Save and Read State Diff Functions (#15438)

* bucket | configs | flag | cache

* save and read state diff

* remove named mutex

* remove named mutex

* save and read state diff

* fix linter

* set offset while creating cache

* save and read state diff

* fix linter

* rebase

* fix tests

* Update beacon-chain/db/kv/state_diff_helpers.go

Co-authored-by: Potuz <potuz@prysmaticlabs.com>

* adjustments to key

* remove lvl parameter when it's 0

* use named suffixes

---------

Co-authored-by: Potuz <potuz@prysmaticlabs.com>

beacon-chain/core/altair/upgrade.go

@@ -12,6 +12,47 @@ import (
 	"github.com/OffchainLabs/prysm/v6/proto/prysm/v1alpha1/attestation"
 )
 
+// ConvertToAltair converts a Phase 0 beacon state to an Altair beacon state.
+func ConvertToAltair(state state.BeaconState) (state.BeaconState, error) {
+	epoch := time.CurrentEpoch(state)
+
+	numValidators := state.NumValidators()
+	s := &ethpb.BeaconStateAltair{
+		GenesisTime:           state.GenesisTime(),
+		GenesisValidatorsRoot: state.GenesisValidatorsRoot(),
+		Slot:                  state.Slot(),
+		Fork: &ethpb.Fork{
+			PreviousVersion: state.Fork().CurrentVersion,
+			CurrentVersion:  params.BeaconConfig().AltairForkVersion,
+			Epoch:           epoch,
+		},
+		LatestBlockHeader:           state.LatestBlockHeader(),
+		BlockRoots:                  state.BlockRoots(),
+		StateRoots:                  state.StateRoots(),
+		HistoricalRoots:             state.HistoricalRoots(),
+		Eth1Data:                    state.Eth1Data(),
+		Eth1DataVotes:               state.Eth1DataVotes(),
+		Eth1DepositIndex:            state.Eth1DepositIndex(),
+		Validators:                  state.Validators(),
+		Balances:                    state.Balances(),
+		RandaoMixes:                 state.RandaoMixes(),
+		Slashings:                   state.Slashings(),
+		PreviousEpochParticipation:  make([]byte, numValidators),
+		CurrentEpochParticipation:   make([]byte, numValidators),
+		JustificationBits:           state.JustificationBits(),
+		PreviousJustifiedCheckpoint: state.PreviousJustifiedCheckpoint(),
+		CurrentJustifiedCheckpoint:  state.CurrentJustifiedCheckpoint(),
+		FinalizedCheckpoint:         state.FinalizedCheckpoint(),
+		InactivityScores:            make([]uint64, numValidators),
+	}
+
+	newState, err := state_native.InitializeFromProtoUnsafeAltair(s)
+	if err != nil {
+		return nil, err
+	}
+	return newState, nil
+}
+
 // UpgradeToAltair updates input state to return the version Altair state.
 //
 // Spec code:
@@ -64,39 +105,7 @@ import (
 //	post.next_sync_committee = get_next_sync_committee(post)
 //	return post
 func UpgradeToAltair(ctx context.Context, state state.BeaconState) (state.BeaconState, error) {
-	epoch := time.CurrentEpoch(state)
-
-	numValidators := state.NumValidators()
-	s := &ethpb.BeaconStateAltair{
-		GenesisTime:           state.GenesisTime(),
-		GenesisValidatorsRoot: state.GenesisValidatorsRoot(),
-		Slot:                  state.Slot(),
-		Fork: &ethpb.Fork{
-			PreviousVersion: state.Fork().CurrentVersion,
-			CurrentVersion:  params.BeaconConfig().AltairForkVersion,
-			Epoch:           epoch,
-		},
-		LatestBlockHeader:           state.LatestBlockHeader(),
-		BlockRoots:                  state.BlockRoots(),
-		StateRoots:                  state.StateRoots(),
-		HistoricalRoots:             state.HistoricalRoots(),
-		Eth1Data:                    state.Eth1Data(),
-		Eth1DataVotes:               state.Eth1DataVotes(),
-		Eth1DepositIndex:            state.Eth1DepositIndex(),
-		Validators:                  state.Validators(),
-		Balances:                    state.Balances(),
-		RandaoMixes:                 state.RandaoMixes(),
-		Slashings:                   state.Slashings(),
-		PreviousEpochParticipation:  make([]byte, numValidators),
-		CurrentEpochParticipation:   make([]byte, numValidators),
-		JustificationBits:           state.JustificationBits(),
-		PreviousJustifiedCheckpoint: state.PreviousJustifiedCheckpoint(),
-		CurrentJustifiedCheckpoint:  state.CurrentJustifiedCheckpoint(),
-		FinalizedCheckpoint:         state.FinalizedCheckpoint(),
-		InactivityScores:            make([]uint64, numValidators),
-	}
-
-	newState, err := state_native.InitializeFromProtoUnsafeAltair(s)
+	newState, err := ConvertToAltair(state)
 	if err != nil {
 		return nil, err
 	}

beacon-chain/core/electra/upgrade.go

@@ -15,6 +15,129 @@ import (
 	"github.com/pkg/errors"
 )
 
