How to Enable SSH Public Key Authentication October 16, 2023

SSH public key authentication allows you to securely log in to a remote server without using a password. It is more secure than password-based authentication and is widely recommended for server access.

Follow the steps:

1. On the source server, navigate to the /etc/ssh directory, which contains the SSH configuration files. There are different types of SSH keys based on their encryption algorithms (DSA, RSA, ECDSA, Ed25519).
   In this example, RSA-encrypted keys are used.
   If no SSH keys are available, they can be created using the ssh-keygen command.
   For example:

   ssh-keygen -t rsa -b 4096

   This command will generate a public key at:

   /root/.ssh/id_rsa.pub

2. Copy the Public Key to the Destination Server
   Copy the contents of the public key file from the source server:

   /root/.ssh/id_rsa.pub

   Paste it into the following file on the destination server:

   /root/.ssh/authorized_keys

3. Verify Ownership and Permissions (Very Important)
   Set the correct permissions using the following command:
   

   chmod 700 ~/.ssh && chmod 600 ~/.ssh/authorized_keys

   If the root user is used to log in via SSH (root@ipAddress), ensure that the authorized_keys file is owned by root and located under /root/.ssh.

4. Update SSH Configuration
   On the destination server, ensure that the following entries are present in the SSH configuration file:

   vi /etc/ssh/sshd_config
   PermitRootLogin yes
   RSAAuthentication yes
   PubkeyAuthentication yes
   PasswordAuthentication no
   AuthorizedKeysFile .ssh/authorized_keys

5. Restart the SSH service using:

   systemctl restart sshd

6. Test SSH Login
   You can now log in to the remote server from the source host using:

   ssh root@remoteIPAddress

By following the above steps, you can enable SSH public key authentication for secure, password-less server access. This helps improve security and prevents unauthorised logins.