Control messages, discussed in detail earlier in Section 2.4>, instruct a Usenet server to take certain actions, like delete a message or create a newsgroup. If this facility is ``open to the public'', anyone with half a brain can forge control messages to create twenty new newsgroups, and then post thousands of articles into those groups. In the mid-nineties, we were hit by a storm of over 2,000 (two thousand) newgroup control messages, which rapidly taught us the danger of unprotected control messages and the protection against them.
The standard protection mechanism against this vulnerability is pgpverify, which can be downloaded from multiple Websites and FTP mirror sites by searching for pgpverify (the program) or pgpcontrol (the total software package). We have integrated this into our source distribution, so that our C-News works in a tightly coupled manner with pgpverify.
pgpverify works using public key cryptography, much like NoCeM, and all the official maintainers of respective Usenet group hierarchies sign control messages using their private keys. Your server will carry their public keys, and pgpverify will check the sign on each control message to ensure that it's from the official maintainer of the hierarchy. It will then act upon legit control messages and discard the spurious ones.
In today's nuisance-ridden Usenet environment, no sane Usenet server administrator receiving a feed of ``public'' hierarchies and control messages will even dream of running her server without pgpverify protection.