Updated 0.3 specification

[rocodes]

• WIP towards update protocol specification from manuscript in progress #101

Update protocol specification to 0.3, to match what is currently being drafted:

• Updated keys list
• Updated message encryption
• Algorithms
• Protocol overview

[cfm]

Looks great for the purposes of #85! I've left comments inline as they came to me, but take 'em or leave 'em as you see fit between here and updating protocol.md.

[cfm]

I did a pass on the "Keys" section today per #101. I'm marking this as ready for review mostly to discuss with @rocodes next week whether to tackle the rest of #101 here or split it up for incremental review.

[cfm]

Moving this back to "in progress" because I suspect this is going to become the catchment pull request in which we accumulate the v0.3 specification for merge into main. :-)

[cfm]

Thanks, @rocodes! Based on our conversation today, here's a possible path to merging this into main as v0.3:

1. docs: reconcile key setup (including signatures) with schedule #110 is ready for review (now neutral documentation)
2. docs: reduce pseudocode to HPKE single-shot APIs #111 I'll finish tomorrow
3. Maybe we remove the overview sequence diagram for now?
4. The remaining tasks in update protocol specification from manuscript in progress #101 can be follow-up work...
5. ...along with incremental revisions as we consider them?

What do you think? I think (5) really captures my goal at this point: to be able to consider incremental revisions on this foundation.

[cfm]

As of today:

1. docs: reconcile key setup (including signatures) with schedule #110 is ready for review (now neutral documentation)
2. docs: reduce pseudocode to HPKE single-shot APIs #111 I'll finish tomorrow
3. Maybe we remove the overview sequence diagram for now?

@rocodes, feel free to tag me next week on anything we need to get this into main!

[rocodes]

I've added a couple of notes from the WIP 0.3 md doc to the protocol readme.md about future discussion areas, and I think everything else is captured in protocol.md, so I have deleted the 0.3-wip doc. I think this is ready for main, pending CI.

[rocodes]

(cherry-picked last commit from #112)

[cfm]

Huzzah. Thanks for tag-teaming on this, @rocodes!