+// ConvertToElectra converts a Deneb beacon state to an Electra beacon state.
+func ConvertToElectra(beaconState state.BeaconState) (state.BeaconState, error) {
+	currentSyncCommittee, err := beaconState.CurrentSyncCommittee()
+	if err != nil {
+		return nil, err
+	}
+	nextSyncCommittee, err := beaconState.NextSyncCommittee()
+	if err != nil {
+		return nil, err
+	}
+	prevEpochParticipation, err := beaconState.PreviousEpochParticipation()
+	if err != nil {
+		return nil, err
+	}
+	currentEpochParticipation, err := beaconState.CurrentEpochParticipation()
+	if err != nil {
+		return nil, err
+	}
+	inactivityScores, err := beaconState.InactivityScores()
+	if err != nil {
+		return nil, err
+	}
+	payloadHeader, err := beaconState.LatestExecutionPayloadHeader()
+	if err != nil {
+		return nil, err
+	}
+	txRoot, err := payloadHeader.TransactionsRoot()
+	if err != nil {
+		return nil, err
+	}
+	wdRoot, err := payloadHeader.WithdrawalsRoot()
+	if err != nil {
+		return nil, err
+	}
+	wi, err := beaconState.NextWithdrawalIndex()
+	if err != nil {
+		return nil, err
+	}
+	vi, err := beaconState.NextWithdrawalValidatorIndex()
+	if err != nil {
+		return nil, err
+	}
+	summaries, err := beaconState.HistoricalSummaries()
+	if err != nil {
+		return nil, err
+	}
+	excessBlobGas, err := payloadHeader.ExcessBlobGas()
+	if err != nil {
+		return nil, err
+	}
+	blobGasUsed, err := payloadHeader.BlobGasUsed()
+	if err != nil {
+		return nil, err
+	}
+
+	s := &ethpb.BeaconStateElectra{
+		GenesisTime:           beaconState.GenesisTime(),
+		GenesisValidatorsRoot: beaconState.GenesisValidatorsRoot(),
+		Slot:                  beaconState.Slot(),
+		Fork: &ethpb.Fork{
+			PreviousVersion: beaconState.Fork().CurrentVersion,
+			CurrentVersion:  params.BeaconConfig().ElectraForkVersion,
+			Epoch:           time.CurrentEpoch(beaconState),
+		},
+		LatestBlockHeader:           beaconState.LatestBlockHeader(),
+		BlockRoots:                  beaconState.BlockRoots(),
+		StateRoots:                  beaconState.StateRoots(),
+		HistoricalRoots:             beaconState.HistoricalRoots(),
+		Eth1Data:                    beaconState.Eth1Data(),
+		Eth1DataVotes:               beaconState.Eth1DataVotes(),
+		Eth1DepositIndex:            beaconState.Eth1DepositIndex(),
+		Validators:                  beaconState.Validators(),
+		Balances:                    beaconState.Balances(),
+		RandaoMixes:                 beaconState.RandaoMixes(),
+		Slashings:                   beaconState.Slashings(),
+		PreviousEpochParticipation:  prevEpochParticipation,
+		CurrentEpochParticipation:   currentEpochParticipation,
+		JustificationBits:           beaconState.JustificationBits(),
+		PreviousJustifiedCheckpoint: beaconState.PreviousJustifiedCheckpoint(),
+		CurrentJustifiedCheckpoint:  beaconState.CurrentJustifiedCheckpoint(),
+		FinalizedCheckpoint:         beaconState.FinalizedCheckpoint(),
+		InactivityScores:            inactivityScores,
+		CurrentSyncCommittee:        currentSyncCommittee,
+		NextSyncCommittee:           nextSyncCommittee,
+		LatestExecutionPayloadHeader: &enginev1.ExecutionPayloadHeaderDeneb{
+			ParentHash:       payloadHeader.ParentHash(),
+			FeeRecipient:     payloadHeader.FeeRecipient(),
+			StateRoot:        payloadHeader.StateRoot(),
+			ReceiptsRoot:     payloadHeader.ReceiptsRoot(),
+			LogsBloom:        payloadHeader.LogsBloom(),
+			PrevRandao:       payloadHeader.PrevRandao(),
+			BlockNumber:      payloadHeader.BlockNumber(),
+			GasLimit:         payloadHeader.GasLimit(),
+			GasUsed:          payloadHeader.GasUsed(),
+			Timestamp:        payloadHeader.Timestamp(),
+			ExtraData:        payloadHeader.ExtraData(),
+			BaseFeePerGas:    payloadHeader.BaseFeePerGas(),
+			BlockHash:        payloadHeader.BlockHash(),
+			TransactionsRoot: txRoot,
+			WithdrawalsRoot:  wdRoot,
+			ExcessBlobGas:    excessBlobGas,
+			BlobGasUsed:      blobGasUsed,
+		},
+		NextWithdrawalIndex:          wi,
+		NextWithdrawalValidatorIndex: vi,
+		HistoricalSummaries:          summaries,
+
+		DepositRequestsStartIndex:  params.BeaconConfig().UnsetDepositRequestsStartIndex,
+		DepositBalanceToConsume:    0,
+		EarliestConsolidationEpoch: helpers.ActivationExitEpoch(slots.ToEpoch(beaconState.Slot())),
+		PendingDeposits:            make([]*ethpb.PendingDeposit, 0),
+		PendingPartialWithdrawals:  make([]*ethpb.PendingPartialWithdrawal, 0),
+		PendingConsolidations:      make([]*ethpb.PendingConsolidation, 0),
+	}
+
+	// need to cast the beaconState to use in helper functions
+	post, err := state_native.InitializeFromProtoUnsafeElectra(s)
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to initialize post electra beaconState")
+	}
+	return post, nil
+}
+
 // UpgradeToElectra updates inputs a generic state to return the version Electra state.
 //
 // nolint:dupword

beacon-chain/core/execution/BUILD.bazel

@@ -7,6 +7,7 @@ go_library(
     visibility = [
         "//beacon-chain:__subpackages__",
         "//cmd/prysmctl/testnet:__pkg__",
+        "//consensus-types/hdiff:__subpackages__",
         "//testing/spectest:__subpackages__",
         "//validator/client:__pkg__",
     ],

beacon-chain/db/kv/BUILD.bazel

@@ -25,6 +25,9 @@ go_library(
         "migration_state_validators.go",
         "schema.go",
         "state.go",
+        "state_diff.go",
+        "state_diff_cache.go",
+        "state_diff_helpers.go",
         "state_summary.go",
         "state_summary_cache.go",
         "utils.go",
@@ -44,6 +47,7 @@ go_library(
         "//config/fieldparams:go_default_library",
         "//config/params:go_default_library",
         "//consensus-types/blocks:go_default_library",
+        "//consensus-types/hdiff:go_default_library",
         "//consensus-types/interfaces:go_default_library",
         "//consensus-types/light-client:go_default_library",
         "//consensus-types/primitives:go_default_library",
@@ -51,6 +55,7 @@ go_library(
         "//encoding/bytesutil:go_default_library",
         "//encoding/ssz/detect:go_default_library",
         "//io/file:go_default_library",
+        "//math:go_default_library",
         "//monitoring/progress:go_default_library",
         "//monitoring/tracing:go_default_library",
         "//monitoring/tracing/trace:go_default_library",
@@ -94,6 +99,7 @@ go_test(
         "migration_archived_index_test.go",
         "migration_block_slot_index_test.go",
         "migration_state_validators_test.go",
+        "state_diff_test.go",
         "state_summary_test.go",
         "state_test.go",
         "utils_test.go",
@@ -116,6 +122,7 @@ go_test(
         "//consensus-types/light-client:go_default_library",
         "//consensus-types/primitives:go_default_library",
         "//encoding/bytesutil:go_default_library",
+        "//math:go_default_library",
         "//proto/dbval:go_default_library",
         "//proto/engine/v1:go_default_library",
         "//proto/prysm/v1alpha1:go_default_library",

beacon-chain/db/kv/kv.go

@@ -91,6 +91,7 @@ type Store struct {
 	blockCache          *ristretto.Cache[string, interfaces.ReadOnlySignedBeaconBlock]
 	validatorEntryCache *ristretto.Cache[[]byte, *ethpb.Validator]
 	stateSummaryCache   *stateSummaryCache
+	stateDiffCache      *stateDiffCache
 	ctx                 context.Context
 }
 
@@ -112,6 +113,7 @@ var Buckets = [][]byte{
 	lightClientUpdatesBucket,
 	lightClientBootstrapBucket,
 	lightClientSyncCommitteeBucket,
+	stateDiffBucket,
 	// Indices buckets.
 	blockSlotIndicesBucket,
 	stateSlotIndicesBucket,
@@ -182,6 +184,7 @@ func NewKVStore(ctx context.Context, dirPath string, opts ...KVStoreOption) (*St
 		blockCache:          blockCache,
 		validatorEntryCache: validatorCache,
 		stateSummaryCache:   newStateSummaryCache(),
+		stateDiffCache:      nil,
 		ctx:                 ctx,
 	}
 	for _, o := range opts {
@@ -200,6 +203,14 @@ func NewKVStore(ctx context.Context, dirPath string, opts ...KVStoreOption) (*St
 		return nil, err
 	}
 
+	if features.Get().EnableStateDiff {
+		sdCache, err := newStateDiffCache(kv)
+		if err != nil {
+			return nil, err
+		}
+		kv.stateDiffCache = sdCache
+	}
+
 	return kv, nil
 }
 

beacon-chain/db/kv/schema.go

@@ -16,6 +16,7 @@ var (
 	stateValidatorsBucket = []byte("state-validators")
 	feeRecipientBucket    = []byte("fee-recipient")
 	registrationBucket    = []byte("registration")
+	stateDiffBucket       = []byte("state-diff")
 
