From 0ef30140253a2c9e8cfb0e593143b6d950625521 Mon Sep 17 00:00:00 2001
From: Aidan <aidan.kwon@klaytn.foundation>
Date: Thu, 7 Dec 2023 17:01:46 +0800
Subject: [PATCH 01/11] Refine code and comments

---
 consensus/istanbul/backend/engine.go   |  6 ++---
 consensus/istanbul/backend/randao.go   | 31 +++++++++++++++-----------
 consensus/istanbul/backend/snapshot.go | 22 +++++-------------
 params/config.go                       |  9 --------
 4 files changed, 26 insertions(+), 42 deletions(-)

diff --git a/consensus/istanbul/backend/engine.go b/consensus/istanbul/backend/engine.go
index c465d9fb23..8873b71c8a 100644
--- a/consensus/istanbul/backend/engine.go
+++ b/consensus/istanbul/backend/engine.go
@@ -254,8 +254,7 @@ func (sb *backend) verifyCascadingFields(chain consensus.ChainReader, header *ty
 
 	// VerifyRandao must be after verifySigner because it needs the signer (proposer) address
 	if chain.Config().IsRandaoForkEnabled(header.Number) {
-		prevMixHash := headerMixHash(chain, parent)
-		if err := sb.VerifyRandao(chain, header, prevMixHash); err != nil {
+		if err := sb.VerifyRandao(chain, header, parent.MixHash); err != nil {
 			return err
 		}
 	} else if header.RandomReveal != nil || header.MixHash != nil {
@@ -438,8 +437,7 @@ func (sb *backend) Prepare(chain consensus.ChainReader, header *types.Header) er
 	}
 
 	if chain.Config().IsRandaoForkEnabled(header.Number) {
-		prevMixHash := headerMixHash(chain, parent)
-		randomReveal, mixHash, err := sb.CalcRandao(header.Number, prevMixHash)
+		randomReveal, mixHash, err := sb.CalcRandao(header.Number, parent.MixHash)
 		if err != nil {
 			return err
 		}
diff --git a/consensus/istanbul/backend/randao.go b/consensus/istanbul/backend/randao.go
index ece8f16cad..d7a62a8f97 100644
--- a/consensus/istanbul/backend/randao.go
+++ b/consensus/istanbul/backend/randao.go
@@ -36,10 +36,10 @@ func newChainBlsPubkeyProvider() *ChainBlsPubkeyProvider {
 	}
 }
 
-// The default implementation for BlsPubkeyFunc.
+// GetBlsPubkey is the default implementation for BlsPubkeyFunc.
 // Queries KIP-113 contract and verifies the PoP.
 func (p *ChainBlsPubkeyProvider) GetBlsPubkey(chain consensus.ChainReader, proposer common.Address, num *big.Int) (bls.PublicKey, error) {
-	infos, err := p.getAllCached(chain, num)
+	infos, err := p.getBlsInfos(chain, num)
 	if err != nil {
 		return nil, err
 	}
@@ -54,7 +54,9 @@ func (p *ChainBlsPubkeyProvider) GetBlsPubkey(chain consensus.ChainReader, propo
 	return bls.PublicKeyFromBytes(info.PublicKey)
 }
 
-func (p *ChainBlsPubkeyProvider) getAllCached(chain consensus.ChainReader, num *big.Int) (system.BlsPublicKeyInfos, error) {
+// getBlsInfosv returns all registered BLS info at the given block number.
+// It retrieves cache first, and then retrieves the storage of KIP113 contract.
+func (p *ChainBlsPubkeyProvider) getBlsInfos(chain consensus.ChainReader, num *big.Int) (system.BlsPublicKeyInfos, error) {
 	if item, ok := p.cache.Get(num.Uint64()); ok {
 		logger.Trace("BlsPublicKeyInfos cache hit", "number", num.Uint64())
 		return item.(system.BlsPublicKeyInfos), nil
@@ -100,12 +102,15 @@ func (p *ChainBlsPubkeyProvider) ResetBlsCache() {
 	p.cache.Purge()
 }
 
-// Calculate KIP-114 Randao header fields
+// CalcRandao calculates Randao-related header values specified in KIP-114.
 // https://github.com/klaytn/kips/blob/kip114/KIPs/kip-114.md
 func (sb *backend) CalcRandao(number *big.Int, prevMixHash []byte) ([]byte, []byte, error) {
 	if sb.blsSecretKey == nil {
 		return nil, nil, errNoBlsKey
 	}
+	if prevMixHash == nil {
+		prevMixHash = params.ZeroMixHash
+	}
 	if len(prevMixHash) != 32 {
 		logger.Error("invalid prevMixHash", "number", number.Uint64(), "prevMixHash", hexutil.Encode(prevMixHash))
 		return nil, nil, errInvalidRandaoFields
@@ -123,10 +128,19 @@ func (sb *backend) CalcRandao(number *big.Int, prevMixHash []byte) ([]byte, []by
 	return randomReveal, mixHash, nil
 }
 
