How to use public key authentication in PuTTY

Public Key Authentication in PuTTY allows you to securely connect to an OpenSSH server. This method uses a public key stored on the server and a corresponding private key on the client machine. PuTTY requires the private key to be in the PuTTY Private Key (ppk) format.

To use public key authentication, you must first ensure your keys are correctly generated and configured. If you have an existing OpenSSH private key, convert it to ppk format. PuTTY then uses this ppk file to authenticate the connection without needing a password.

This step-by-step guide explains how to set up and use public key authentication with PuTTY.

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.