 	// Light Client Updates Bucket
 	lightClientUpdatesBucket       = []byte("light-client-updates")

beacon-chain/db/kv/state_diff.go

@@ -0,0 +1,232 @@
+package kv
+
+import (
+	"context"
+
+	"github.com/OffchainLabs/prysm/v6/beacon-chain/state"
+	"github.com/OffchainLabs/prysm/v6/config/params"
+	"github.com/OffchainLabs/prysm/v6/consensus-types/hdiff"
+	"github.com/OffchainLabs/prysm/v6/consensus-types/primitives"
+	"github.com/OffchainLabs/prysm/v6/monitoring/tracing/trace"
+	"github.com/pkg/errors"
+	bolt "go.etcd.io/bbolt"
+)
+
+const (
+	stateSuffix     = "_s"
+	validatorSuffix = "_v"
+	balancesSuffix  = "_b"
+)
+
+/*
+	We use a level-based approach to save state diffs. The levels are 0-6, where each level corresponds to an exponent of 2 (exponents[lvl]).
+	The data at level 0 is saved every 2**exponent[0] slots and always contains a full state snapshot that is used as a base for the delta saved at other levels.
+*/
+
+// saveStateByDiff takes a state and decides between saving a full state snapshot or a diff.
+func (s *Store) saveStateByDiff(ctx context.Context, st state.ReadOnlyBeaconState) error {
+	_, span := trace.StartSpan(ctx, "BeaconDB.saveStateByDiff")
+	defer span.End()
+
+	if st == nil {
+		return errors.New("state is nil")
+	}
+
+	slot := st.Slot()
+	offset := s.getOffset()
+	if uint64(slot) < offset {
+		return ErrSlotBeforeOffset
+	}
+
+	// Find the level to save the state.
+	lvl := computeLevel(offset, slot)
+	if lvl == -1 {
+		return nil
+	}
+
+	// Save full state if level is 0.
+	if lvl == 0 {
+		return s.saveFullSnapshot(st)
+	}
+
+	// Get anchor state to compute the diff from.
+	anchorState, err := s.getAnchorState(offset, lvl, slot)
+	if err != nil {
+		return err
+	}
+
+	err = s.saveHdiff(lvl, anchorState, st)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// stateByDiff retrieves the full state for a given slot.
+func (s *Store) stateByDiff(ctx context.Context, slot primitives.Slot) (state.BeaconState, error) {
+	offset := s.getOffset()
+	if uint64(slot) < offset {
+		return nil, ErrSlotBeforeOffset
+	}
+
+	snapshot, diffChain, err := s.getBaseAndDiffChain(offset, slot)
+	if err != nil {
+		return nil, err
+	}
+
+	for _, diff := range diffChain {
+		snapshot, err = hdiff.ApplyDiff(ctx, snapshot, diff)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	return snapshot, nil
+}
+
+// SaveHdiff computes the diff between the anchor state and the current state and saves it to the database.
+func (s *Store) saveHdiff(lvl int, anchor, st state.ReadOnlyBeaconState) error {
+	slot := uint64(st.Slot())
+	key := makeKey(lvl, slot)
+
+	diff, err := hdiff.Diff(anchor, st)
+	if err != nil {
+		return err
+	}
+
+	err = s.db.Update(func(tx *bolt.Tx) error {
+		bucket := tx.Bucket(stateDiffBucket)
+		if bucket == nil {
+			return bolt.ErrBucketNotFound
+		}
+		buf := append(key, stateSuffix...)
+		if err := bucket.Put(buf, diff.StateDiff); err != nil {
+			return err
+		}
+		buf = append(key, validatorSuffix...)
+		if err := bucket.Put(buf, diff.ValidatorDiffs); err != nil {
+			return err
+		}
+		buf = append(key, balancesSuffix...)
+		if err := bucket.Put(buf, diff.BalancesDiff); err != nil {
+			return err
+		}
+		return nil
+	})
+	if err != nil {
+		return err
+	}
+
+	// Save the full state to the cache (if not the last level).
+	if lvl != len(params.StateHierarchyExponents())-1 {
+		err = s.stateDiffCache.setAnchor(lvl, st)
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+// SaveFullSnapshot saves the full level 0 state snapshot to the database.
+func (s *Store) saveFullSnapshot(st state.ReadOnlyBeaconState) error {
+	slot := uint64(st.Slot())
+	key := makeKey(0, slot)
+	stateBytes, err := st.MarshalSSZ()
+	if err != nil {
+		return err
+	}
+	// add version key to value
+	enc, err := addKey(st.Version(), stateBytes)
+	if err != nil {
+		return err
+	}
+
+	err = s.db.Update(func(tx *bolt.Tx) error {
+		bucket := tx.Bucket(stateDiffBucket)
+		if bucket == nil {
+			return bolt.ErrBucketNotFound
+		}
+
+		if err := bucket.Put(key, enc); err != nil {
+			return err
+		}
+
+		return nil
+	})
+	if err != nil {
+		return err
+	}
+	// Save the full state to the cache, and invalidate other levels.
+	s.stateDiffCache.clearAnchors()
+	err = s.stateDiffCache.setAnchor(0, st)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func (s *Store) getDiff(lvl int, slot uint64) (hdiff.HdiffBytes, error) {
+	key := makeKey(lvl, slot)
+	var stateDiff []byte
+	var validatorDiff []byte
+	var balancesDiff []byte
+
+	err := s.db.View(func(tx *bolt.Tx) error {
+		bucket := tx.Bucket(stateDiffBucket)
+		if bucket == nil {
+			return bolt.ErrBucketNotFound
+		}
+		buf := append(key, stateSuffix...)
+		stateDiff = bucket.Get(buf)
+		if stateDiff == nil {
+			return errors.New("state diff not found")
+		}
+		buf = append(key, validatorSuffix...)
+		validatorDiff = bucket.Get(buf)
+		if validatorDiff == nil {
+			return errors.New("validator diff not found")
+		}
+		buf = append(key, balancesSuffix...)
+		balancesDiff = bucket.Get(buf)
+		if balancesDiff == nil {
+			return errors.New("balances diff not found")
+		}
+		return nil
+	})
+
+	if err != nil {
+		return hdiff.HdiffBytes{}, err
+	}
+
+	return hdiff.HdiffBytes{
+		StateDiff:      stateDiff,
+		ValidatorDiffs: validatorDiff,
+		BalancesDiff:   balancesDiff,
+	}, nil
+}
+
+func (s *Store) getFullSnapshot(slot uint64) (state.BeaconState, error) {
+	key := makeKey(0, slot)
+	var enc []byte
+
+	err := s.db.View(func(tx *bolt.Tx) error {
+		bucket := tx.Bucket(stateDiffBucket)
+		if bucket == nil {
+			return bolt.ErrBucketNotFound
+		}
+		enc = bucket.Get(key)
+		if enc == nil {
+			return errors.New("state not found")
+		}
+		return nil
+	})
+
+	if err != nil {
+		return nil, err
+	}
+
+	return s.decodeStateSnapshot(enc)
+}

