Ask HN: Good Resources on Voice Encryption?
Any textbooks, very technical stuff is recommended. Both, VoIP and Cellular networks.
Generally any combination of a constant-bitrate low-latency voice codec with a cipher in XOR stream mode should work. If the codec does "comfort noise" you should disable that to keep the bitrate constant during silence.
I haven't tried, but I'd think encrypting and decrypting a packet would take less than 0.1ms, no?
What's the variation in the structure of the data? Wouldn't you just encrypt and send a fixed-length interval of audio each period?
So for voice encryption, you need to obscure all that through artificial jitter and noise, and lack of compression in strategic places. It is a complex topic and I'm not sure the science is settled beyond "skipping compression helps".
There is something to be said about the volume of data being sent during silence; but, uncompressed audio shouldn't have that problem; and, for audio that does, there could be filler data to maintain a given bitrate across the line.
Really transmitting the zeroes as they are is just transmitting uncompressed PCM, which is the trivial solution. Adding filler is undoing most of the compression. The hard part is to add just enough filler, jitter and confusion for an attacker to be sufficiently blinded while maintaining an acceptable compression ratio.
Really? Would I not just get a not quite constant stream of (unencrypted) data that‘s small enough to send at a low bandwidth? And when that data arrives at less than the maximum bandwidth of the channel that I actually use, I just add some filler. And then I encrypt that now really constant stream of data.
So, no. The filler is part of the protocol and is not undoing any of the PCM compression; silence would let you compress the stream more than the plain voice codec would - and THAT would interact with encryption. But that’s quite unusual for real time systems.
Yes, one often does CBR, but even there, variable difficulty of compression often produces variable jitter, which can then be used to infer information about the plaintext stream. There are constant runtime CBR codecs, but one has to take care to use them.
So e.g. maybe you're doing 48kbps, the codec would still consume 48000 bits per second for silence. However if a radio link layer indicates it's struggling to move 48000 bits per second that "adaptive mode" audio codec could shift down to 36kbps instead. This is likely to be a much better user experience than throwing away 25% of your compressed audio due to packet loss and then trying to reconstruct it.
For something like Opus you can gracefully degrade this way from 48kbps (transparent for voice) to 8kbps (non-transparent but easily understandable) without an eavesdropper learning anything about the content, they only get insight into whether you've got link trouble.
Says if you don’t and simply XOR an audio with PRNG output, the resultant entropy will not be constant and transmission sounds like a noisy radio. Something like that.
What's the variation in the structure of the data? Wouldn't you just encrypt and send a fixed-length interval of audio each period?
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Historically voice encryption was politically only meant for state use, with strict controls, and us plebs not getting any voice encryption or very weak encryption only. Compared to encryption on the internet, this state has persisted for longer in communications. Even in new communication standards the options for encryption generally offer weak/irrelevant security for modern standards (end-to-end encryption).
I'm fairly certain Cell networks are not encrypted at all, by default. Or at least it's disabled completely by the towers in Afghanistan. :whistling:
This is patently false, while some networks did allow no encryption (A0 on GSM for example), pretty much everything on UMTS/LTE is encrypted at least to the tower.
> In 2006 Elad Barkan, Eli Biham and Nathan Keller demonstrated attacks against A5/1, A5/3, or even GPRS that allow attackers to tap GSM mobile phone conversations and decrypt them either in real-time, or at any later time
You could look for resources that cover digital HAM radio operation. They should have some stuff about the basics of voice encryption. Most of it is not secure until you get to high-end stuff like Motorola AES 256. Some of this 'encryption' is just privacy codes (cell networks are not encrypted but use digital privacy codes I think).
Once you digitize the voice, then it should be pretty much regular encryption.
https://www.amateurradio.com/encryption-is-already-legal-its...
Like I said in my original post, you can look into encryption in the amatuer bands. This article is one example. If you've taken encryption courses then you know that XOR can be a cipher, it's just not secure. The same way a lock on your shed is only going to keep curious people out and not real criminals, the same can be said for lesser forms of encryption.
Please look into Kenwood AES/DES models that operate in the VHF/UHF amatuer bands if you still have any doubts about the use of encryption. There are various 40, 56, etc bit encryption schemes as well.
Over on HF, digital modes like FT8 are quite popular. You will never be able to decode that without a computer, but that doesn't make it illegal (or encrypted). The algorithm is well defined and it's ~100x more bandwidth efficient than SSB voice.
Kenwood sells AES radios for non-amateur communications. It's perfectly legal for non-amateur licensees to encrypt their radio links. Your cell phone is doing it right now!
Yes, you can use those on the amateur bands if you want. It's against the rules. The reason amateur radio exists is because we follow the rules. It can all disappear overnight if you violate them. There are a few well-known bad apples that make it harder for all of us. It's not to be encouraged.
I'm not advocating that they use true encryption in the ham bands, but it does exist. As I said before, there is information out there about how voice is digitized, how psuedo or weak encryption works (DMR, 40 bit, 56 bit), and then you can use standard encryption practices to encrypt it.
The OPs question was about where he can find technical info on encrypting voice communications and I said this would be a good starting point. This is a valid contribution to his question. I am sorry if you do not believe that weak encryption (where you know all possible keys, or the keys are small) is not encryption.
Yes they do. Decades ago they didn't. Today there are devices that use active attacks to downgrade the encryption by impersonating a base station.
It's also possible to crack the encryption used by GSM, but I believe the base station impersonation attacks are much more common.
I believe they are not encrypted, but use a few thousand channels on a trunked system.
For a long time the audio codec was only available in a chip (technically a readout protected microcontroller). There are patents on the audio codec, but they didn't disclose enough of it to decode it, only enough to make it unlawful for other people to publish compatible implementations (which, of course, kept the resources available for reverse engineering low).
For a while I contemplated selling bespoke custom versions of Opus as a bit of performance art under licensing where the first copy cost $500 and all further copies cost $1,000,000 with some marketing copy about keeping lids off your repeaters. ... just to see how the FCC would react.
Considering that they let AMBE use get away with it, as the old joke goes: We've already established what kind of licensing regime they'll permit-- pay to access encrypted audio-- my performance art differed only by the price.
:)
> The reason amateur radio exists is because we follow the rules. It can all disappear overnight if you violate them. There are a few well-known bad apples that make it harder for all of us. It's not to be encouraged.
Personally, particularly on bands above 70cm, I think the prohibition against encryption is killing amateur radio. The lack of encryption for signals that would be naturally point to point anyway and disturb no one inhibits a lot community use, and the relative non-usage of these allocations risks use losing them.
I'd much rather see a rule that allowed encryption on 33cm+ subject to the constraint that stations have to be identified, non-profit in nature, cooperate with local coordination, and act as secondary users to non-encrypted uses.
Yes, I think it is reasonable, although I don't know what bands to have that on, and of course it should not be interfering with non-encrypted uses.
(And perhaps the same rule should be applied to proprietary codecs, too, so that they don't overload the radio with proprietary codes that you cannot figure out how to decode.)
As an American this sort of sentiment is absolutely depressing to see. It seems to be incredibly common in a number of areas - radio, flight, and chemistry, to list just a few. I can only hope access to unencumbered computers doesn't fall victim to the same.
WTF happened to our supposed ideal of freedom?