+// VerifyRandao verifies whether header.RandomReveal is the same as expected.
 func (sb *backend) VerifyRandao(chain consensus.ChainReader, header *types.Header, prevMixHash []byte) error {
 	if header.Number.Sign() == 0 {
 		return nil // Do not verify genesis block
 	}
+	if header.RandomReveal == nil || header.MixHash == nil {
+		return errInvalidRandaoFields
+	}
+	// The following condition is only true when header's block number is the Randao hardfork block number.
+	// Because of the above condition, prevMixHash cannot be nil after Randao hardfork block.
+	if prevMixHash == nil {
+		prevMixHash = params.ZeroMixHash
+	}
 
 	proposer, err := sb.Author(header)
 	if err != nil {
@@ -173,12 +187,3 @@ func calcMixHash(randomReveal, prevMixHash []byte) []byte {
 	}
 	return mixHash
 }
-
-// At the fork block's parent, pretend that prevMixHash is ZeroMixHash.
-func headerMixHash(chain consensus.ChainReader, header *types.Header) []byte {
-	if chain.Config().IsRandaoForkBlockParent(header.Number) {
-		return params.ZeroMixHash
-	} else {
-		return header.MixHash
-	}
-}
diff --git a/consensus/istanbul/backend/snapshot.go b/consensus/istanbul/backend/snapshot.go
index ef0f64771d..ec4e3777b8 100644
--- a/consensus/istanbul/backend/snapshot.go
+++ b/consensus/istanbul/backend/snapshot.go
@@ -23,7 +23,6 @@ package backend
 import (
 	"bytes"
 	"encoding/json"
-	"math/big"
 
 	"github.com/klaytn/klaytn/consensus"
 
@@ -220,22 +219,13 @@ func (s *Snapshot) apply(headers []*types.Header, gov governance.Engine, addr co
 			}
 		}
 	}
-	snap.Number += uint64(len(headers))
-	snap.Hash = headers[len(headers)-1].Hash()
-
-	if snap.ValSet.Policy() == istanbul.WeightedRandom {
-		snap.ValSet.SetBlockNum(snap.Number)
-
-		bigNum := new(big.Int).SetUint64(snap.Number)
-		if chain.Config().IsRandaoForkBlockParent(bigNum) {
-			// The ForkBlock must select proposers using MixHash but (ForkBlock - 1) has no MixHash. Using ZeroMixHash instead.
-			snap.ValSet.SetMixHash(params.ZeroMixHash)
-		} else if chain.Config().IsRandaoForkEnabled(bigNum) {
-			// Feed parent MixHash
-			snap.ValSet.SetMixHash(headers[len(headers)-1].MixHash)
-		}
-	}
+	lastHeader := headers[len(headers)-1]
+	snap.Number = lastHeader.Number.Uint64()
+	snap.Hash = lastHeader.Hash()
+
+	snap.ValSet.SetBlockNum(snap.Number)
 	snap.ValSet.SetSubGroupSize(snap.CommitteeSize)
+	snap.ValSet.SetMixHash(lastHeader.MixHash)
 
 	if writable {
 		gov.SetTotalVotingPower(snap.ValSet.TotalVotingPower())
diff --git a/params/config.go b/params/config.go
index 0a8235de79..c947adb0f6 100644
--- a/params/config.go
+++ b/params/config.go
@@ -400,15 +400,6 @@ func (c *ChainConfig) IsKIP103ForkBlock(num *big.Int) bool {
 	return c.Kip103CompatibleBlock.Cmp(num) == 0
 }
 
-// IsRandaoForkBlockParent returns whethere num is one block before the randao block.
-func (c *ChainConfig) IsRandaoForkBlockParent(num *big.Int) bool {
-	if c.RandaoCompatibleBlock == nil || num == nil {
-		return false
-	}
-	nextNum := new(big.Int).Add(num, common.Big1)
-	return c.RandaoCompatibleBlock.Cmp(nextNum) == 0 // randao == num + 1
-}
-
 // IsRandaoForkBlock returns whether num is equal to the randao block.
 func (c *ChainConfig) IsRandaoForkBlock(num *big.Int) bool {
 	if c.RandaoCompatibleBlock == nil || num == nil {

From 8a69068cfc6b84f46633e4389080bac1de23358e Mon Sep 17 00:00:00 2001
From: Aidan <aidan.kwon@klaytn.foundation>
Date: Thu, 7 Dec 2023 17:18:37 +0800
Subject: [PATCH 02/11] Additional comments for Randao HF prerequisites

---
 params/config.go | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/params/config.go b/params/config.go
index c947adb0f6..29fd9c712e 100644
--- a/params/config.go
+++ b/params/config.go
@@ -200,7 +200,11 @@ type ChainConfig struct {
 	Kip103ContractAddress common.Address `json:"kip103ContractAddress,omitempty"` // Kip103 contract address already deployed on the network
 
 	// Randao is an optional hardfork
-	// RandaoCompatibleBlock, RandaoRegistryRecords and RandaoRegistryOwner all must be specified to enable Randao
+	// RandaoCompatibleBlock, RandaoRegistryRecords and RandaoRegistryOwner all must be specified to enable Randao.
+	// Since Rando also enables KIP113 (BLS registry) simultaneously, the followings should be done before the hardfork.
+	//   - BLS contract (KIP113) should be deployed
+	//   - Validators information should be registered on the BLS contract
+	//   - Randao registry should be specified with the KIP113 contract address
 	RandaoCompatibleBlock *big.Int        `json:"randaoCompatibleBlock,omitempty"` // RandaoCompatible activate block (nil = no fork)
 	RandaoRegistry        *RegistryConfig `json:"randaoRegistry,omitempty"`        // Registry initial states
 

