So this is a great thread. I have been thinking about this too.. and what if we are coming at it from the wrong direction? Identity being tied to a given URL has always been a pain point. If i get a new URL its almost as if i have a new identity because not only am I serving at a new location but all my previous communications are broken because the hashes are all wrong.
What if instead we used this idea of signatures to thread the URLs together into one identity? We keep the URL to Hash in place. Changing that now is basically a no go. But we can create a signature chain that can link identities together. So if i move to a new URL i update the chain hosted by my primary identity to include the new URL. If i have an archived feed that the old URL is now dead, we can point to where it is now hosted and use the current convention of hashing based on the first url:
The signature chain can also be used to rotate to new keys over time. Just sign in a new key or revoke an old one. The prior signatures remain valid within the scope of time the signatures were made and the keys were active.
The signature file can be hosted anywhere as long as it can be fetched by a reasonable protocol. So say we could use a webfinger that directs to the signature file? you have an identity like frank@beans.co that will discover a feed at some URL and a signature chain at another URL. Maybe even include the most recent signing key?
From there the client can auto discover old feeds to link them together into one complete timeline. And the signatures can validate that its all correct.
I like the idea of maybe putting the chain in the feed preamble and keeping the single self contained file.. but wonder if that would cause lots of clutter? The signature chain would be something like a log with what is changing (new key, revoke, add url) and a signature of the change + the previous signature.
# chain: ADDKEY kex14zwrx68cfkg28kjdstvcw4pslazwtgyeueqlg6z7y3f85h29crjsgfmu0w
# sig: BEGIN SALTPACK SIGNED MESSAGE. ...
# chain: ADDURL https://txt.sour.is/user/xuu
# sig: BEGIN SALTPACK SIGNED MESSAGE. ...
# chain: REVKEY kex14zwrx68cfkg28kjdstvcw4pslazwtgyeueqlg6z7y3f85h29crjsgfmu0w
# sig: ...