beacon-chain/db/kv/state_diff_cache.go

@@ -0,0 +1,77 @@
+package kv
+
+import (
+	"encoding/binary"
+	"errors"
+	"sync"
+
+	"github.com/OffchainLabs/prysm/v6/beacon-chain/state"
+	"github.com/OffchainLabs/prysm/v6/config/params"
+	"go.etcd.io/bbolt"
+)
+
+type stateDiffCache struct {
+	sync.RWMutex
+	anchors []state.ReadOnlyBeaconState
+	offset  uint64
+}
+
+func newStateDiffCache(s *Store) (*stateDiffCache, error) {
+	var offset uint64
+
+	err := s.db.View(func(tx *bbolt.Tx) error {
+		bucket := tx.Bucket(stateDiffBucket)
+		if bucket == nil {
+			return bbolt.ErrBucketNotFound
+		}
+
+		offsetBytes := bucket.Get([]byte("offset"))
+		if offsetBytes == nil {
+			return errors.New("state diff cache: offset not found")
+		}
+		offset = binary.LittleEndian.Uint64(offsetBytes)
+		return nil
+	})
+	if err != nil {
+		return nil, err
+	}
+
+	return &stateDiffCache{
+		anchors: make([]state.ReadOnlyBeaconState, len(params.StateHierarchyExponents())),
+		offset:  offset,
+	}, nil
+}
+
+func (c *stateDiffCache) getAnchor(level int) state.ReadOnlyBeaconState {
+	c.RLock()
+	defer c.RUnlock()
+	return c.anchors[level]
+}
+
+func (c *stateDiffCache) setAnchor(level int, anchor state.ReadOnlyBeaconState) error {
+	c.Lock()
+	defer c.Unlock()
+	if level >= len(c.anchors) || level < 0 {
+		return errors.New("state diff cache: anchor level out of range")
+	}
+	c.anchors[level] = anchor
+	return nil
+}
+
+func (c *stateDiffCache) getOffset() uint64 {
+	c.RLock()
+	defer c.RUnlock()
+	return c.offset
+}
+
+func (c *stateDiffCache) setOffset(offset uint64) {
+	c.Lock()
+	defer c.Unlock()
+	c.offset = offset
+}
+
+func (c *stateDiffCache) clearAnchors() {
+	c.Lock()
+	defer c.Unlock()
+	c.anchors = make([]state.ReadOnlyBeaconState, len(params.StateHierarchyExponents()))
+}

beacon-chain/db/kv/state_diff_helpers.go

@@ -0,0 +1,234 @@
+package kv
+
+import (
+	"context"
+	"encoding/binary"
+	"errors"
+	"fmt"
+
+	"github.com/OffchainLabs/prysm/v6/beacon-chain/state"
+	state_native "github.com/OffchainLabs/prysm/v6/beacon-chain/state/state-native"
+	"github.com/OffchainLabs/prysm/v6/config/params"
+	"github.com/OffchainLabs/prysm/v6/consensus-types/hdiff"
+	"github.com/OffchainLabs/prysm/v6/consensus-types/primitives"
+	"github.com/OffchainLabs/prysm/v6/math"
+	ethpb "github.com/OffchainLabs/prysm/v6/proto/prysm/v1alpha1"
+	"github.com/OffchainLabs/prysm/v6/runtime/version"
+	"go.etcd.io/bbolt"
+)
+
+var (
+	offsetKey           = []byte("offset")
+	ErrSlotBeforeOffset = errors.New("slot is before root offset")
+)
+
+func makeKey(level int, slot uint64) []byte {
+	buf := make([]byte, 16)
+	buf[0] = byte(level)
+	binary.LittleEndian.PutUint64(buf[1:], slot)
+	return buf
+}
+
+func (s *Store) getAnchorState(offset uint64, lvl int, slot primitives.Slot) (anchor state.ReadOnlyBeaconState, err error) {
+	if lvl <= 0 || lvl >= len(params.StateHierarchyExponents()) {
+		return nil, errors.New("invalid value for level")
+	}
+
+	relSlot := uint64(slot) - offset
+	prevExp := params.StateHierarchyExponents()[lvl-1]
+	span := math.PowerOf2(prevExp)
+	anchorSlot := primitives.Slot((relSlot / span * span) + offset)
+
+	// anchorLvl can be [0, lvl-1]
+	anchorLvl := computeLevel(offset, anchorSlot)
+	if anchorLvl == -1 {
+		return nil, errors.New("could not compute anchor level")
+	}
+
+	// Check if we have the anchor in cache.
+	anchor = s.stateDiffCache.getAnchor(anchorLvl)
+	if anchor != nil {
+		return anchor, nil
+	}
+
+	// If not, load it from the database.
+	anchor, err = s.stateByDiff(context.Background(), anchorSlot)
+	if err != nil {
+		return nil, err
+	}
+
+	// Save it in the cache.
+	err = s.stateDiffCache.setAnchor(anchorLvl, anchor)
+	if err != nil {
+		return nil, err
+	}
+	return anchor, nil
+}
+
+// computeLevel computes the level in the diff tree. Returns -1 in case slot should not be in tree.
+func computeLevel(offset uint64, slot primitives.Slot) int {
+	rel := uint64(slot) - offset
+	for i, exp := range params.StateHierarchyExponents() {
+		span := math.PowerOf2(exp)
+		if rel%span == 0 {
+			return i
+		}
+	}
+	// If rel isn’t on any of the boundaries, we should ignore saving it.
+	return -1
+}
+
+func (s *Store) setOffset(slot primitives.Slot) error {
+	err := s.db.Update(func(tx *bbolt.Tx) error {
+		bucket := tx.Bucket(stateDiffBucket)
+		if bucket == nil {
+			return bbolt.ErrBucketNotFound
+		}
+
+		offsetBytes := bucket.Get(offsetKey)
+		if offsetBytes != nil {
+			return fmt.Errorf("offset already set to %d", binary.LittleEndian.Uint64(offsetBytes))
+		}
+
+		offsetBytes = make([]byte, 8)
+		binary.LittleEndian.PutUint64(offsetBytes, uint64(slot))
+		if err := bucket.Put(offsetKey, offsetBytes); err != nil {
+			return err
+		}
+		return nil
+	})
+	if err != nil {
+		return err
+	}
+
+	// Save the offset in the cache.
+	s.stateDiffCache.setOffset(uint64(slot))
+	return nil
+}
+
+func (s *Store) getOffset() uint64 {
+	return s.stateDiffCache.getOffset()
+}
+
+func keyForSnapshot(v int) []byte {
+	switch v {
+	case version.Fulu:
+		return fuluKey
+	case version.Electra:
+		return ElectraKey
+	case version.Deneb:
+		return denebKey
+	case version.Capella:
+		return capellaKey
+	case version.Bellatrix:
+		return bellatrixKey
+	case version.Altair:
+		return altairKey
+	default:
+		// Phase0
+		return []byte{}
+	}
+}
+
+func addKey(v int, bytes []byte) ([]byte, error) {
+	key := keyForSnapshot(v)
+	enc := make([]byte, len(key)+len(bytes))
+	copy(enc, key)
+	copy(enc[len(key):], bytes)
+	return enc, nil
+}
+
+func (s *Store) decodeStateSnapshot(enc []byte) (state.BeaconState, error) {
+	switch {
+	case hasFuluKey(enc):
+		var fuluState ethpb.BeaconStateFulu
+		if err := fuluState.UnmarshalSSZ(enc[len(ElectraKey):]); err != nil {
+			return nil, err
+		}
+		return state_native.InitializeFromProtoUnsafeFulu(&fuluState)
+	case HasElectraKey(enc):
+		var electraState ethpb.BeaconStateElectra
+		if err := electraState.UnmarshalSSZ(enc[len(ElectraKey):]); err != nil {
+			return nil, err
+		}
+		return state_native.InitializeFromProtoUnsafeElectra(&electraState)
+	case hasDenebKey(enc):
+		var denebState ethpb.BeaconStateDeneb
+		if err := denebState.UnmarshalSSZ(enc[len(denebKey):]); err != nil {
+			return nil, err
+		}
+		return state_native.InitializeFromProtoUnsafeDeneb(&denebState)
+	case hasCapellaKey(enc):
+		var capellaState ethpb.BeaconStateCapella
+		if err := capellaState.UnmarshalSSZ(enc[len(capellaKey):]); err != nil {
+			return nil, err
+		}
+		return state_native.InitializeFromProtoUnsafeCapella(&capellaState)
+	case hasBellatrixKey(enc):
+		var bellatrixState ethpb.BeaconStateBellatrix
+		if err := bellatrixState.UnmarshalSSZ(enc[len(bellatrixKey):]); err != nil {
+			return nil, err
+		}
+		return state_native.InitializeFromProtoUnsafeBellatrix(&bellatrixState)
+	case hasAltairKey(enc):
+		var altairState ethpb.BeaconStateAltair
+		if err := altairState.UnmarshalSSZ(enc[len(altairKey):]); err != nil {
+			return nil, err
+		}
+		return state_native.InitializeFromProtoUnsafeAltair(&altairState)
+	default:
+		var phase0State ethpb.BeaconState
+		if err := phase0State.UnmarshalSSZ(enc); err != nil {
+			return nil, err
+		}
+		return state_native.InitializeFromProtoUnsafePhase0(&phase0State)
+	}
+}
+
+func (s *Store) getBaseAndDiffChain(offset uint64, slot primitives.Slot) (state.BeaconState, []hdiff.HdiffBytes, error) {
+	rel := uint64(slot) - offset
+	lvl := computeLevel(offset, slot)
+	if lvl == -1 {
+		return nil, nil, errors.New("slot not in tree")
+	}
+
+	exponents := params.StateHierarchyExponents()
+
+	baseSpan := math.PowerOf2(exponents[0])
+	baseAnchorSlot := (rel / baseSpan * baseSpan) + offset
+
+	var diffChainIndices []uint64
+	for i := 1; i <= lvl; i++ {
+		span := math.PowerOf2(exponents[i])
+		diffSlot := rel / span * span
+		if diffSlot == baseAnchorSlot {
+			continue
+		}
+		diffChainIndices = appendUnique(diffChainIndices, diffSlot+offset)
+	}
+
+	baseSnapshot, err := s.getFullSnapshot(baseAnchorSlot)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	diffChain := make([]hdiff.HdiffBytes, 0, len(diffChainIndices))
+	for _, diffSlot := range diffChainIndices {
+		diff, err := s.getDiff(computeLevel(offset, primitives.Slot(diffSlot)), diffSlot)
+		if err != nil {
+			return nil, nil, err
+		}
+		diffChain = append(diffChain, diff)
+	}
+
+	return baseSnapshot, diffChain, nil
+}
+
+func appendUnique(s []uint64, v uint64) []uint64 {
+	for _, x := range s {
+		if x == v {
+			return s
+		}
+	}
+	return append(s, v)
+}

