From 2872df663470096980cb074a8f8a276ba1058d2a Mon Sep 17 00:00:00 2001
From: Zaki Manian <zaki@manian.org>
Date: Sat, 6 Jul 2019 20:21:23 -0700
Subject: [PATCH] Remove verify future commit as uncessessary

---
 types/validator_set.go | 84 ------------------------------------------
 1 file changed, 84 deletions(-)

diff --git a/types/validator_set.go b/types/validator_set.go
index 11c722c9b..12f849a67 100644
--- a/types/validator_set.go
+++ b/types/validator_set.go
@@ -638,90 +638,6 @@ func (vals *ValidatorSet) VerifyCommit(chainID string, blockID BlockID, height i
 	return errTooMuchChange{talliedVotingPower, vals.TotalVotingPower()*2/3 + 1}
 }
 
-// VerifyFutureCommit checks to see if a given future validator set has
-// committed a block, and whether those who signed of this future validator set
-// has sufficient overlap with this validator set.
-//
-// vals is the current validator set that we know.  Over 2/3 of the power in
-// this valset is expected to have signed this block.
-//
-// Justification for the 2/3: In Tendermint, 1/3 of the voting power can halt
-// or fork the chain, but 1/3 can't make arbitrary state transitions.  You
-// still need > 2/3 Byzantine to make arbitrary state transitions.
-//
-// To preserve this property in the light client, we also require > 2/3 of the
-// old vals to sign the future commit at H, that way we preserve the property
-// that if they weren't being truthful about the validator set at H (block hash
-// -> vals hash) or about the app state (block hash -> app hash) we can slash
-// > 2/3.  Otherwise, the lite client isn't providing the same security
-// guarantees.
-//
-// newVals is the validator set that signed this block.  Only votes from new are
-// sufficient for 2/3 majority in the new set as well, for it to be a valid
-// commit.
-//
-// NOTE: This doesn't check whether the commit is actually a future commit,
-// because the current height isn't part of the ValidatorSet.  Caller must
-// check that the commit height is greater than the height for this validator
-// set.
-//
-// NOTE: This function is strictly more restrictive than merely checking
-// whether newVals.VerifyCommit(...), in fact it calls exactly that.
-func (vals *ValidatorSet) VerifyFutureCommit(newVals *ValidatorSet, chainID string,
-	blockID BlockID, height int64, commit *Commit) error {
-	oldVals := vals
-
-	// Commit must be a valid commit for newVals.
-	err := newVals.VerifyCommit(chainID, blockID, height, commit)
-	if err != nil {
-		return err
-	}
-
-	// Check old voting power.
-	oldVotingPower := int64(0)
-	seen := map[int]bool{}
-	round := commit.Round()
-
-	for idx, precommit := range commit.Precommits {
-		if precommit == nil {
-			continue
-		}
-		if precommit.Height != height {
-			return cmn.NewError("Blocks don't match - %d vs %d", round, precommit.Round)
-		}
-		if precommit.Round != round {
-			return cmn.NewError("Invalid commit -- wrong round: %v vs %v", round, precommit.Round)
-		}
-		if precommit.Type != PrecommitType {
-			return cmn.NewError("Invalid commit -- not precommit @ index %v", idx)
-		}
-		// See if this validator is in oldVals.
-		oldIdx, val := oldVals.GetByAddress(precommit.ValidatorAddress)
-		if val == nil || seen[oldIdx] {
-			continue // missing or double vote...
-		}
-		seen[oldIdx] = true
-
-		// Validate signature.
-		precommitSignBytes := commit.VoteSignBytes(chainID, idx)
-		if !val.PubKey.VerifyBytes(precommitSignBytes, precommit.Signature) {
-			return cmn.NewError("Invalid commit -- invalid signature: %v", precommit)
-		}
-		// Good precommit!
-		if blockID.Equals(precommit.BlockID) {
-			oldVotingPower += val.VotingPower
-		} else {
-			// It's OK that the BlockID doesn't match.  We include stray
-			// precommits to measure validator availability.
-		}
-	}
-
-	if oldVotingPower <= oldVals.TotalVotingPower()*2/3 {
-		return errTooMuchChange{oldVotingPower, oldVals.TotalVotingPower()*2/3 + 1}
-	}
-	return nil
-}
-
 //-----------------
 // ErrTooMuchChange