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?
Signal is a great example of this but I don’t think you’ll find any ways to do it non-VoIP.
https://en.wikipedia.org/wiki/Acoustic_coupler
Slap your phone in one of those bad boys and go to town with your TST 3550 or whatever.
As for cell phones, I don’t think it’s really supported. I’d recommend using a separate encrypted calling app, or getting a dedicated encrypted phone device.
Instead of fiddling with the limitation on Android set by Google, I think a custom crypto DAC/ADC would be far eaiser, though you need both hard and software knowledge to accomplish this. It also came with the added benefit of not processing cryptographic operations on a black box.
Still, I don’t know what goal you want to achieve and threat model is. If you are just curious if this possible, the answer will be ye with tons of hops amd hacks. If you really want security, I will advise you go another route.
Just curious really, would be cool using cellular network with an encrypted signal. Here some telcom companies offers infinite calls minutes but limited GBs of internet, so making voip calls would use those GBs.
My understanding of the way a phone call works leads me to believe the data would not survive the dynamic compression done at the various transmission points like towers, relays, or the occasional satellite. If neither party is moving and the towers in use do not change in load, it might be possible, but at that point you’re more tethered down than if you used a VPN.
This should be possible to do it software, but I don’t know about any apps or something else that deals with this. You would probably also need a rooted phone for it to work.
Why should I need a rooted phone? Can’t dialer apps send whatever they want through cellular network?
Yes and no. Google put some limitation on the software side. For example, you can’t do call record unless you’re in a country isn’t two party consent.
Maybe I’m wrong, but I think it’s not the dialer app that operates the microphone, or at least it does not have total control over it, to record something and pass something else to the system.
Not that I’m aware of phone calls traversed the cellular network and are uncrypted. Okay, well that’s not exactly true. They are encrypted, but the cellular network has the decryption key. That way nobody on the air can listen to the call, but the cell company can record it.
Can’t the signal be encrypted first by client and then sent to cellular network?
With audio encryption hardware, sure. Speak into that and feed its output to the mic on the phone
I think they are interested in a purely software solution
I think you’re right. I know for a fact that I do not know of any, not for regular phone calls. Obviously if you want to use the internet and data, there’s tons of options.