From b800f95d2178f8ca99516d94d8972f899ddb0c46 Mon Sep 17 00:00:00 2001
From: Aidan <aidan.kwon@klaytn.foundation>
Date: Thu, 7 Dec 2023 18:15:49 +0800
Subject: [PATCH 03/11] fix test failure

---
 consensus/istanbul/backend/randao.go   | 20 +++++++++++---------
 consensus/istanbul/backend/snapshot.go |  5 ++++-
 2 files changed, 15 insertions(+), 10 deletions(-)

diff --git a/consensus/istanbul/backend/randao.go b/consensus/istanbul/backend/randao.go
index d7a62a8f97..19944f424c 100644
--- a/consensus/istanbul/backend/randao.go
+++ b/consensus/istanbul/backend/randao.go
@@ -108,11 +108,12 @@ func (sb *backend) CalcRandao(number *big.Int, prevMixHash []byte) ([]byte, []by
 	if sb.blsSecretKey == nil {
 		return nil, nil, errNoBlsKey
 	}
-	if prevMixHash == nil {
-		prevMixHash = params.ZeroMixHash
+	parentMixHash := prevMixHash
+	if parentMixHash == nil {
+		parentMixHash = params.ZeroMixHash
 	}
-	if len(prevMixHash) != 32 {
-		logger.Error("invalid prevMixHash", "number", number.Uint64(), "prevMixHash", hexutil.Encode(prevMixHash))
+	if len(parentMixHash) != 32 {
+		logger.Error("invalid prevMixHash", "number", number.Uint64(), "prevMixHash", hexutil.Encode(parentMixHash))
 		return nil, nil, errInvalidRandaoFields
 	}
 
@@ -123,7 +124,7 @@ func (sb *backend) CalcRandao(number *big.Int, prevMixHash []byte) ([]byte, []by
 	randomReveal := bls.Sign(sb.blsSecretKey, msg[:]).Marshal()
 
 	// calc_mix_hash() = xor(prevMixHash, keccak256(randomReveal))
-	mixHash := calcMixHash(randomReveal, prevMixHash)
+	mixHash := calcMixHash(randomReveal, parentMixHash)
 
 	return randomReveal, mixHash, nil
 }
@@ -136,10 +137,11 @@ func (sb *backend) VerifyRandao(chain consensus.ChainReader, header *types.Heade
 	if header.RandomReveal == nil || header.MixHash == nil {
 		return errInvalidRandaoFields
 	}
-	// The following condition is only true when header's block number is the Randao hardfork block number.
+	// The following if condition is only true when header's block number is the Randao hardfork block number.
 	// Because of the above condition, prevMixHash cannot be nil after Randao hardfork block.
-	if prevMixHash == nil {
-		prevMixHash = params.ZeroMixHash
+	parentMixHash := prevMixHash
+	if parentMixHash == nil {
+		parentMixHash = params.ZeroMixHash
 	}
 
 	proposer, err := sb.Author(header)
@@ -165,7 +167,7 @@ func (sb *backend) VerifyRandao(chain consensus.ChainReader, header *types.Heade
 	}
 
 	// if not newHeader.mixHash == calc_mix_hash(prevMixHash, newHeader.randomReveal): return False
-	mixHash := calcMixHash(header.RandomReveal, prevMixHash)
+	mixHash := calcMixHash(header.RandomReveal, parentMixHash)
 	if !bytes.Equal(header.MixHash, mixHash) {
 		return errInvalidRandaoFields
 	}
diff --git a/consensus/istanbul/backend/snapshot.go b/consensus/istanbul/backend/snapshot.go
index ec4e3777b8..b194592330 100644
--- a/consensus/istanbul/backend/snapshot.go
+++ b/consensus/istanbul/backend/snapshot.go
@@ -225,7 +225,10 @@ func (s *Snapshot) apply(headers []*types.Header, gov governance.Engine, addr co
 
 	snap.ValSet.SetBlockNum(snap.Number)
 	snap.ValSet.SetSubGroupSize(snap.CommitteeSize)
-	snap.ValSet.SetMixHash(lastHeader.MixHash)
+
+	if chain.Config().IsRandaoForkEnabled(lastHeader.Number) {
+		snap.ValSet.SetMixHash(lastHeader.MixHash)
+	}
 
 	if writable {
 		gov.SetTotalVotingPower(snap.ValSet.TotalVotingPower())

From c51ac91e35974ca01c56b33306002317ea171d61 Mon Sep 17 00:00:00 2001
From: Aidan <aidan.kwon@klaytn.foundation>
Date: Fri, 8 Dec 2023 09:55:44 +0800
Subject: [PATCH 04/11] handle nil mixHash in weightedRandomProposer func, and
 fix typo

