Is it even possible on android? Is there a FOSS dialer to optionally encrypt some phone calls (non voip) using a pre-shared key with other party?
Is it even possible on android? Is there a FOSS dialer to optionally encrypt some phone calls (non voip) using a pre-shared key with other party?
See : https://en.m.wikipedia.org/wiki/Secure_voice
It’s all about bandwidth. At a minimum cellular voice signals have 4.7 kilobits of bandwidth per second.
Plus the cell phone network and the cell phones themselves, work really really hard, at compressing that data stream for human voices only.
So if you’re going to use some acoustic coupling to send data acoustically over the cellular network, you’re not going to get 4.7 kilobits per second, you’re going to get less than that.
Encrypting your voice stream, is going to take some bandwidth, so let’s say there’s a 10% overhead, so we’re at about 4 kilobits per second of total voice bandwidth after encryption.
http://www.whence.com/minimodem/ is a neat program that does software audio encoding and decoding so you could run a virtual modem from your desktop or phone.
Here is a demonstration of the general concept: https://www.youtube.com/watch?v=uQqWHLZjOjA
https://spectrum.ieee.org/why-mobile-voice-quality-still-stinksand-how-to-fix-it
Here is some secure voice modulation demonstrations that you could use as a starting point: https://www.youtube.com/watch?v=BLKHf40K0Wk
This program does exactly what you want. Implement secure voice in software. You would just have to transmit this over your cell phone. It’s possible this could be built out for Android for your specific use case, but right now it’s built for generalized radio transmission. So you could build two of these, for either party. And connect via audio call over the cell phone. You just might not get as much bandwidth, and call quality as you want. You’d have to keep reducing the settings until it worked
https://github.com/aarmono/crypto_transceiver_instructions
One big obstacle, is you’re going to have to do physical key exchange for your endpoints. If you use the internet for that key exchange, you might as well use encrypted voip.
OP doesn’t say where they are, but at least in the US, there is no more such a thing as the “cellular network” like the old circuit-based analog systems or 2G/3G, practically everything is VoIP now. All carriers are requiring VoLTE at a minimum which is IP-based (and so is everything that will come after it). So to me, using a different app like Signal is not going to be a huge difference in quality as long as the codec being used is a similar bitrate to what VoLTE uses (AMR-WB I think at a minimum).
Agreed. It’s a fun thought experiment. You have an acoustic tunnel. It may be transited over VoIP it may not. You can use that acoustic tunnel however you like, so implementing secure voice via audio is doable even if the underlying network turns it into VoIP
For what it’s worth signal voice quality is much much much much much much much higher, because it can use more bandwidth, then cellular voice connections