alt Hacker News> 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.