---
 consensus/istanbul/validator/weighted.go | 12 ++++++------
 params/config.go                         |  2 +-
 2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/consensus/istanbul/validator/weighted.go b/consensus/istanbul/validator/weighted.go
index db48ce77e5..35444f0a44 100644
--- a/consensus/istanbul/validator/weighted.go
+++ b/consensus/istanbul/validator/weighted.go
@@ -276,13 +276,13 @@ func weightedRandomProposer(valSet istanbul.ValidatorSet, lastProposer common.Ad
 	rules := fork.Rules(new(big.Int).SetUint64(weightedCouncil.blockNum + 1))
 	// After Randao: Select one from ValidatorSet using MixHash as a seed.
 	if rules.IsRandao {
-		if weightedCouncil.mixHash == nil {
-			logger.Error("no mixHash", "number", weightedCouncil.blockNum)
-			return nil
+		mixHash := weightedCouncil.mixHash
+		if mixHash == nil {
+			mixHash = params.ZeroMixHash
 		}
 		// def proposer_selector(validators, committee_size, round, seed):
 		// select_committee_KIP146(validators, committee_size, seed)[round % len(validators)]
-		committee := SelectRandaoCommittee(weightedCouncil.List(), weightedCouncil.subSize, weightedCouncil.mixHash)
+		committee := SelectRandaoCommittee(weightedCouncil.List(), weightedCouncil.subSize, mixHash)
 		return committee[round%uint64(len(committee))]
 	}
 
@@ -783,8 +783,8 @@ func filterValidators(isSingleMode bool, govNodeAddr common.Address, weightedVal
 
 // getStakingAmountsOfValidators calculates stakingAmounts of validators.
 // If validators have multiple staking contracts, stakingAmounts will be a sum of stakingAmounts with the same rewardAddress.
-//  - []*weightedValidator : a list of validators which type is converted to weightedValidator
-//  - []float64 : a list of stakingAmounts.
+//   - []*weightedValidator : a list of validators which type is converted to weightedValidator
+//   - []float64 : a list of stakingAmounts.
 func getStakingAmountsOfValidators(validators istanbul.Validators, stakingInfo *reward.StakingInfo) ([]*weightedValidator, []float64, error) {
 	nVals := len(validators)
 	weightedVals := make([]*weightedValidator, nVals)
diff --git a/params/config.go b/params/config.go
index 29fd9c712e..3d64100f3f 100644
--- a/params/config.go
+++ b/params/config.go
@@ -201,7 +201,7 @@ type ChainConfig struct {
 
 	// Randao is an optional hardfork
 	// RandaoCompatibleBlock, RandaoRegistryRecords and RandaoRegistryOwner all must be specified to enable Randao.
-	// Since Rando also enables KIP113 (BLS registry) simultaneously, the followings should be done before the hardfork.
+	// Since Randao also enables KIP113 (BLS registry) simultaneously, the followings should be done before the hardfork.
 	//   - BLS contract (KIP113) should be deployed
 	//   - Validators information should be registered on the BLS contract
 	//   - Randao registry should be specified with the KIP113 contract address

From f14b7463d7bb28cd1a55361758e7b6a722113943 Mon Sep 17 00:00:00 2001
From: Aidan <aidan.kwon@klaytn.foundation>
Date: Fri, 8 Dec 2023 11:22:07 +0800
Subject: [PATCH 05/11] handle nil mixHash in SubListWithProposer and update a
 test case

---
 consensus/istanbul/validator/weighted.go          |  8 ++++----
 .../istanbul/validator/weighted_random_test.go    | 15 ++++++++-------
 2 files changed, 12 insertions(+), 11 deletions(-)

diff --git a/consensus/istanbul/validator/weighted.go b/consensus/istanbul/validator/weighted.go
index 35444f0a44..4bb7ab96e7 100644
--- a/consensus/istanbul/validator/weighted.go
+++ b/consensus/istanbul/validator/weighted.go
@@ -379,14 +379,14 @@ func (valSet *weightedCouncil) SubListWithProposer(prevHash common.Hash, propose
 	if fork.Rules(view.Sequence).IsRandao {
 		// This committee must include proposers for all rounds because
 		// the proposer is picked from the this committee. See weightedRandomProposer().
-		if valSet.mixHash == nil {
-			logger.Error("no mixHash", "number", valSet.blockNum)
-			return nil
+		mixHash := valSet.mixHash
+		if mixHash == nil {
+			mixHash = params.ZeroMixHash
 		}
 		// def select_committee_KIP146(validators, committee_size, seed):
 		// shuffled = shuffle_validators_KIP146(validators, seed)
 		// return shuffled[:min(committee_size, len(validators))]
-		return SelectRandaoCommittee(validators, committeeSize, valSet.mixHash)
+		return SelectRandaoCommittee(validators, committeeSize, mixHash)
 	}
 
