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?
non voip
I think this is not doable. You don’t have access to the voice codec to start with, and the phone at the other end generally won’t receive the bit stream coming out of it anyway. With a non-rooted phone it’s hard to even get to the voice stream. You might be able to send subliminal encrypted text messages through a voice channel and that could be kind of cool, and hard to detect. That idea has been around for a while but I don’t know of existing software that does it.
With VOIP, of course there are many encrypted systems available.
Added: also I assumed throughout that you meant present day mobile phones. With land phones at both ends, it may still be doable using dialup modems, but that was a 1990s thing and was pretty awful when you got down to it. It existed though.
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.
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.
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.
You can try Wire (https://wire.com/en)
I know Wire, but I asked for non voip solutions.
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there are some obscure hardware options for this but hardware based audio encryption is mostly just enterprise stuff, it’s very difficult for a consumer to obtain
Isnt enough software encryption like with voip calls (like telegram)?
It’s on a different stack. Telegram (and VoIP) operates on the network stack, cellular call is working on the GSM/LTE stack. Networkin stack is more opened and free to do what you want; GSM/LTE stack have many proprietary tech that’s is not open to everyone.
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.
