BEEFY: gossip finality proofs #13727
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acatangiu
added
A0-please_review
Gossip finality proof in _both_ cases of reaching finality threshold through votes: 1. threshold reached through self vote, 2. threshold reached through incoming vote.
| justif = gossip_proofs.next() => { | ||
| if let Some(justif) = justif { | ||
| // Gossiped justifications have already been verified by `GossipValidator`. | ||
| if let Err(err) = self.triage_incoming_justif(justif) { |
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Just checking - the justification is verified by GossipValidator and we know it is valid. But equivocations are detected here, by BeefyWorker. And unless I'm missing something, they're only detected when we handle incoming votes. I wonder if it is possible for validator to make two votes and stay unnoticed because the second vote will be gossiped using finality proof? I believe that even if I'm right in my assumption, it is very unlikely scenario (given enough validators set length), so maybe something for the future
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yes, for a validator set of size N, it's possible now for m voters to "undetectably equivocate" by sending a vote for mmr_root_2, then including another vote for mmr_root_1 in a proof alongside 2*N/3 other votes for mmr_root_1.
- Because the precondition of required
2*N/3"good" votes before being able to "undetectably equivocate", it meansmcan be at mostN/3in "perfect" network conditions where coordination of who sees what gossipped votes is 100% controlled by dishonest validators. - Even in these perfect conditions where
m=N/3, best you could do is partition the network to getN/3honest voting onmmr_root_1, anotherN/3honest voting onmmr_root_2andN/3dishonest equivocating both => at least one validator will have to visibly equivocate to get over threshold.
Also, because BEEFY is based on GRANDPA, finality point.2 above is not possible, honest validators cannot be convinced to vote on anything other than what GRANDPA finalized.
Ergo, I believe this is not a problem/risk.
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@serban300, I've addressed all comments |
* sc-consensus-beefy: add justifications to gossip protocol * sc-consensus-beefy: voter gossips finality proofs * sc-consensus-beefy: add finality proof gossip test * sc-consensus-beefy: always gossip finality proof Gossip finality proof in _both_ cases of reaching finality threshold through votes: 1. threshold reached through self vote, 2. threshold reached through incoming vote. * address comments
* sc-consensus-beefy: add justifications to gossip protocol * sc-consensus-beefy: voter gossips finality proofs * sc-consensus-beefy: add finality proof gossip test * sc-consensus-beefy: always gossip finality proof Gossip finality proof in _both_ cases of reaching finality threshold through votes: 1. threshold reached through self vote, 2. threshold reached through incoming vote. * address comments
* sc-consensus-beefy: add justifications to gossip protocol * sc-consensus-beefy: voter gossips finality proofs * sc-consensus-beefy: add finality proof gossip test * sc-consensus-beefy: always gossip finality proof Gossip finality proof in _both_ cases of reaching finality threshold through votes: 1. threshold reached through self vote, 2. threshold reached through incoming vote. * address comments
Adds gossiping BEEFY finality proofs to the BEEFY gossip protocol.
round_num >= current_best_beefy,thresholdvalidator signatures.Fixes #13733