SERVER SIDE

1. disable SSH password authentication
   When you've decided to connect to your server via SSH key rather than the password, you would need to disable password authentication to require all users connecting via SSH to use key authentication. Next, you’ll disable root login to prevent the root user from logging in via SSH. These steps are optional but are strongly recommended.
   Here’s how to disable SSH password authentication and root login:
   Open the SSH configuration file for editing by entering the following command:

sudo nano /etc/ssh/sshd_config

Change the PasswordAuthentication setting to no as shown below. Verify that the line is uncommented by removing the # in front of the line if there is one:

PasswordAuthentication no

Change the PermitRootLogin setting to no as shown below:

PermitRootLogin no

Save the changes to the SSH configuration file by pressing Control-X, and then Y.
Restart the SSH service to load the new configuration. Enter the following command:

sudo systemctl restart sshd

After the SSH service restarts, the SSH configuration changes will be applied.