 	// Before Randao: SelectRandomCommittee, but the first two members are proposer and next proposer
diff --git a/consensus/istanbul/validator/weighted_random_test.go b/consensus/istanbul/validator/weighted_random_test.go
index 282038144d..4dcad5fb5a 100644
--- a/consensus/istanbul/validator/weighted_random_test.go
+++ b/consensus/istanbul/validator/weighted_random_test.go
@@ -580,13 +580,14 @@ func TestWeightedCouncil_Randao(t *testing.T) {
 			expectedProposer:  SelectRandaoCommittee(validators, valSize+1, testMixHash)[0],
 			expectedCommittee: validators,
 		},
-		{ // nil MixHash
-			blockNum:          forkNum + 10, // expect log "no mixHash  number=(forkNum+10)"
-			round:             0,
-			committeeSize:     valSize - 1,
-			mixHash:           nil,
-			expectedProposer:  validators[0], // fall back to roundRobinProposer
-			expectedCommittee: nil,           // SubList fails.
+		{ // nil MixHash (this case should not happen)
+			blockNum:      forkNum + 10, // expect log "no mixHash  number=(forkNum+10)"
+			round:         0,
+			committeeSize: valSize - 1,
+			mixHash:       nil,
+			// fall back to calculate proposer with zeroMixHash
+			expectedProposer:  SelectRandaoCommittee(validators, valSize-1, params.ZeroMixHash)[0],
+			expectedCommittee: SelectRandaoCommittee(validators, valSize-1, params.ZeroMixHash),
 		},
 		{ // IsSubset() == true
 			blockNum:          forkNum,

From 680495ed9ce43f40b3d73929fb3f2011c7832977 Mon Sep 17 00:00:00 2001
From: Aidan <aidan.kwon@klaytn.foundation>
Date: Fri, 8 Dec 2023 11:30:33 +0800
Subject: [PATCH 06/11] update comments for a test case

---
 consensus/istanbul/validator/weighted_random_test.go | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/consensus/istanbul/validator/weighted_random_test.go b/consensus/istanbul/validator/weighted_random_test.go
index 4dcad5fb5a..09a74b2007 100644
--- a/consensus/istanbul/validator/weighted_random_test.go
+++ b/consensus/istanbul/validator/weighted_random_test.go
@@ -580,12 +580,11 @@ func TestWeightedCouncil_Randao(t *testing.T) {
 			expectedProposer:  SelectRandaoCommittee(validators, valSize+1, testMixHash)[0],
 			expectedCommittee: validators,
 		},
-		{ // nil MixHash (this case should not happen)
-			blockNum:      forkNum + 10, // expect log "no mixHash  number=(forkNum+10)"
-			round:         0,
-			committeeSize: valSize - 1,
-			mixHash:       nil,
-			// fall back to calculate proposer with zeroMixHash
+		{ // nil MixHash (expected MixHash value at fork block number)
+			blockNum:          forkNum,
+			round:             0,
+			committeeSize:     valSize - 1,
+			mixHash:           nil, // If rules.IsRandao && mixHash == nil, then ZeroMixHash is used
 			expectedProposer:  SelectRandaoCommittee(validators, valSize-1, params.ZeroMixHash)[0],
 			expectedCommittee: SelectRandaoCommittee(validators, valSize-1, params.ZeroMixHash),
 		},

From da4cbeb53da2505db33adfa05cd2ff9f69ac8d38 Mon Sep 17 00:00:00 2001
From: Aidan <aidan.kwon@klaytn.foundation>
Date: Fri, 8 Dec 2023 11:43:44 +0800
Subject: [PATCH 07/11] update comments

---
 consensus/istanbul/backend/randao.go | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/consensus/istanbul/backend/randao.go b/consensus/istanbul/backend/randao.go
index 19944f424c..07688d8788 100644
--- a/consensus/istanbul/backend/randao.go
+++ b/consensus/istanbul/backend/randao.go
@@ -17,7 +17,7 @@ import (
 	"github.com/klaytn/klaytn/params"
 )
 
-// For testing without KIP-113 contract setup
+// BlsPubkeyProvider allows introducing a ChainBlsPubkeyProvider mock to be used for testing
 type BlsPubkeyProvider interface {
 	// num should be the header number of the block to be verified.
 	// Thus, since the state of num does not exist, the state of num-1 must be used.
@@ -25,6 +25,7 @@ type BlsPubkeyProvider interface {
 	ResetBlsCache()
 }
 
+// ChainBlsPubkeyProvider is the default implementation for BlsPubkeyProvider.
 type ChainBlsPubkeyProvider struct {
 	cache *lru.ARCCache // Cached BlsPublicKeyInfos
 }
@@ -36,7 +37,7 @@ func newChainBlsPubkeyProvider() *ChainBlsPubkeyProvider {
 	}
 }
 
-// GetBlsPubkey is the default implementation for BlsPubkeyFunc.
+// GetBlsPubkey retrieves a BLS public key stored in blockchain.
 // Queries KIP-113 contract and verifies the PoP.
 func (p *ChainBlsPubkeyProvider) GetBlsPubkey(chain consensus.ChainReader, proposer common.Address, num *big.Int) (bls.PublicKey, error) {
 	infos, err := p.getBlsInfos(chain, num)
@@ -54,7 +55,7 @@ func (p *ChainBlsPubkeyProvider) GetBlsPubkey(chain consensus.ChainReader, propo
 	return bls.PublicKeyFromBytes(info.PublicKey)
 }
 
