How to use SSH keys with PuTTY

This article describes how to use PuTTY for passwordless SSH access via public/private key pairs.

• Open the PuTTYgen utility which comes along the PuTTY suite of programs:

• Click on Generate to start generating a public/private key pair
• You are asked to generate some randomness by moving the mouse on the area below the progress bar:

• When done the public key is shown and the Save buttons are enabled:

• Click on "Save private key":

• Enter a name and select a destination folder, then click "Save". IMPORTANT: This file MUST reside on your computer and it cannot leave it or be sent over any network.
• Do likewise for the public key (click on "Save public key").
• Now go back to the PuTTYgen main screen and select the public key with the mouse, right click on the selection and copy it.
• Open a new PuTTY session to the Linux machine you want to connect via those SSH keys.
• At prompt, cd to .ssh/ folder:

• With a text editor of your choice, open the authorized_keys file. If not existing, an empty one will be created:

• Go to the end of file and paste the public key as a new line (middle or right mouse buttons click when in text editing mode):

• Save, exit and close the PuTTY session. Now you need to tell PuTTY to use the new key pair.
• Go back to the PuTTY main window, load your saved session settings from the Session tab.
• Go to Connection -> SSH -> Auth and click on "Browse":

• Select the private key file you saved previously and click "OK".
• Go back to the Session screen, and save the new session settings for future use.
• You are done! Try to connect: you should go straight to the shell prompt with no password request.

Possible issues

If you are still prompted for a password, try the following:

• Make sure you did not miss any character in the copy/paste of the public key. If not sure, copy it again from the saved public key file and re-do the paste.
• Check the authorized_keys permissions if creating a new file. They must be 644 (see the chmod man page).
• Make sure your private key is loaded into the PuTTY session.

-- Federico Melaccio - 2014-07-11