this post was submitted on 21 Jul 2023
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No, the signatures wouldn't match.
That's an assumption that lemmy will quit federating with a server that does not match.
And what signature are we talking about anyway? Is not certificates...
Activitypub signatures that each user and group sends out their messages with.
It's not an assumption, it's how activitypub works.
Can you show me documentation that shows communities or servers are signed?
https://www.w3.org/wiki/SocialCG/ActivityPub/Authentication_Authorization
So looking at that spec... Nothing there is validation that current messages originate from an "original" server...
I don't think either of these signature options for Server to Server communications means that my current lemmy.saik0.com instance can't be torn down (delete LXC container) and reconfigured as a brand new instance (New LXC container) and other instances wouldn't know that there's been a change to the instance running here... or more accurately would flag a change. I think these signatures are all about not being able to spoof OTHER instances. eg, lemmy.ml can't send messages on behalf of lemmy.world.
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.
Yeah that's my worry. I'm pretty sure(and could be wrong) that message/ keys are only checked on ingestion. So i would get key value for a message coming in and can check that is currently valid, not that it's "changed" since 2 months back. I think this could allow for some one to ressurrect an old Lemmy service and masquerade as the old one... communities , users... all of it.