How to use public key authentication method in PuTTY

Using public key authentication in PuTTY provides a secure method for connecting to a remote OpenSSH server. This approach uses a public key on the server and a matching private key on the local client. PuTTY requires the key in ppk format to ensure compatibility with its authentication mechanism.

Generating or converting an existing OpenSSH key into a ppk format is crucial before attempting a key-based connection. Tools like PuTTYgen transform traditional OpenSSH keys into ppk format, allowing PuTTY to authenticate without relying on passwords.

Many organizations benefit from the robust nature of public key authentication, which reduces the need for password prompts and lowers the risk of brute force attacks. The protected, encrypted keys mitigate potential unauthorized access and help maintain data integrity.

1. Create a public and private key pair if you don't already have one.

   Related: How to generate SSH key pair on Windows

2. Copy your public key to server's authorized_keys file.

   Related: How to extract public key from SSH private key in Windows
   Related: How to copy an SSH public key to a server

3. Launch PuTTY.
4. Enter connection details such as Host Name / IP address and port.
5. Navigate to Connection → SSH → Auth from the sidebar menu.
6. Click on the Browse button to look for your PuTTY Private Key.

   Related: How to convert OpenSSH private key to PuTTY's .ppk

7. Select your PuTTY Private Key from the stored location and click on the Open button.
8. Click on the Open button to start the connection.
9. Click Yes if a security alert pops up as this is your first connection to the server and the server's key fingerprint is not in your PuTTY's cache.

   Related: How to edit known hosts key fingerprint for PuTTY

10. Enter the username that you want to connect as and press enter.
11. Enter the passphrase for the key if a passphrase protects your key.
12. You should be able to log in without providing your password to the system.