1482
Welp that answers a lot of why all .ml are down
(i.imgur.com)
This is a most excellent place for technology news and articles.
Activitypub signatures that each user and group sends out their messages with.
It's not an assumption, it's how activitypub works.
https://www.w3.org/wiki/SocialCG/ActivityPub/Authentication_Authorization
I assumed that once federated the public key would be remembered and signatures that do not match it would be handled, but you may be correct. I do wonder whether this could be a problem as instances close down over time. I'll have to spend some more time researching to see if there's a more clear answer, or if any ActivityPub implementations have their own way of handling that situation.