termux-reverse-ssh (trs)
Make Android phone accessible from a public server via reverse SSH tunnel. Root NOT needed.
Requirements & Function
You need a server accessible via SSH in public network, and an URL you can control to be valid or invalid.
trs will check whether a URL is accessible every 30 minutes. The URL is normally invalid and if it becomes valid, trs will be triggered and open a reverse SSH tunnel to a remote server, from which the phone's Termux SSH can be accessed aka phone can be remote controlled.
Installation
Install Termux and Termux:Boot. Launch Termux:Boot once.
Setup ssh and sshd in Termux. Then run install.sh in Termux. You'll be prompted for server and trigger URL information.
If everything works fine, trs will auto-launch on device startup.
Example usage
After your phone is stole... And if it isn't turned off...
Prepare the trigger URL
(Here it's by creating a file on an FTP/HTTP site -- a 404 URL becomes valid)
Reverse SSH tunnel will start after at most 30min
(It's a debugging picture, you won't see this, of course)
Connect to the server and access the phone, now in Termux: where there is a shell, there is a way
Photos being backed-up via scp: speed is not bad!
Others
NO WARRANTY
Read the source code for detailed usage. It's shorter than this README.
Security is not guaranteed. SSH private key is on phone.
I don't want to be "logged-in" to the server all the time, so didn't make an always-alive connection.
You shouldn't rely this on data protection. Backup regularly instead.