-// getBlsInfosv returns all registered BLS info at the given block number.
+// getBlsInfos returns all registered BLS info at the given block number.
 // It retrieves cache first, and then retrieves the storage of KIP113 contract.
 func (p *ChainBlsPubkeyProvider) getBlsInfos(chain consensus.ChainReader, num *big.Int) (system.BlsPublicKeyInfos, error) {
 	if item, ok := p.cache.Get(num.Uint64()); ok {
@@ -129,7 +130,7 @@ func (sb *backend) CalcRandao(number *big.Int, prevMixHash []byte) ([]byte, []by
 	return randomReveal, mixHash, nil
 }
 
-// VerifyRandao verifies whether header.RandomReveal is the same as expected.
+// VerifyRandao verifies whether Randao-related header values conform to KIP-114.
 func (sb *backend) VerifyRandao(chain consensus.ChainReader, header *types.Header, prevMixHash []byte) error {
 	if header.Number.Sign() == 0 {
 		return nil // Do not verify genesis block
@@ -137,8 +138,9 @@ func (sb *backend) VerifyRandao(chain consensus.ChainReader, header *types.Heade
 	if header.RandomReveal == nil || header.MixHash == nil {
 		return errInvalidRandaoFields
 	}
-	// The following if condition is only true when header's block number is the Randao hardfork block number.
-	// Because of the above condition, prevMixHash cannot be nil after Randao hardfork block.
+	// The VerifyRandao is invoked only since Randao hardfork block number.
+	// Since Randao hardfork, the header fields are cannot be nil because of the check above (header.RandomReveal == nil || header.MixHash == nil).
+	// Therefore it's safe to assume that if prevMixHash == nil, then the given header is exactly Randao hardfork block number.
 	parentMixHash := prevMixHash
 	if parentMixHash == nil {
 		parentMixHash = params.ZeroMixHash

From 0df72fd707667d74054403c755137e200e094bbf Mon Sep 17 00:00:00 2001
From: Aidan <aidan.kwon@klaytn.foundation>
Date: Fri, 8 Dec 2023 12:14:35 +0800
Subject: [PATCH 08/11] Change nil header.mixHash checking mothod to check the
 length

---
 blockchain/evm.go                        |  2 +-
 consensus/istanbul/backend/randao.go     | 12 +++++++-----
 consensus/istanbul/validator/weighted.go |  4 ++--
 3 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/blockchain/evm.go b/blockchain/evm.go
index a0d27f23fd..b8e922c85e 100644
--- a/blockchain/evm.go
+++ b/blockchain/evm.go
@@ -69,7 +69,7 @@ func NewEVMBlockContext(header *types.Header, chain ChainContext, author *common
 		baseFee = new(big.Int).SetUint64(params.ZeroBaseFee)
 	}
 
-	if header.MixHash != nil {
+	if len(header.MixHash) != 0 {
 		random = common.BytesToHash(header.MixHash)
 	} else { // Before Randao hardfork, RANDOM (44) returns last block hash
 		random = header.ParentHash
diff --git a/consensus/istanbul/backend/randao.go b/consensus/istanbul/backend/randao.go
index 07688d8788..fb933560d0 100644
--- a/consensus/istanbul/backend/randao.go
+++ b/consensus/istanbul/backend/randao.go
@@ -110,7 +110,7 @@ func (sb *backend) CalcRandao(number *big.Int, prevMixHash []byte) ([]byte, []by
 		return nil, nil, errNoBlsKey
 	}
 	parentMixHash := prevMixHash
-	if parentMixHash == nil {
+	if len(parentMixHash) == 0 {
 		parentMixHash = params.ZeroMixHash
 	}
 	if len(parentMixHash) != 32 {
@@ -135,17 +135,19 @@ func (sb *backend) VerifyRandao(chain consensus.ChainReader, header *types.Heade
 	if header.Number.Sign() == 0 {
 		return nil // Do not verify genesis block
 	}
-	if header.RandomReveal == nil || header.MixHash == nil {
-		return errInvalidRandaoFields
-	}
+
 	// The VerifyRandao is invoked only since Randao hardfork block number.
 	// Since Randao hardfork, the header fields are cannot be nil because of the check above (header.RandomReveal == nil || header.MixHash == nil).
 	// Therefore it's safe to assume that if prevMixHash == nil, then the given header is exactly Randao hardfork block number.
 	parentMixHash := prevMixHash
-	if parentMixHash == nil {
+	if len(parentMixHash) == 0 {
 		parentMixHash = params.ZeroMixHash
 	}
 
+	if len(header.RandomReveal) != 96 || len(header.MixHash) != 32 {
+		return errInvalidRandaoFields
+	}
+
 	proposer, err := sb.Author(header)
 	if err != nil {
 		return err
diff --git a/consensus/istanbul/validator/weighted.go b/consensus/istanbul/validator/weighted.go
index 4bb7ab96e7..3dadbfb4c4 100644
--- a/consensus/istanbul/validator/weighted.go
+++ b/consensus/istanbul/validator/weighted.go
@@ -277,7 +277,7 @@ func weightedRandomProposer(valSet istanbul.ValidatorSet, lastProposer common.Ad
 	// After Randao: Select one from ValidatorSet using MixHash as a seed.
 	if rules.IsRandao {
 		mixHash := weightedCouncil.mixHash
-		if mixHash == nil {
+		if len(mixHash) == 0 {
 			mixHash = params.ZeroMixHash
 		}
 		// def proposer_selector(validators, committee_size, round, seed):
@@ -380,7 +380,7 @@ func (valSet *weightedCouncil) SubListWithProposer(prevHash common.Hash, propose
 		// This committee must include proposers for all rounds because
 		// the proposer is picked from the this committee. See weightedRandomProposer().
 		mixHash := valSet.mixHash
-		if mixHash == nil {
+		if len(mixHash) == 0 {
 			mixHash = params.ZeroMixHash
 		}
 		// def select_committee_KIP146(validators, committee_size, seed):

