Prevent SSH Bruteforce and Hacks By Disabling Password Authentication
One simple way to keep your server public but almost impossible to hack via SSHis to disable password authentication over SSH. This means the only way in is via your own private key that only you should have.
Edit your /etc/ssh/sshd.conf file
Set this option
PasswordAuthentication no
Restart your SSH server.
service sshd restart
........
Disable SSH Password Authentication to Increase Security and Harden SSH Linux Unix Server Ubuntu Mint Centos Debian
Just a note before you do this you should have a sure, guaranteed way into the system such as local, KVMor preferably publickey making bruteforce SSH absolutely impossible since there is no password to bruteforce and even if someone knew the password they wouldn't be able to login except from the local console (presumably you should make sure no one unauthorized has physical access).
1. Edit /etc/ssh/sshd_config
Find the section like this:........