On the Subject of Feed Identities; I propose the following:

1. Generate a Private/Public ED25519 key pair
   
2. Use this key pair to sign your Twtxt feed
   
3. Use it as your feed’s identity in place of # url = as # key = ...
   

For example:

$ ssh-keygen -f prologic@twtxt.net
$ ssh-keygen -Y sign -n prologic@twtxt.net -f prologic@twtxt.net twtxt.txt

And your feed would looke like:

# nick        = prologic
# key         = SHA256:23OiSfuPC4zT0lVh1Y+XKh+KjP59brhZfxFHIYZkbZs
# sig         = twtxt.txt.sig
# prev        = j6bmlgq twtxt.txt/1
# avatar      = https://twtxt.net/user/prologic/avatar#gdoicerjkh3nynyxnxawwwkearr4qllkoevtwb3req4hojx5z43q
# description = "Problems are Solved by Method" 🇦🇺👨‍💻👨‍🦯🏹♔ 🏓⚯ 👨‍👩‍👧‍👧🛥 -- James Mills (operator of twtxt.net / creator of Yarn.social 🧶)

2024-06-14T18:22:17Z	(#nef6byq) @<bender https://twtxt.net/user/bender/twtxt.txt>  Hehe thanks! 😅 Still gotta sort out some other bugs, but that's tomorrows job 🤞
...

Twt Hash extension would change of course to use a feed’s ED25519 public key fingerprint.

@prologic@twtxt.net Some criticisms and a possible alternative direction:

1. Key rotation. I’m not a security person, but my understanding is that it’s good to be able to give keys an expiry date and replace them with new ones periodically.

2. It makes maintaining a feed more complicated. Now instead of just needing to put a file on a web server (and scan the logs for user agents) I also need to do this. What brought me to twtxt was its radical simplicity.

Instead, maybe we should think about a way to allow old urls to be rotated out? Like, my metadata could somehow say that X used to be my primary URL, but going forward from date D onward my primary url is Y. (Or, if you really want to use public key cryptography, maybe something similar could be used for key rotation there.)

It’s nice that your scheme would add a way to verify the twts you download, but https is supposed to do that anyway. If you don’t trust https to do that (maybe you don’t like relying on root CAs?) then maybe your preferred solution should be reflected by your primary feed url. E.g. if you prefer the security offered by IPFS, then maybe an IPNS url would do the trick. The fact that feed locations are URLs gives some flexibility. (But then rotation is still an issue, if I understand ipns right.)

In fact, maybe your public key idea is compatible with my last point. Just come up with a url scheme that means “this feed’s primary URL is actually a public key”, and then feed authors can optionally switch to that.

My first thought when reading this was to go to my typical response and suggest we use Nostr instead of introducing cryptography to Twtxt. The more I thought about it, however, the more it made sense.

1. It solves the problem elegantly, because the feed can move anywhere and the twt hashes will remain the same.
   
2. It provides proof that a post is made by the same entity as another post.
   
3. It doesn’t break existing clients.
   
4. Everyone already has SSH on their machine, so anyone creating feeds manually could adopt this easily.
   

There are a couple of elephants in the room that we ought to talk about.

1. Are SSH signatures standardized and are there robust software libraries that can handle them? We’ll need a library in at least Python and Go to provide verified feed support with the currently used clients.
   
2. If we all implemented this, every twt hash would suddenly change and every conversation thread we’ve ever had would at least lose its opening post.

@mckinley@twtxt.net To answer some of your questions:

Are SSH signatures standardized and are there robust software libraries that can handle them? We’ll need a library in at least Python and Go to provide verified feed support with the currently used clients.

We already have this. Ed25519 libraries exist for all major languages. Aside from using ssh-keygen -Y sign and ssh-keygen -Y verify, you can also use the salty CLI itself (https://git.mills.io/prologic/salty), and I’m sure there are other command-line tools that could be used too.

If we all implemented this, every twt hash would suddenly change and every conversation thread we’ve ever had would at least lose its opening post.

Yes. This would happen, so we’d have to make a decision around this, either a) a cut-off point or b) some way to progressively transition.

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: ...