From 37b74adcf3636c3cd58d98a482088ae521375f0b Mon Sep 17 00:00:00 2001
From: Aidan <aidan.kwon@klaytn.foundation>
Date: Fri, 8 Dec 2023 13:23:34 +0800
Subject: [PATCH 09/11] minor code adjustment

---
 consensus/istanbul/backend/randao.go | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/consensus/istanbul/backend/randao.go b/consensus/istanbul/backend/randao.go
index fb933560d0..c199a112db 100644
--- a/consensus/istanbul/backend/randao.go
+++ b/consensus/istanbul/backend/randao.go
@@ -136,6 +136,10 @@ func (sb *backend) VerifyRandao(chain consensus.ChainReader, header *types.Heade
 		return nil // Do not verify genesis block
 	}
 
+	if len(header.RandomReveal) != 96 || len(header.MixHash) != 32 {
+		return errInvalidRandaoFields
+	}
+
 	// The VerifyRandao is invoked only since Randao hardfork block number.
 	// Since Randao hardfork, the header fields are cannot be nil because of the check above (header.RandomReveal == nil || header.MixHash == nil).
 	// Therefore it's safe to assume that if prevMixHash == nil, then the given header is exactly Randao hardfork block number.
@@ -144,10 +148,6 @@ func (sb *backend) VerifyRandao(chain consensus.ChainReader, header *types.Heade
 		parentMixHash = params.ZeroMixHash
 	}
 
-	if len(header.RandomReveal) != 96 || len(header.MixHash) != 32 {
-		return errInvalidRandaoFields
-	}
-
 	proposer, err := sb.Author(header)
 	if err != nil {
 		return err

From 740f92fe9c8db1d60089dfc232d2d7f46b1aec5a Mon Sep 17 00:00:00 2001
From: Aidan <aidan.kwon@klaytn.foundation>
Date: Fri, 8 Dec 2023 13:27:02 +0800
Subject: [PATCH 10/11] minor refinement

---
 consensus/istanbul/backend/snapshot.go | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/consensus/istanbul/backend/snapshot.go b/consensus/istanbul/backend/snapshot.go
index b194592330..30e525d45e 100644
--- a/consensus/istanbul/backend/snapshot.go
+++ b/consensus/istanbul/backend/snapshot.go
@@ -226,7 +226,7 @@ func (s *Snapshot) apply(headers []*types.Header, gov governance.Engine, addr co
 	snap.ValSet.SetBlockNum(snap.Number)
 	snap.ValSet.SetSubGroupSize(snap.CommitteeSize)
 
-	if chain.Config().IsRandaoForkEnabled(lastHeader.Number) {
+	if len(lastHeader.MixHash) != 0 { // After Rando HF
 		snap.ValSet.SetMixHash(lastHeader.MixHash)
 	}
 

From eb99234c237f5bcfaa3370ca3d912322fd597820 Mon Sep 17 00:00:00 2001
From: Aidan <aidan.kwon@klaytn.foundation>
Date: Fri, 8 Dec 2023 13:59:22 +0800
Subject: [PATCH 11/11] Safe mixHash assigment for nil value

---
 api/api_ethereum.go                      |  6 ++++--
 api/api_public_blockchain.go             |  6 ++++--
 consensus/istanbul/backend/engine.go     |  4 +++-
 consensus/istanbul/backend/snapshot.go   |  4 +++-
 consensus/istanbul/validator/weighted.go | 10 +++++++---
 node/cn/filters/api.go                   |  4 +++-
 6 files changed, 24 insertions(+), 10 deletions(-)

diff --git a/api/api_ethereum.go b/api/api_ethereum.go
index ea07327eeb..8f004360e4 100644
--- a/api/api_ethereum.go
+++ b/api/api_ethereum.go
@@ -1253,9 +1253,11 @@ func (api *EthereumAPI) rpcMarshalHeader(head *types.Header, inclMiner bool) (ma
 			result["baseFeePerGas"] = (*hexutil.Big)(head.BaseFee)
 		}
 	}
-	if b.ChainConfig().IsRandaoForkEnabled(head.Number) {
+	if len(head.RandomReveal) > 0 {
 		result["randomReveal"] = hexutil.Bytes(head.RandomReveal)
-		result["mixHash"] = hexutil.Bytes(head.MixHash)
+	}
+	if len(head.MixHash) > 0 {
+		result["mixhash"] = hexutil.Bytes(head.MixHash)
 	}
 	return result, nil
 }
diff --git a/api/api_public_blockchain.go b/api/api_public_blockchain.go
index d79ca6e051..1dc3639151 100644
--- a/api/api_public_blockchain.go
+++ b/api/api_public_blockchain.go
@@ -582,9 +582,11 @@ func RpcOutputBlock(b *types.Block, td *big.Int, inclTx bool, fullTx bool, rules
 			fields["baseFeePerGas"] = (*hexutil.Big)(head.BaseFee)
 		}
 	}
-	if rules.IsRandao {
+	if len(head.RandomReveal) > 0 {
 		fields["randomReveal"] = hexutil.Bytes(head.RandomReveal)
-		fields["mixHash"] = hexutil.Bytes(head.MixHash)
+	}
+	if len(head.MixHash) > 0 {
+		fields["mixhash"] = hexutil.Bytes(head.MixHash)
 	}
 
