Guide: Approval Voting Distribution Subsystem

[rphmeier]

This subsystem is responsible for distributing assignments and approval votes generated by the Approval Voting Subsystem (#1601) to and from other validators.

These votes need to make their way to the provisioner, where they can be included on-chain. Gossip is suitable for this subsystem.

We might want this subsystem to be responsible for distributing disputes as well.

[burdges]

We need one politeness constraint that vote receivers know the candidate exists I suppose.

If we've no stronger politeness constraint then an adversary with 1/3rd would be validating all candidate, and thus know all candidates to be valid, and thus could vote valid from all their 1/3rd of validators, which technically means everyone verifying O(validators * candidates) = O(validators^2) signatures.

We could simply punt addressing this denial-of-service attack so long as these votes never go on chain, or at least not until an assignment goes on chain. If and when we want to address the off-chain attack we could create a politeness criteria for gossiping yes votes too, based upon assignments existing. We should bypass politeness for disputes though.