Generate key with putty key generator





Save the private key



Saving with or whitout Key passphrase



copy the public key from the screen




Make sure there is a .ssh folder in the user/home directory
change to home directory user
cd .ssh
ls


edit the authorized_keys file and paste the public key and save the file
sudo vim authorized_keys



edit the /etc/ssh/sshd_config file
sudo vim /etc/ssh/sshd_config file


Remove the # from
PubkeyAuthentication yes
AuthorizedKeysFile      .ssh/authorized_keys .ssh/authorized_keys2

 #PasswordAuthentication yes
and change yes to no
service sshd restart

Add server to Putty 

Start Putty and add the conection settings





Go to connection - SSH - Auth - Credentials and add the private ppk file with browse



Select Session and save the configuration



Click on open to start the session with out password