How to Disable Public Key Authentication in SSH

Secure Shell (SSH) is a widely used protocol for remote computer access over networks. Public key authentication is a method of authenticating users in SSH, where a private key is used to authenticate the user, and a public key is stored on the server. While public key authentication is a secure method of authentication, there are times when it may be necessary to disable it. This article will discuss how to disable public key authentication in SSH.

Why Disable Public Key Authentication?

Before we get started, let’s discuss why someone may want to disable public key authentication in SSH. There are a few reasons why this might be necessary:

1. Security concerns – While public key authentication is generally secure, there may be some situations where it is deemed too risky to use. For example, if there is a concern that someone could gain unauthorized access to a private key, it may be necessary to disable public key authentication.
2. Compatibility issues – Some legacy systems or applications may not support public key authentication, and disabling it may be necessary to allow access.
3. Testing purposes – In some cases, it may be necessary to disable public key authentication for testing or troubleshooting purposes.

Now that we understand why someone might want to disable public key authentication, let’s discuss how to do it.

Disabling Public Key Authentication in SSH

There are a few different ways to disable public key authentication in SSH, depending on your specific needs. We will cover the two most common methods below.

Method 1: Modify SSH Configuration

The first method involves modifying the SSH configuration file (/etc/ssh/sshd_config) on the server. This is the recommended method for permanently disabling public key authentication.

1. Open the SSH configuration file in a text editor with root privileges (e.g. sudo nano /etc/ssh/sshd_config).
2. Find the line that reads “PubkeyAuthentication yes” and change it to “PubkeyAuthentication no”.
3. Save the changes and exit the text editor.
4. Restart the SSH daemon with the command “sudo service ssh restart”.

sudo nano /etc/ssh/sshd_config

PubkeyAuthentication no

sudo service ssh restart

After completing these steps, public key authentication will be disabled on the server.

Method 2: Use SSH Command Line Option

The second method involves using a command line option to temporarily disable public key authentication for a single SSH session.

1. Open a terminal window and enter the following command:

ssh -o PubkeyAuthentication=no user@server 

2. Replace “user” with the username you want to log in as, and “server” with the IP address or hostname of the server.
3. Enter your password when prompted.

This will disable public key authentication for the current SSH session only.

Conclusion

This article discussed how to disable public key authentication in SSH. We covered the reasons why someone might want to do this, as well as the two most common methods for disabling it. If you don’t need to disable public key authentication for security concerns, compatibility issues, or testing purposes, following the steps outlined in this article will allow you to do so effectively. Remember always to consider the security implications of disabling public key authentication and only do so when necessary.

As a final note, it’s important to keep your SSH configuration secure and up-to-date. This includes regularly updating your SSH software and configuration, as well as following best practices for key management and access control. By staying vigilant and proactive, you can help ensure that your SSH connections remain secure and reliable.

📕 Related articles about Linux

• How to Show Failed SSH Login
• How to hide or unhide files and folders in Linux
• How to check disk size and usage in Linux
• How to force user to logout in Linux
• How to sniff network traffic in Linux
• What is Brute Force in Linux: Explained in Detail