(My comment, reposted here.) I recall a discussion on this topic a long time ago when I had a casual interest in anti-spam techniques. The idea was that someo

(My comment, reposted here.) I recall a discussion on this topic a long time ago when I had a casual interest in anti-spam techniques. The idea was that someone (JD) maintained a list of bad IP addresses. However, JD realised that some people might not want JD to maintain and publish his list, and would various means to stop him. (Lawsuits, DoS attacks, personal threats, etc.) So instead, he would anonymously publish updates to his list as signed Usenet messages. The idea was that even though he was anonymous, he would build up a reputation for quality over time and spammers couldn't pollute his list by posting fake updates because those fake updates would fail the signature check. The objection to this scheme was the man-in-the-middle problem. Under this plan, JD's first message to the world would be a unsigned PGP key over the same fakeable Usenet channel. What if, a spammer managed to capture all of JD's posts, including the initial key, and craft his own fake posts with the spammer's IP missing? (In the real world Usenet, this attack would be a rather impractical, but that's beside the point. Just acknowledging the fact.)