centos 8 ssh key authentication

admin3 April 2024Last Update :

Unlocking the Power of SSH Key Authentication in CentOS 8

In the realm of server management and secure communications, SSH (Secure Shell) stands as a bastion of security and convenience. With CentOS 8, system administrators and developers alike can harness the full potential of SSH key authentication to establish secure connections without the repetitive need for passwords. This article delves into the intricacies of setting up and managing SSH key authentication on CentOS 8, providing a comprehensive guide that blends technical expertise with engaging insights.

Understanding SSH Key Authentication

SSH key authentication is a method used to securely access a remote server without the need for typing a password each time. It relies on a pair of cryptographic keys: a private key, which is kept secret by the user, and a public key, which can be shared openly. The elegance of this system lies in its simplicity and robustness; only someone with the correct private key can authenticate to the server configured with the corresponding public key.

The Benefits of SSH Key Authentication

  • Enhanced Security: SSH keys are nearly impossible to decipher through brute force attacks compared to traditional passwords.
  • Convenience: Once set up, users can access servers quickly without entering a password every time.
  • Automation Friendly: Scripts and automated processes can run smoothly without manual password intervention.

Setting Up SSH Key Authentication on CentOS 8

The journey to implementing SSH key authentication on your CentOS 8 system involves several steps, each crucial to ensuring a seamless and secure experience.

Step 1: Generating Your SSH Key Pair

Firstly, you’ll need to generate an SSH key pair on your local machine. Open your terminal and use the following command:

ssh-keygen -t rsa -b 4096

This command creates a new RSA key pair with a length of 4096 bits, offering strong security. You will be prompted to enter a file path to save the keys and an optional passphrase for added security.

Step 2: Copying the Public Key to Your CentOS 8 Server

With your key pair ready, the next step is to copy the public key to your CentOS 8 server. The ssh-copy-id utility simplifies this process:

ssh-copy-id user@your_centos8_server

Replace “user” with your actual username and “your_centos8_server” with the server’s IP address or hostname. If you’ve set a passphrase, you’ll be asked to enter it.

Step 3: Configuring SSH Daemon Settings

To enforce key authentication, modify the SSH daemon configuration on your CentOS 8 server. Edit the /etc/ssh/sshd_config file and ensure these settings are in place:

PubkeyAuthentication yes
PasswordAuthentication no
ChallengeResponseAuthentication no
UsePAM no

After making changes, restart the SSH service to apply them:

systemctl restart sshd

Step 4: Testing SSH Key Authentication

It’s crucial to test your setup before logging out of the server to avoid lockouts. Open a new terminal window and attempt to SSH into your CentOS 8 server:

ssh user@your_centos8_server

If everything is configured correctly, you should gain access without being prompted for a password.

Best Practices for Managing SSH Keys

Proper management of SSH keys is vital for maintaining a secure environment. Here are some best practices to follow:

  • Regularly Rotate Keys: Change your SSH keys periodically to mitigate the risk of compromised keys going unnoticed.
  • Use Passphrases: Adding a passphrase to your private key provides an extra layer of security, especially if the key is stolen.
  • Limit Access: Only copy your public key to servers where necessary and regularly audit which machines have your key installed.
  • Monitor Sessions: Keep an eye on active SSH sessions and investigate any unfamiliar connections.

Advanced Configuration and Troubleshooting

While the basic setup of SSH key authentication is straightforward, there may be times when advanced configuration or troubleshooting is required.

Using Multiple SSH Keys

For those managing multiple servers or services, using different SSH keys for each context can enhance security. When generating a new key pair, specify a unique filename:

ssh-keygen -t rsa -b 4096 -f ~/.ssh/id_rsa_custom

Then, use the -i option with SSH to specify which private key to use for a connection:

ssh -i ~/.ssh/id_rsa_custom user@your_centos8_server

Troubleshooting Common Issues

If you encounter issues with SSH key authentication, check the following:

  • The permissions of your ~/.ssh directory and files should be restrictive (e.g., 700 for the directory and 600 for files).
  • Ensure the SSH daemon is running and listening on the correct port.
  • Verify that the public key is correctly installed in the ~/.ssh/authorized_keys file on the server.
  • Check the SSH daemon logs for any error messages that can provide clues.

Frequently Asked Questions

Can I still use password authentication after setting up SSH key authentication?

Yes, but it’s not recommended for security reasons. If you must enable password authentication, change PasswordAuthentication to “yes” in the /etc/ssh/sshd_config file and restart the SSH service.

What should I do if I lose my private key?

If you lose your private key, you’ll need to generate a new key pair and install the new public key on your server. Ensure you remove the old public key from the ~/.ssh/authorized_keys file to prevent unauthorized access if the lost key is found by someone else.

How can I revoke access for a specific key?

To revoke access for a specific key, simply remove the corresponding public key line from the ~/.ssh/authorized_keys file on the server.


SSH key authentication offers a secure and efficient way to manage server access. By following the steps outlined in this article, you can set up a robust authentication mechanism on your CentOS 8 system that enhances security while streamlining your workflow. Remember to adhere to best practices for key management and stay vigilant against potential security threats.


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