“By default, SSH already uses a secure data communication between remote machines, but if you want to add some extra security layer to your SSH connections, you can add a Google Authenticator (two-factor authentication) module that allow you to enter a random one-time password (TOTP) verification code while connecting to SSH servers. You’ll have to enter the verification code from your smartphone or PC when you connect.
The Google Authenticator is an open-source module that includes implementations of one-time passcodes (TOTP) verification token developed by Google. It supports several mobile platforms, as well as PAM (Pluggable Authentication Module). These one-time passcodes are generated using open standards created by the OATH (Initiative for Open Authentication)…”