beacon-chain/db/kv/state_diff_test.go

@@ -0,0 +1,577 @@
+package kv
+
+import (
+	"context"
+	"encoding/binary"
+	"fmt"
+	"math/rand"
+	"testing"
+
+	"github.com/OffchainLabs/prysm/v6/beacon-chain/state"
+	"github.com/OffchainLabs/prysm/v6/config/params"
+	"github.com/OffchainLabs/prysm/v6/consensus-types/primitives"
+	"github.com/OffchainLabs/prysm/v6/math"
+	ethpb "github.com/OffchainLabs/prysm/v6/proto/prysm/v1alpha1"
+	"github.com/OffchainLabs/prysm/v6/runtime/version"
+	"github.com/OffchainLabs/prysm/v6/testing/require"
+	"github.com/OffchainLabs/prysm/v6/testing/util"
+	"go.etcd.io/bbolt"
+)
+
+func TestStateDiff_LoadOrInitOffset(t *testing.T) {
+	db := setupDB(t)
+	err := setOffsetInDB(db, 10)
+	require.NoError(t, err)
+	offset := db.getOffset()
+	require.Equal(t, uint64(10), offset)
+
+	err = db.setOffset(10)
+	require.ErrorContains(t, "offset already set", err)
+	offset = db.getOffset()
+	require.Equal(t, uint64(10), offset)
+}
+
+func TestStateDiff_ComputeLevel(t *testing.T) {
+	db := setupDB(t)
+
+	err := setOffsetInDB(db, 0)
+	require.NoError(t, err)
+
+	offset := db.getOffset()
+
+	// 2 ** 21
+	lvl := computeLevel(offset, primitives.Slot(math.PowerOf2(21)))
+	require.Equal(t, 0, lvl)
+
+	// 2 ** 21 * 3
+	lvl = computeLevel(offset, primitives.Slot(math.PowerOf2(21)*3))
+	require.Equal(t, 0, lvl)
+
+	// 2 ** 18
+	lvl = computeLevel(offset, primitives.Slot(math.PowerOf2(18)))
+	require.Equal(t, 1, lvl)
+
+	// 2 ** 18 * 3
+	lvl = computeLevel(offset, primitives.Slot(math.PowerOf2(18)*3))
+	require.Equal(t, 1, lvl)
+
+	// 2 ** 16
+	lvl = computeLevel(offset, primitives.Slot(math.PowerOf2(16)))
+	require.Equal(t, 2, lvl)
+
+	// 2 ** 16 * 3
+	lvl = computeLevel(offset, primitives.Slot(math.PowerOf2(16)*3))
+	require.Equal(t, 2, lvl)
+
+	// 2 ** 13
+	lvl = computeLevel(offset, primitives.Slot(math.PowerOf2(13)))
+	require.Equal(t, 3, lvl)
+
+	// 2 ** 13 * 3
+	lvl = computeLevel(offset, primitives.Slot(math.PowerOf2(13)*3))
+	require.Equal(t, 3, lvl)
+
+	// 2 ** 11
+	lvl = computeLevel(offset, primitives.Slot(math.PowerOf2(11)))
+	require.Equal(t, 4, lvl)
+
+	// 2 ** 11 * 3
+	lvl = computeLevel(offset, primitives.Slot(math.PowerOf2(11)*3))
+	require.Equal(t, 4, lvl)
+
+	// 2 ** 9
+	lvl = computeLevel(offset, primitives.Slot(math.PowerOf2(9)))
+	require.Equal(t, 5, lvl)
+
+	// 2 ** 9 * 3
+	lvl = computeLevel(offset, primitives.Slot(math.PowerOf2(9)*3))
+	require.Equal(t, 5, lvl)
+
+	// 2 ** 5
+	lvl = computeLevel(offset, primitives.Slot(math.PowerOf2(5)))
+	require.Equal(t, 6, lvl)
+
+	// 2 ** 5 * 3
+	lvl = computeLevel(offset, primitives.Slot(math.PowerOf2(5)*3))
+	require.Equal(t, 6, lvl)
+
+	// 2 ** 7
+	lvl = computeLevel(offset, primitives.Slot(math.PowerOf2(7)))
+	require.Equal(t, 6, lvl)
+
+	// 2 ** 5 + 1
+	lvl = computeLevel(offset, primitives.Slot(math.PowerOf2(5)+1))
+	require.Equal(t, -1, lvl)
+
+	// 2 ** 5 + 16
+	lvl = computeLevel(offset, primitives.Slot(math.PowerOf2(5)+16))
+	require.Equal(t, -1, lvl)
+
+	// 2 ** 5 + 32
+	lvl = computeLevel(offset, primitives.Slot(math.PowerOf2(5)+32))
+	require.Equal(t, 6, lvl)
+
+}
+
+func TestStateDiff_SaveFullSnapshot(t *testing.T) {
+	// test for every version
+	for v := 0; v < 6; v++ {
+		t.Run(version.String(v), func(t *testing.T) {
+			db := setupDB(t)
+
+			// Create state with slot 0
+			st, enc := createState(t, 0, v)
+
+			err := setOffsetInDB(db, 0)
+			require.NoError(t, err)
+
+			err = db.saveStateByDiff(context.Background(), st)
+			require.NoError(t, err)
+
+			err = db.db.View(func(tx *bbolt.Tx) error {
+				bucket := tx.Bucket(stateDiffBucket)
+				if bucket == nil {
+					return bbolt.ErrBucketNotFound
+				}
+				s := bucket.Get(makeKey(0, uint64(0)))
+				if s == nil {
+					return bbolt.ErrIncompatibleValue
+				}
+				require.DeepSSZEqual(t, enc, s)
+				return nil
+			})
+			require.NoError(t, err)
+		})
+	}
+}
+
+func TestStateDiff_SaveAndReadFullSnapshot(t *testing.T) {
+	// test for every version
+	for v := 0; v < 6; v++ {
+		t.Run(version.String(v), func(t *testing.T) {
+			db := setupDB(t)
+
+			st, _ := createState(t, 0, v)
+
+			err := setOffsetInDB(db, 0)
+			require.NoError(t, err)
+
+			err = db.saveStateByDiff(context.Background(), st)
+			require.NoError(t, err)
+
+			readSt, err := db.stateByDiff(context.Background(), 0)
+			require.NoError(t, err)
+			require.NotNil(t, readSt)
+
+			stSSZ, err := st.MarshalSSZ()
+			require.NoError(t, err)
+			readStSSZ, err := readSt.MarshalSSZ()
+			require.NoError(t, err)
+			require.DeepSSZEqual(t, stSSZ, readStSSZ)
+		})
+	}
+}
+
+func TestStateDiff_SaveDiff(t *testing.T) {
+	// test for every version
+	for v := 0; v < 6; v++ {
+		t.Run(version.String(v), func(t *testing.T) {
+			db := setupDB(t)
+
+			// Create state with slot 2**21
+			slot := primitives.Slot(math.PowerOf2(21))
+			st, enc := createState(t, slot, v)
+
+			err := setOffsetInDB(db, uint64(slot))
+			require.NoError(t, err)
+
+			err = db.saveStateByDiff(context.Background(), st)
+			require.NoError(t, err)
+
+			err = db.db.View(func(tx *bbolt.Tx) error {
+				bucket := tx.Bucket(stateDiffBucket)
+				if bucket == nil {
+					return bbolt.ErrBucketNotFound
+				}
+				s := bucket.Get(makeKey(0, uint64(slot)))
+				if s == nil {
+					return bbolt.ErrIncompatibleValue
+				}
+				require.DeepSSZEqual(t, enc, s)
+				return nil
+			})
+			require.NoError(t, err)
+
