Discourse Encrypt is a plugin that provides a secure communication channel through Discourse. Read more about the plugin on Meta...
Follow Install a Plugin
how-to from the official Discourse Meta, using git clone https://github.com/discourse/discourse-encrypt.git
as the plugin command.
Please note that WebCrypto API is restricted to secure origins, which basically means that you must enable HTTPS before using this plugin.