CPG has two branchs: The first one must be installed on an email server. Log-in process of this branch uses /etc/passwd. Hence, just real users of the email server can use CPG.
The second branch can be installed on any web server that does not need to be an email server. Log-in process of this branch uses MySQL database. Hence anyone can be a user of CPG with any name or any email address.
It is currently for Linux, Apache webserver and gnupg-1.0.6-5 only.
The link for this article located at CPG is no longer available.