Managing SSH keys involves tasks such as adding removing unwanted keys, and securing keys to prevent unauthorized access.
1. Listing SSH Keys:
If you want to list the SSH keys present in the authorized_keys file on the server, you can do so using the following command:
cat ~/.ssh/authorized_keys
This command displays the contents of the authorized_keys file, showing the public keys that are authorized to access the server. Each line typically represents one authorized key.
If you have multiple users, you can also view the authorized_keys file for a specific user. For example:
cat /home/username/.ssh/authorized_keys
Replace username with the actual username for which you want to check the authorized_keys file.
Remember that the authorized_keys file contains the public keys of users who are allowed to log in using key-based authentication. Each public key should be on a separate line in the file.
2. Removing SSH Keys:
To remove an SSH key, you can manually edit the ~/.ssh/authorized_keys file on the server or use the ssh-keygen command:
ssh-keygen -R server_ip
This command removes all keys belonging to a specific server from the ~/.ssh/known_hosts file.
3. Securing SSH Keys:
Setting proper permissions:
Ensure that your SSH key files have the correct permissions. The private key should be readable and writable only by the owner:
chmod 600 ~/.ssh/authorized_keys
The ~/.ssh/ directory should be writable only by the owner:
chmod 700 ~/.ssh
Using SSH agent:
If you're using passphrase-protected keys, consider using an SSH agent to avoid entering the passphrase every time. Start the agent and add your key:
eval "$(ssh-agent -s)"
ssh-add ~/.ssh/id_rsa
Password-Protecting your private key:
You can add or change the passphrase for an existing private key:
ssh-keygen -p -f ~/.ssh/id_rsa
Follow the prompts to set a new passphrase.
4. Reviewing and monitoring SSH Logs:
Periodically review the SSH logs (/var/log/auth.log on Debian-based systems) to check for any unusual or unauthorized access attempts. Investigate and take appropriate actions if necessary.
5. Backup SSH Keys:
Regularly back up your SSH keys to prevent data loss. Copy the ~/.ssh/ directory to a secure location:
cp -r ~/.ssh /path/to/backup
By following these steps, you can effectively manage your SSH keys, remove unwanted keys, and take measures to secure your keys and the authentication process. Regularly reviewing and updating your key management practices contributes to a more secure SSH environment.