SimpleSecure is a plugin that allows you to insert a secure contact form on any page or post. The email message submitted by your visitor is securely encrypted using GPG/PGP, however no binaries are required nor are any shell calls necessary. SimpleSecure includes a pure PHP port of the GPG encryption functions which allows it to run on any server that supports PHP. In other words, you do not need to install GPG or allow shell access to PHP on your server.
via WordPress › SimpleSecure « WordPress Plugins.