Use PuTTYgen to generate public and private keys. Paste the public key into /home/userid/.ssh/authorized_keys. Select Connection/SSH/Auth in PuTTY for each host entry to identify the private key. Retrieve the public key with the private key by clicking the ‘Load’ button in PuTTYgen. If you use a passphrase for added security, you must use it each time you log into a server. Here’s a place to start.