
| SIGSALY was the A-3 concept scaled up. More channels, faster
| key changes, additional analog processing. It filtered analog
| voice into ten channels, and swapped the channels around
| based on a one-time key stored on phonograph records. This
| seems to have taken way too much hardware. But it had
| redundancy, each direction was separate, and there was a
| pseudorandom key generator for testing without using up one-
| time keying material, all of which added bulk.
|
| Audio speed analog to digital converters were invented in
| 1937 by Alec Reeves.[2] But they were not used until after
| WWII. A usable voice-speed A to D seems to have been beyond
| the capabilities of WWII electronics. Reeves had the basic
| concept - a counter, a ramp generator, and a comparator. All
| of those were very hard to do in 1937.
|
| Reeves is an obscure figure. He invented pulse-code
| modulation as well as the A to D converter. He spent WWII
| working on aircraft navigation systems rather than
| encryption. If he'd been involved in encryption, high-
| security WWII voice encryption probably would have been all-
| digital. After the war, he was involved in the beginnings of
| fiber optic links, so he did quite a bit.
|
| [1] http://chris-intel-
| corner.blogspot.com/2012/02/intercepted-c...
|
| [2] https://en.wikipedia.org/wiki/Alec_Reeves
| jpm_sd wrote:
| Delilah was the far superior system Turing never quite got to
| productionize, while the low-fi "Project X" was actually used
| for conversations between world leaders.
|
| https://en.wikipedia.org/wiki/SIGSALY
| jgrahamc wrote:
| I suppose some of this is a "lost story" but I wrote about
| Delilah back in 2012: https://blog.jgc.org/2012/03/delilah-
| secure-speech-system.ht... and the actual system is on display at
| Bletchley.
| world2vec wrote:
| Great read but have a slightly off-topic question:
|
| What is your opinion on visiting Bletchley Park? Is it worth it?
| Or is it more oriented to kids and whatnot?
| tialaramex wrote:
| In this context it's important to know that there are _two_
| museums at Bletchley and they aren 't entirely co-operative
| with each other. There's The National Museum of Computing
| https://www.tnmoc.org/ and there's also Bletchley Park's museum
| https://bletchleypark.org.uk/ these are both on the same
| physical site, in the grounds of the Bletchley Park stately
| home because that's where Ultra happened in WW2
|
| Both museums do have some kid-friendly activities, but their
| focuses are very different. You might wish to visit one, or
| both, and you should figure that out _before_ going as they
| aren 't even necessarily open at the same time.
|
| TNMOC is about Computers generally, but has some exhibits about
| Enigma including a Bombe reconstruction and then of course
| Colossus - to break the Lorenz cipher, only exists due to the
| war and would have been at Bletchley. If you don't much care
| about Computers that's not too interesting, maybe worth a half
| hour if you've time.
|
| The main Bletchley Park museum is about Codebreaking and
| particularly Ultra, the secret project to break German codes,
| most famously Enigma but also Lorenz and others, at Bletchley
| Park in WW2. It has some exhibits about spycraft, and a lot
| more about the practical undertaking of this codebreaking. Who
| are these people, what are they all doing here, what was their
| life like? If you care about the _people_ you will want to
| visit this museum, but it has relatively little about the
| technical nuances of what was done.
| ggm wrote:
| It's probably gone now, but rather bizarrely there was a
| harrier jump jet parked on a patch of green grass when I was
| last there some years ago. Sort of "dumped, pending working
| out how to deal with it" which made me feel like nobody runs
| the place and everyone runs the place. "Joe said I could"
| -"oh OK put it over there then"
|
| Another thing about the place is that modern archeology
| doesn't favour restoration of everything. Limited amounts of
| structural change happen. So a lot of the site looks like
| dismal ww2 badly poured concrete, not well looked after.
| Since GCHQ occupied the space for some time, some of it is
| probably post war, and historically relevant to different
| stories.
| mikewarot wrote:
| The incoming signal is turned into 4000 bits per second then
| XORed with a large pseudorandom sequence.[1]. It's quite
| interesting what was possible given such limited hardware at the
| time.
|
| I've seen multivibrators as frequency dividers in the repair work
| I've done. The clever thing here would be in the initialization,
| and synchronization at the receive end. I'd imagine that wheel
| has to be spun up to some fraction of 4000 rotations/second and
| uses photodiodes or perhaps just contact, to generate the
| starting pulses.
|
| [1] https://www.turing.org.uk/sources/delilah.html
| ASalazarMX wrote:
| I'm frequently amazed how technological advance frequently is
| making things smaller/faster/cheaper, not inventing or
| discovering them in the first place.
| mystified5016 wrote:
| True innovation is very expensive and very risky. It's
| unpalatable to most companies, so the best we've got is
| incremental improvements.
| rsynnott wrote:
| Slightly weirdly worded:
|
| > Bell Labs' pioneering SIGSALY speech-encryption system was
| constructed in New York City, under a U.S. Army contract, during
| 1942 and 1943. It was gigantic, weighing over 50 thousand
| kilograms and filling a room. Turing was familiar with SIGSALY
| and wanted to miniaturize speech encryption.
|
| Well, yes; given that he _helped design it_
| (https://en.wikipedia.org/wiki/SIGSALY#Development) he probably
| would be familiar with it.
| cubefox wrote:
| > Work on the Delilah project stopped not long after the war
| ended, when Turing was hired by the British National Physical
| Laboratory to design and develop an electronic computer. Delilah
| "had little potential for further development," Bayley said and
| "was soon forgotten." Yet it offered a very high level of
| security, and was the first successful demonstration of a compact
| portable device for voice encryption.
|
| That seems curious -- surely the military would have been
| interested in a finished portable voice encryption system, even
| after the war?
| dang wrote:
| One small past thread:
|
| _Alan Turing - The Delilah Project_ -
| https://news.ycombinator.com/item?id=38862147 - Jan 2024 (7
| comments)
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