+			// create state with slot 2**18 (+2**21)
+			slot = primitives.Slot(math.PowerOf2(18) + math.PowerOf2(21))
+			st, _ = createState(t, slot, v)
+
+			err = db.saveStateByDiff(context.Background(), st)
+			require.NoError(t, err)
+
+			key := makeKey(1, uint64(slot))
+			err = db.db.View(func(tx *bbolt.Tx) error {
+				bucket := tx.Bucket(stateDiffBucket)
+				if bucket == nil {
+					return bbolt.ErrBucketNotFound
+				}
+				buf := append(key, "_s"...)
+				s := bucket.Get(buf)
+				if s == nil {
+					return bbolt.ErrIncompatibleValue
+				}
+				buf = append(key, "_v"...)
+				v := bucket.Get(buf)
+				if v == nil {
+					return bbolt.ErrIncompatibleValue
+				}
+				buf = append(key, "_b"...)
+				b := bucket.Get(buf)
+				if b == nil {
+					return bbolt.ErrIncompatibleValue
+				}
+				return nil
+			})
+			require.NoError(t, err)
+		})
+	}
+}
+
+func TestStateDiff_SaveAndReadDiff(t *testing.T) {
+	// test for every version
+	for v := 0; v < 6; v++ {
+		t.Run(version.String(v), func(t *testing.T) {
+			db := setupDB(t)
+
+			st, _ := createState(t, 0, v)
+
+			err := setOffsetInDB(db, 0)
+			require.NoError(t, err)
+
+			err = db.saveStateByDiff(context.Background(), st)
+			require.NoError(t, err)
+
+			slot := primitives.Slot(math.PowerOf2(5))
+			st, _ = createState(t, slot, v)
+
+			err = db.saveStateByDiff(context.Background(), st)
+			require.NoError(t, err)
+
+			readSt, err := db.stateByDiff(context.Background(), slot)
+			require.NoError(t, err)
+			require.NotNil(t, readSt)
+
+			stSSZ, err := st.MarshalSSZ()
+			require.NoError(t, err)
+			readStSSZ, err := readSt.MarshalSSZ()
+			require.NoError(t, err)
+			require.DeepSSZEqual(t, stSSZ, readStSSZ)
+		})
+	}
+}
+
+func TestStateDiff_SaveAndReadDiff_MultipleLevels(t *testing.T) {
+	// test for every version
+	for v := 0; v < 6; v++ {
+		t.Run(version.String(v), func(t *testing.T) {
+			db := setupDB(t)
+
+			st, _ := createState(t, 0, v)
+
+			err := setOffsetInDB(db, 0)
+			require.NoError(t, err)
+
+			err = db.saveStateByDiff(context.Background(), st)
+			require.NoError(t, err)
+
+			slot := primitives.Slot(math.PowerOf2(11))
+			st, _ = createState(t, slot, v)
+
+			err = db.saveStateByDiff(context.Background(), st)
+			require.NoError(t, err)
+
+			readSt, err := db.stateByDiff(context.Background(), slot)
+			require.NoError(t, err)
+			require.NotNil(t, readSt)
+
+			stSSZ, err := st.MarshalSSZ()
+			require.NoError(t, err)
+			readStSSZ, err := readSt.MarshalSSZ()
+			require.NoError(t, err)
+			require.DeepSSZEqual(t, stSSZ, readStSSZ)
+
+			slot = primitives.Slot(math.PowerOf2(11) + math.PowerOf2(9))
+			st, _ = createState(t, slot, v)
+
+			err = db.saveStateByDiff(context.Background(), st)
+			require.NoError(t, err)
+
+			readSt, err = db.stateByDiff(context.Background(), slot)
+			require.NoError(t, err)
+			require.NotNil(t, readSt)
+
+			stSSZ, err = st.MarshalSSZ()
+			require.NoError(t, err)
+			readStSSZ, err = readSt.MarshalSSZ()
+			require.NoError(t, err)
+			require.DeepSSZEqual(t, stSSZ, readStSSZ)
+
+			slot = primitives.Slot(math.PowerOf2(11) + math.PowerOf2(9) + math.PowerOf2(5))
+			st, _ = createState(t, slot, v)
+
+			err = db.saveStateByDiff(context.Background(), st)
+			require.NoError(t, err)
+
+			readSt, err = db.stateByDiff(context.Background(), slot)
+			require.NoError(t, err)
+			require.NotNil(t, readSt)
+
+			stSSZ, err = st.MarshalSSZ()
+			require.NoError(t, err)
+			readStSSZ, err = readSt.MarshalSSZ()
+			require.NoError(t, err)
+			require.DeepSSZEqual(t, stSSZ, readStSSZ)
+		})
+	}
+}
+
+func TestStateDiff_SaveAndReadDiffForkTransition(t *testing.T) {
+	// test for every version
+	for v := 0; v < 5; v++ {
+		t.Run(version.String(v), func(t *testing.T) {
+			db := setupDB(t)
+
+			st, _ := createState(t, 0, v)
+
+			err := setOffsetInDB(db, 0)
+			require.NoError(t, err)
+
+			err = db.saveStateByDiff(context.Background(), st)
+			require.NoError(t, err)
+
+			slot := primitives.Slot(math.PowerOf2(5))
+			st, _ = createState(t, slot, v+1)
+
+			err = db.saveStateByDiff(context.Background(), st)
+			require.NoError(t, err)
+
+			readSt, err := db.stateByDiff(context.Background(), slot)
+			require.NoError(t, err)
+			require.NotNil(t, readSt)
+
+			stSSZ, err := st.MarshalSSZ()
+			require.NoError(t, err)
+			readStSSZ, err := readSt.MarshalSSZ()
+			require.NoError(t, err)
+			require.DeepSSZEqual(t, stSSZ, readStSSZ)
+		})
+	}
+}
+
+func TestStateDiff_OffsetCache(t *testing.T) {
+	// test for slot numbers 0 and 1 for every version
+	for slotNum := 0; slotNum < 2; slotNum++ {
+		// test for every version
+		for v := 0; v < 6; v++ {
+			t.Run(fmt.Sprintf("slotNum=%d,%s", slotNum, version.String(v)), func(t *testing.T) {
+				db := setupDB(t)
+
+				slot := primitives.Slot(slotNum)
+				err := setOffsetInDB(db, uint64(slot))
+				require.NoError(t, err)
+				st, _ := createState(t, slot, v)
+				err = db.saveStateByDiff(context.Background(), st)
+				require.NoError(t, err)
+
+				offset := db.stateDiffCache.getOffset()
+				require.Equal(t, uint64(slotNum), offset)
+
+				slot2 := primitives.Slot(uint64(slotNum) + math.PowerOf2(params.StateHierarchyExponents()[0]))
+				st2, _ := createState(t, slot2, v)
+				err = db.saveStateByDiff(context.Background(), st2)
+				require.NoError(t, err)
+
+				offset = db.stateDiffCache.getOffset()
