From 5b14a73708b3541d64a06a340eb3083fb16deac6 Mon Sep 17 00:00:00 2001
From: iquidus <luke@iquidus.io>
Date: Fri, 13 Nov 2020 17:50:59 +0100
Subject: [PATCH] ethash/sealer: use epoch boundary + 1 (not block number) for
 seedHash in makeWork - fixes #234

---
 consensus/ethash/algorithm.go | 3 ++-
 consensus/ethash/sealer.go    | 4 +++-
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/consensus/ethash/algorithm.go b/consensus/ethash/algorithm.go
index 2593e29e4cd2a..c6ad295e160f1 100644
--- a/consensus/ethash/algorithm.go
+++ b/consensus/ethash/algorithm.go
@@ -133,7 +133,8 @@ func makeHasher(h hash.Hash) hasher {
 }
 
 // seedHash is the seed to use for generating a verification cache and the mining
-// dataset.
+// dataset. The block number passed should be pre-rounded to an epoch boundary + 1
+// e.g: epoch * epochLength + 1
 func seedHash(block uint64) []byte {
 	seed := make([]byte, 32)
 	if block < epochLengthDefault {
diff --git a/consensus/ethash/sealer.go b/consensus/ethash/sealer.go
index 205353402852e..08f6db8c980cd 100644
--- a/consensus/ethash/sealer.go
+++ b/consensus/ethash/sealer.go
@@ -344,8 +344,10 @@ func (s *remoteSealer) loop() {
 //   result[3], hex encoded block number
 func (s *remoteSealer) makeWork(block *types.Block) {
 	hash := s.ethash.SealHash(block.Header())
+	epochLength := calcEpochLength(block.NumberU64(), s.ethash.config.ECIP1099Block)
+	epoch := calcEpoch(block.NumberU64(), epochLength)
 	s.currentWork[0] = hash.Hex()
-	s.currentWork[1] = common.BytesToHash(SeedHash(block.NumberU64())).Hex()
+	s.currentWork[1] = common.BytesToHash(SeedHash(epoch*epochLength + 1)).Hex()
 	s.currentWork[2] = common.BytesToHash(new(big.Int).Div(two256, block.Difficulty()).Bytes()).Hex()
 	s.currentWork[3] = hexutil.EncodeBig(block.Number())