And once we have that worked out in software using simple off the shelf stuff on hand and the simplest protocols possible, then can we do usb dongles so we can be really really really sure the private keys stay safe? Hint: There's a product that can be made and sold by sites as an additional stream to help fund public portals to the signed-fediverse.
Dongle should have a physical switch that has to be turned on to flash a set of key-pairs to it and then when turned back appears as a USB device that can be sent text (which could include hashes and checksums for non-text content) and an EOF character and should return a set of signatures using all of the private keys on it (software ignores all but the one we care about).
Maybe no switch, just an SD slot but no USB storage interface or anything presented to the computer, the SD has to be written with the private keys and then inserted but is then safe from being read by anything but the dongle.
Maybe add a touchscreen to require entering a pin/password after inserting the dongle into your computer, but it doesn't really need that.
Okay.. Long rant for the evening finished. Slop Bad, Key-Pairs are a good way of identifying folks, phone numbers and email service providers aren't so much so anymore I'm thinking. And bots can't come to key-signing parties at the local coffee house.
Plus - key-signing parties at the local coffee house sounds nice, actually meeting people in the real world to prove you're human also means... actually... meeting people... in the real world... I kinda remember that, I think?