 	return fields, nil
diff --git a/consensus/istanbul/backend/engine.go b/consensus/istanbul/backend/engine.go
index 8873b71c8a..9a758f7b86 100644
--- a/consensus/istanbul/backend/engine.go
+++ b/consensus/istanbul/backend/engine.go
@@ -732,7 +732,9 @@ func (sb *backend) initSnapshot(chain consensus.ChainReader) (*Snapshot, error)
 	valSet := validator.NewValidatorSet(istanbulExtra.Validators, nil,
 		istanbul.ProposerPolicy(pset.Policy()),
 		pset.CommitteeSize(), chain)
-	valSet.SetMixHash(genesis.MixHash)
+	if len(genesis.MixHash) != 0 {
+		valSet.SetMixHash(genesis.MixHash)
+	}
 	snap := newSnapshot(sb.governance, 0, genesis.Hash(), valSet, chain.Config())
 
 	if err := snap.store(sb.db); err != nil {
diff --git a/consensus/istanbul/backend/snapshot.go b/consensus/istanbul/backend/snapshot.go
index 30e525d45e..ffa62b2834 100644
--- a/consensus/istanbul/backend/snapshot.go
+++ b/consensus/istanbul/backend/snapshot.go
@@ -359,7 +359,9 @@ func (s *Snapshot) UnmarshalJSON(b []byte) error {
 	if j.Policy == istanbul.WeightedRandom {
 		s.ValSet = validator.NewWeightedCouncil(j.Validators, j.DemotedValidators, j.RewardAddrs, j.VotingPowers, j.Weights, j.Policy, j.SubGroupSize, j.Number, j.ProposersBlockNum, nil)
 		validator.RecoverWeightedCouncilProposer(s.ValSet, j.Proposers)
-		s.ValSet.SetMixHash(j.MixHash)
+		if len(j.MixHash) != 0 {
+			s.ValSet.SetMixHash(j.MixHash)
+		}
 	} else {
 		s.ValSet = validator.NewSubSet(j.Validators, j.Policy, j.SubGroupSize)
 	}
diff --git a/consensus/istanbul/validator/weighted.go b/consensus/istanbul/validator/weighted.go
index 3dadbfb4c4..1d7447e607 100644
--- a/consensus/istanbul/validator/weighted.go
+++ b/consensus/istanbul/validator/weighted.go
@@ -259,7 +259,9 @@ func GetWeightedCouncilData(valSet istanbul.ValidatorSet) (validators []common.A
 			proposers[i] = proposer.Address()
 		}
 		proposersBlockNum = weightedCouncil.proposersBlockNum
-		mixHash = weightedCouncil.mixHash
+		if len(mixHash) != 0 {
+			mixHash = weightedCouncil.mixHash
+		}
 	} else {
 		logger.Error("invalid proposer policy for weightedCouncil")
 	}
@@ -628,8 +630,10 @@ func (valSet *weightedCouncil) Copy() istanbul.ValidatorSet {
 	newWeightedCouncil.proposers = make([]istanbul.Validator, len(valSet.proposers))
 	copy(newWeightedCouncil.proposers, valSet.proposers)
 
-	newWeightedCouncil.mixHash = make([]byte, len(valSet.mixHash))
-	copy(newWeightedCouncil.mixHash, valSet.mixHash)
+	if valSet.mixHash != nil { // mixHash is nil before Randao HF
+		newWeightedCouncil.mixHash = make([]byte, len(valSet.mixHash))
+		copy(newWeightedCouncil.mixHash, valSet.mixHash)
+	}
 
 	return &newWeightedCouncil
 }
diff --git a/node/cn/filters/api.go b/node/cn/filters/api.go
index 5d670be90c..451ef0705a 100644
--- a/node/cn/filters/api.go
+++ b/node/cn/filters/api.go
@@ -251,8 +251,10 @@ func RPCMarshalHeader(head *types.Header, rules params.Rules) map[string]interfa
 			result["baseFeePerGas"] = (*hexutil.Big)(head.BaseFee)
 		}
 	}
-	if rules.IsRandao {
+	if len(head.RandomReveal) > 0 {
 		result["randomReveal"] = hexutil.Bytes(head.RandomReveal)
+	}
+	if len(head.MixHash) > 0 {
 		result["mixhash"] = hexutil.Bytes(head.MixHash)
 	}