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.
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.
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.
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.
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I know Wire, but I asked for non voip solutions.
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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?
Yeah third party apps can do end to end encryption. It uses the data network and not the cellular network then though.
Google Fi on Android actually does run E2E on calls https://fi.google.com/about/end-to-end-encrypted-calls/
With audio encryption hardware, sure. Speak into that and feed its output to the mic on the phone
do you know of any purchasable equipment? I’ve never been able to find any, then again I’m not versed in such things too much
I don’t myself. So I am not sure.
