Using SSH Keys and Disabling Root Login

Why use SSH keys?

• SSH key pairs provide more secure authentication than passwords.

• Only the private key (kept on your computer) can unlock access, while the public key (stored on the server) verifies your identity.

• This prevents brute-force password attacks.

Setting up SSH keys

Generate a key pair on your computer:

ssh-keygen -t ed25519

(On Windows: ssh-keygen.exe)

Copy the public key to the server:

ssh-copy-id -i ~/.ssh/id_ed25519.pub user@server

If ssh-copy-id is unavailable, manually append the public key to ~/.ssh/authorized_keys on the server.

Test login:

ssh user@server

If successful, no password will be required.

Disabling password and root login

Once SSH key login is working, you can disable both password login and direct root login for better security.

Edit the SSH server configuration file:

sudo nano /etc/ssh/sshd_config

Enable public key authentication

PubkeyAuthentication yes

Disable password login and root login

PasswordAuthentication no
PermitRootLogin no

Save the file and restart the SSH service:

On RedHat/Fedora/CentOS

sudo systemctl restart sshd

On Debian/Ubuntu:

sudo systemctl restart ssh

(On older systems: sudo service ssh[d] restart)

Now your server will:

• Accept only SSH key authentication

• Block root login over SSH