How to use public key authentication in PuTTY

One of the option to connecting to an SSH server is via the Public Key Authentication method. For this you need to have a public and private key pair and for your public key to be available in the server's authorized_keys file.

If you're on Windows then you're likely to connect to a remote SSH server using PuTTY and as such you'll need a PuTTY Private Key (ppk) file and the associated public key which you can generate using PuTTY Key Generator (PuTTYGen).

1. Create a public and private key pair if you dont 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 generate SSH public key from private key in Windows
   Related: How to add SSH key to 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 your key is protected by a passphrase.
12. You should be able to log in without providing your password to the system.