You don't need encryption for paypal to work, it's perfectly safe without encryption.

/etc/ssh is not the right place for this web-app, as the keys need to be readable by the php web process. You could put them in the folder just above your public_html folder.

Setting up encryption for paypal is quite some work and not needed to protect the sensitive information against third parties, as that is already done by paypal. So you can perfectly not set it up. The only information that will be visible to the person that wants to pay is your paypal email address, which they will see anyway in their paypal confirmation email after payment.

Added instructions clarification as task #4399.