WP Encrypt is an easy-to-use client for the new Let’s Encrypt service which provides free SSL certificates for everyone. No reason to have an unprotected WordPress site any longer! 
Using the plugin, you can quickly acquire a new certificate for your site. Once you have registered and received a certificate, you can switch your site to HTTPS. 
The Let’s Encrypt service only provides certificates that are valid for 90 days. However, you can always renew them – no limitations there. And with this plugin you don’t even need to worry about that, the plugin will automatically renew existing certificates before they expire (as long as you want it to).
The plugin is fully compatible with Multisite and Multinetwork. In a Multisite it will take care of generating the certificate for all sites in the network. In a Multinetwork you will additionally have the option to generate the certificate for all sites in all networks. 
This plugin requires you to run at least PHP 5.3 on your server. You also need to have the
OpenSSL extensions active. Please check with your hosting provider if you’re not sure whether your server meets these requirements or how to set them up. You also need to be able to adjust the server configuration to use the certificate the plugin obtains.
If you don’t have permissions to modify the server configuration, you might be able to still use the certificates if your host provides an interface to upload your own SSL certificates. In that case you can simply upload the generated certificate files there.
 Almost no reason. You still need to be able to access and modify your server configuration to set up SSL and use the certificate the plugin obtained for you.
 The plugin does not automatically change your site to HTTPS. It obtains and the SSL certificate, but you still need to adjust your server configuration and change your site’s URL setting to use HTTPS. As a guide, you can follow this WP Beginner tutorial for example.
 The plugin currently generates the certificate for the entire setup in one step. Therefore it is most likely to fail on large setups with a huge amount of sites. This is the first thing on the list to be improved in a later version though.