+				require.Equal(t, uint64(slot), offset)
+			})
+		}
+	}
+}
+
+func TestStateDiff_AnchorCache(t *testing.T) {
+	// test for every version
+	for v := 0; v < 6; v++ {
+		t.Run(version.String(v), func(t *testing.T) {
+			exponents := params.StateHierarchyExponents()
+			localCache := make([]state.ReadOnlyBeaconState, len(exponents)-1)
+			db := setupDB(t)
+			err := setOffsetInDB(db, 0) // lvl 0
+			require.NoError(t, err)
+
+			// at first the cache should be empty
+			for i := 0; i < len(params.StateHierarchyExponents()); i++ {
+				anchor := db.stateDiffCache.getAnchor(i)
+				require.IsNil(t, anchor)
+			}
+
+			// add level 0
+			slot := primitives.Slot(0) // offset 0 is already set
+			st, _ := createState(t, slot, v)
+			err = db.saveStateByDiff(context.Background(), st)
+			require.NoError(t, err)
+			localCache[0] = st
+
+			// level 0 should be the same
+			require.DeepEqual(t, localCache[0], db.stateDiffCache.getAnchor(0))
+
+			// rest of the cache should be nil
+			for i := 1; i < len(exponents)-1; i++ {
+				require.IsNil(t, db.stateDiffCache.getAnchor(i))
+			}
+
+			// skip last level as it does not get cached
+			for i := len(exponents) - 2; i > 0; i-- {
+				slot = primitives.Slot(math.PowerOf2(exponents[i]))
+				st, _ := createState(t, slot, v)
+				err = db.saveStateByDiff(context.Background(), st)
+				require.NoError(t, err)
+				localCache[i] = st
+
+				// anchor cache must match local cache
+				for i := 0; i < len(exponents)-1; i++ {
+					if localCache[i] == nil {
+						require.IsNil(t, db.stateDiffCache.getAnchor(i))
+						continue
+					}
+					localSSZ, err := localCache[i].MarshalSSZ()
+					require.NoError(t, err)
+					anchorSSZ, err := db.stateDiffCache.getAnchor(i).MarshalSSZ()
+					require.NoError(t, err)
+					require.DeepSSZEqual(t, localSSZ, anchorSSZ)
+				}
+			}
+
+			// moving to a new tree should invalidate the cache except for level 0
+			twoTo21 := math.PowerOf2(21)
+			slot = primitives.Slot(twoTo21)
+			st, _ = createState(t, slot, v)
+			err = db.saveStateByDiff(context.Background(), st)
+			require.NoError(t, err)
+			localCache = make([]state.ReadOnlyBeaconState, len(exponents)-1)
+			localCache[0] = st
+
+			// level 0 should be the same
+			require.DeepEqual(t, localCache[0], db.stateDiffCache.getAnchor(0))
+
+			// rest of the cache should be nil
+			for i := 1; i < len(exponents)-1; i++ {
+				require.IsNil(t, db.stateDiffCache.getAnchor(i))
+			}
+		})
+	}
+}
+
+func createState(t *testing.T, slot primitives.Slot, v int) (state.ReadOnlyBeaconState, []byte) {
+	p := params.BeaconConfig()
+	var st state.BeaconState
+	var err error
+	switch v {
+	case version.Altair:
+		st, err = util.NewBeaconStateAltair()
+		require.NoError(t, err)
+		err = st.SetFork(&ethpb.Fork{
+			PreviousVersion: p.GenesisForkVersion,
+			CurrentVersion:  p.AltairForkVersion,
+			Epoch:           p.AltairForkEpoch,
+		})
+		require.NoError(t, err)
+	case version.Bellatrix:
+		st, err = util.NewBeaconStateBellatrix()
+		require.NoError(t, err)
+		err = st.SetFork(&ethpb.Fork{
+			PreviousVersion: p.AltairForkVersion,
+			CurrentVersion:  p.BellatrixForkVersion,
+			Epoch:           p.BellatrixForkEpoch,
+		})
+		require.NoError(t, err)
+	case version.Capella:
+		st, err = util.NewBeaconStateCapella()
+		require.NoError(t, err)
+		err = st.SetFork(&ethpb.Fork{
+			PreviousVersion: p.BellatrixForkVersion,
+			CurrentVersion:  p.CapellaForkVersion,
+			Epoch:           p.CapellaForkEpoch,
+		})
+		require.NoError(t, err)
+	case version.Deneb:
+		st, err = util.NewBeaconStateDeneb()
+		require.NoError(t, err)
+		err = st.SetFork(&ethpb.Fork{
+			PreviousVersion: p.CapellaForkVersion,
+			CurrentVersion:  p.DenebForkVersion,
+			Epoch:           p.DenebForkEpoch,
+		})
+		require.NoError(t, err)
+	case version.Electra:
+		st, err = util.NewBeaconStateElectra()
+		require.NoError(t, err)
+		err = st.SetFork(&ethpb.Fork{
+			PreviousVersion: p.DenebForkVersion,
+			CurrentVersion:  p.ElectraForkVersion,
+			Epoch:           p.ElectraForkEpoch,
+		})
+		require.NoError(t, err)
+	default:
+		st, err = util.NewBeaconState()
+		require.NoError(t, err)
+		err = st.SetFork(&ethpb.Fork{
+			PreviousVersion: p.GenesisForkVersion,
+			CurrentVersion:  p.GenesisForkVersion,
+			Epoch:           0,
+		})
+		require.NoError(t, err)
+	}
+
+	err = st.SetSlot(slot)
+	require.NoError(t, err)
+	slashings := make([]uint64, 8192)
+	slashings[0] = uint64(rand.Intn(10))
+	err = st.SetSlashings(slashings)
+	require.NoError(t, err)
+	stssz, err := st.MarshalSSZ()
+	require.NoError(t, err)
+	enc, err := addKey(v, stssz)
+	require.NoError(t, err)
+	return st, enc
+}
+
+func setOffsetInDB(s *Store, offset uint64) error {
+	err := s.db.Update(func(tx *bbolt.Tx) error {
+		bucket := tx.Bucket(stateDiffBucket)
+		if bucket == nil {
+			return bbolt.ErrBucketNotFound
+		}
+
+		offsetBytes := bucket.Get(offsetKey)
+		if offsetBytes != nil {
+			return fmt.Errorf("offset already set to %d", binary.LittleEndian.Uint64(offsetBytes))
+		}
+
+		offsetBytes = make([]byte, 8)
+		binary.LittleEndian.PutUint64(offsetBytes, offset)
+		if err := bucket.Put(offsetKey, offsetBytes); err != nil {
+			return err
+		}
+		return nil
+	})
+	if err != nil {
+		return err
+	}
+
+	sdCache, err := newStateDiffCache(s)
+	if err != nil {
+		return err
+	}
+	s.stateDiffCache = sdCache
+	return nil
+}

