How to Generate A Public/Private SSH Key in Linux - Make Tech Easier

If you regularly use SSH to access a remote server, enhancing your SSH security can be achieved by setting up a public/private key pair. This method eliminates the need to send passwords over the network and helps protect against brute force attacks.

On Linux systems, generating an SSH key pair is straightforward.

1. Launch a terminal and enter:

<code>ssh-keygen -t rsa</code>

Alternatively, you can opt for DSA (Digital Signature Algorithm) instead:

<code>ssh-keygen -t dsa</code>

Note: There's ongoing discussion around the relative security of DSA versus RSA. Unless you're deeply invested in the cryptographic differences, either option works well for general use.

2. You'll be prompted to choose a location to save the key. By default, it’s stored in the .ssh directory within your home folder. Simply press Enter to use this default path.

3. Next, you’ll be asked to set a passphrase. This isn’t the password for the remote server—it’s a local passphrase to protect your private key. If someone gains access to your private key file, they’ll still need this passphrase to use it. Setting a passphrase is optional; press Enter to skip it.

4. The key generation process will now complete. Use your file manager to go to the .ssh directory. You should see two new files: id_rsa (your private key) and id_rsa.pub (your public key).

5. Transfer your public key to the remote server using this command:

<code>ssh-copy-id username@remote-host-ip-address</code>

6. Now, log into your remote server and open the SSH configuration file:

<code>ssh username@remote-host-ip-address&lt;br&gt;&lt;/br&gt;sudo nano /etc/ssh/sshd_config</code>

Locate the following lines in the file and ensure they are configured as shown:

<code>RSAAuthentication yes&lt;br&gt;&lt;/br&gt;PubkeyAuthentication yes &lt;br&gt;&lt;/br&gt;PasswordAuthentication no</code>

Save the file by pressing Ctrl + O, then exit with Ctrl + X.

7. Restart the SSH service on the remote machine to apply the changes:

<code>sudo systemctl restart ssh</code>

You're all set! You can now connect to your server securely using:

<code>ssh username@remote-host-ip-address</code>

Frequently Asked Questions

I transferred my SSH key but still get a “Permission Denied” error.

This is typically caused by incorrect permissions on the .ssh directory or authorized_keys file on the remote server. The SSH service requires strict permission settings.

Fix this by logging into your remote machine directly and running these commands:

<code>chmod 700 /home/$USER/.ssh &amp;&amp; chmod 600 /home/$USER/.ssh/authorized_keys</code>

Then restart the SSH service:

<code>sudo systemctl restart ssh</code>

Can I have multiple SSH keys for the same server?

Yes, you can. Just make sure each key has a unique name when generating it:

<code>ssh-keygen -f /home/$USER/.ssh/filename</code>

When connecting, specify the correct key:

<code>ssh -i /home/$USER/.ssh/filename [email protected]</code>

Can I add a new SSH key to a remote server while using an old key?

Yes. First, add your new key to the SSH agent:

<code>ssh-add</code>

Then, connect to your old machine using SSH agent forwarding:

<code>ssh -A old.machine.ip.address &amp;&amp; ssh-add -c</code>

Afterward, press Ctrl + D to disconnect from the old machine. You can now use both keys to access the remote server.

Image credit: Unsplash. All modifications and screenshots by Ramces Red.

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