Make .ssh/authorized_keys file and add text ” ssh-rsa ” with spaces,
following the public key from the private key file on one line.
Assign rw permissions only for the owner.
$ chmod 600 ~/.ssh/authorized_keys.
Configure putty to use the private key when connecting (Connection -> SSH -> Auth).
More detailed instructions: http://www.tonido.com/blog/index.php/2009/02/20/ssh-without-password-using-putty/