You would need to have a) a private key for moodle accessible by the webservers and b) public keys for all your users.
This doesn't seem the sort of thing in a typical moodle scenario and seems of little benefit to me.
Do you have a use case in mind and would it be better served by a different tool?
Security and privacy
using gnupg when sending emails
This discussion has been locked because a year has elapsed since the last post. Please start a new discussion topic.