How to authenticate using Public Key Authentication method in SSH

Authenticating with SSH using a private key is a secure method to access a remote server without the need for a password. This approach enhances security by relying on cryptographic keys, which are less vulnerable to brute-force attacks compared to passwords. To successfully authenticate using a private key, you need to ensure that your private key file is properly configured and has the correct permissions.

When you attempt to authenticate with an SSH server, the server checks if the private key corresponds to a public key stored on the server. If the key pair matches, access is granted. However, if the private key file is improperly secured, SSH will issue a warning and refuse to use the key, preventing authentication.

To authenticate with SSH using a private key, ensure your key file is secure and follow these steps to properly configure and use your private key for authentication.

1. Locate your private SSH key file on your system.
2. Ensure that your private key file has the correct permissions.

   $ ls -l .ssh/id_rsa
   -rw------- 1 user group 1700 May 12 2021 .ssh/id_rsa

   The file should be only readable and writable by the owner (permission 600).

3. Start a terminal session.
4. Connect to the remote server using the SSH command with the -i option to specify your private key.

   $ ssh -i .ssh/id_rsa user@remote-server.com

   Replace user@remote-server.com with your actual username and server address.

5. If the server recognizes your key and the permissions are correct, you will be authenticated and granted access to the server.
6. Ensure that the public key corresponding to your private key is added to the ~/.ssh/authorized_keys file on the server.