Good Resources on Voice Encryption?

GSM is this: https://en.wikipedia.org/wiki/A5/1 (over the AMR codec). The 3GPP docs are generally available if you want to get very, very technical about the mobile network.

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.

The mumble protocol is a nicely documented example for using encrypted Opus (OCB-AES128) over UDP: http://mumble-protocol.readthedocs.io/en/latest/voice_data.h...

Look at some of the narrow band radio standards. P25 standards are not freely available, but DMR standards can be freely downloaded from ETSI [1]. P25 with 56-bit DES is well and truly broken, but I gather 256-bit AES is still okay. Also look at the signal protocol?

[1] https://www.etsi.org/technologies/mobile-radio

What exactly are the challenges of voice encryption over say text encryption? Just the bandwidth of data, or establishing trust?

https://www.gstatic.com/duo/papers/duo_e2ee.pdf is a paper on video encryption by duo. It is pretty good. I assume the audio encryption problem is only a subset of this problem.

I remember being on the old Sprint CDMA network, you could dial ##VPON# and it would encrypt your connection to the tower[1] but was disabled by default. Dunno if that still works (I no longer live in the US, and EVDO isn't a thing anymore).

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:

[1] https://bestcellular.com/dial-codes/

I don't have anything specific.

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.

I would suggest a basic how-to on setting up SRTP/SIPS for e.g. an Asterisk setup - it's not overly complicated, based on my own experience running a community PBX many years ago.

If you want to start at the very beginning, look into SIGSALY.

https://en.wikipedia.org/wiki/SIGSALY