This is what I am trying to do:
local web local Recipient <--- local tunnel host server <--- Sender server1 ngrok or other device1
My goal is to securely transmit a string from
server1 is not accessible from the internet, thus starting a tunnel via
ngrok or similar. However, I do not want to/can trust the tunnel server in the middle. If I understand correctly, the tunnel server could become compromised (as in MITM listening to the tcp socket/proxy).
What options do I have to securely transmit data from let's say a mobile phone to an app running behind a firewall if you can't trust the infrastructure in the middle?
I am researching https://signal.org/docs/ right now, but don't quite understand how it could work in a local tunnel context.
EDIT: Asymmetric keys seems to be what I am looking for.