2010/01/12

Fork in the Road for Salmon


Happy New Year!

Over the past several weeks, I've been doing a Salmon conference roadshow, talking and listening to people about the protocol and getting feedback.

At IIW, we had a "Magic Security Pixie Dust" Salmon session which kicked around the use cases and challenges in detail.  There and elsewhere I got basically two kinds of feedback:  (a) The specification, especially the signatures, was too complicated; and (b) the specification, especially the signatures, was not comprehensive enough.

There was a suggestion to drop signatures entirely and just rely on reputation of the salmon generators, who would be on the hook for vouching for the identity of their users.  This would simplify the protocol but at the cost of giving it effectively the same security characteristics as email.  This was initially attractive and I spent some time playing with what that would look like.  Unfortunately, I am pretty sure that it would just make operation more complex and adoption more problematic, and you'd likely need to pre-federate every salmon generator/acceptor pair to get things off the ground.  

At another meeting I was fortunate enough to get Ben Laurie in the room, and he suggested a simple mechanism for comprehensive signatures.  I've been playing with it and it's looking pretty good.  By that I mean that it works, and I think it's implementable even with stone knives and bearskins minimal library support.

And, in parallel, many people have started talking about additional use cases for Salmon, most of which benefit from a simple signing mechanism:
  • A personal store of comments, posts, and activities you do around the Web, kept in your online storage mechanism of choice, used for backup, archiving, and search purposes ("what was that conversation I had last week?...")
  • Salmon for mentions (@replies to a particular person) which just send a Salmon, not necessarily as a reply to a piece of content, but to a person as a mentionee.
  • Structured data with verifiable provenance for things like bids and asks
  • Building up and using distributed reputation based on analysis of comments, ratings, reviews, etc. published via Salmon.
  • ...etc
Sometimes, the more general problem is easier to solve.  After a lot of thinking, talking, and coding, I've come around to believing in the more comprehensive solution.

This doesn't change the outline of Salmon specified at http://salmon-protocol.org.  It drops the sign-selected-fields mechanism, and lets you sign the entire Salmon, including any extension data.  As an added bonus, it doesn't matter what format you choose, what your character encoding or Infoset serialization is; it'll just work regardless.  

Since it is a public key signature mechanism, it does require a public key infrastructure.  Fortunately, we have the pieces to build one easily and simply at hand.

I'll blog first about the signature mechanism, and second about the public key mechanism, in the next couple of days.