beacon-chain/state/interfaces.go

@@ -264,6 +264,8 @@ type WriteOnlyEth1Data interface {
 	AppendEth1DataVotes(val *ethpb.Eth1Data) error
 	SetEth1DepositIndex(val uint64) error
 	ExitEpochAndUpdateChurn(exitBalance primitives.Gwei) (primitives.Epoch, error)
+	SetExitBalanceToConsume(val primitives.Gwei) error
+	SetEarliestExitEpoch(val primitives.Epoch) error
 }
 
 // WriteOnlyValidators defines a struct which only has write access to validators methods.
@@ -331,6 +333,7 @@ type WriteOnlyWithdrawals interface {
 	DequeuePendingPartialWithdrawals(num uint64) error
 	SetNextWithdrawalIndex(i uint64) error
 	SetNextWithdrawalValidatorIndex(i primitives.ValidatorIndex) error
+	SetPendingPartialWithdrawals(val []*ethpb.PendingPartialWithdrawal) error
 }
 
 type WriteOnlyConsolidations interface {

beacon-chain/state/state-native/setters_churn.go

@@ -75,3 +75,33 @@ func (b *BeaconState) ExitEpochAndUpdateChurn(exitBalance primitives.Gwei) (prim
 
 	return b.earliestExitEpoch, nil
 }
+
+// SetExitBalanceToConsume sets the exit balance to consume. This method mutates the state.
+func (b *BeaconState) SetExitBalanceToConsume(exitBalanceToConsume primitives.Gwei) error {
+	if b.version < version.Electra {
+		return errNotSupported("SetExitBalanceToConsume", b.version)
+	}
+
+	b.lock.Lock()
+	defer b.lock.Unlock()
+
+	b.exitBalanceToConsume = exitBalanceToConsume
+	b.markFieldAsDirty(types.ExitBalanceToConsume)
+
+	return nil
+}
+
+// SetEarliestExitEpoch sets the earliest exit epoch. This method mutates the state.
+func (b *BeaconState) SetEarliestExitEpoch(earliestExitEpoch primitives.Epoch) error {
+	if b.version < version.Electra {
+		return errNotSupported("SetEarliestExitEpoch", b.version)
+	}
+
+	b.lock.Lock()
+	defer b.lock.Unlock()
+
+	b.earliestExitEpoch = earliestExitEpoch
+	b.markFieldAsDirty(types.EarliestExitEpoch)
+
+	return nil
+}

beacon-chain/state/state-native/setters_withdrawal.go

@@ -100,3 +100,22 @@ func (b *BeaconState) DequeuePendingPartialWithdrawals(n uint64) error {
 
 	return nil
 }
+
+// SetPendingPartialWithdrawals sets the pending partial withdrawals. This method mutates the state.
+func (b *BeaconState) SetPendingPartialWithdrawals(pendingPartialWithdrawals []*eth.PendingPartialWithdrawal) error {
+	if b.version < version.Electra {
+		return errNotSupported("SetPendingPartialWithdrawals", b.version)
+	}
+
+	b.lock.Lock()
+	defer b.lock.Unlock()
+
+	if pendingPartialWithdrawals == nil {
+		return errors.New("cannot set nil pending partial withdrawals")
+	}
+
+	b.pendingPartialWithdrawals = pendingPartialWithdrawals
+	b.markFieldAsDirty(types.PendingPartialWithdrawals)
+
+	return nil
+}

changelog/potuz_hdiff_diff_type.md

@@ -0,0 +1,3 @@
+### Added
+
+- Add native state diff type and marshalling functions

config/features/config.go

@@ -53,6 +53,7 @@ type Flags struct {
 	EnableDutiesV2                      bool // EnableDutiesV2 sets validator client to use the get Duties V2 endpoint
 	EnableWeb                           bool // EnableWeb enables the webui on the validator client
 	SSZOnly                             bool // SSZOnly forces the validator client to use SSZ for communication with the beacon node when REST mode is enabled (useful for debugging)
+	EnableStateDiff                     bool // EnableStateDiff enables the experimental state diff feature for the beacon node.
 	// Logging related toggles.
 	DisableGRPCConnectionLogs bool // Disables logging when a new grpc client has connected.
 	EnableFullSSZDataLogging  bool // Enables logging for full ssz data on rejected gossip messages
@@ -277,6 +278,10 @@ func ConfigureBeaconChain(ctx *cli.Context) error {
 		logEnabled(enableExperimentalAttestationPool)
 		cfg.EnableExperimentalAttestationPool = true
 	}
+	if ctx.IsSet(enableStateDiff.Name) {
+		logEnabled(enableStateDiff)
+		cfg.EnableStateDiff = true
+	}
 	if ctx.IsSet(forceHeadFlag.Name) {
 		logEnabled(forceHeadFlag)
 		cfg.ForceHead = ctx.String(forceHeadFlag.Name)

config/features/flags.go

@@ -176,6 +176,10 @@ var (
 		Name:  "enable-experimental-attestation-pool",
 		Usage: "Enables an experimental attestation pool design.",
 	}
+	enableStateDiff = &cli.BoolFlag{
+		Name:  "enable-state-diff",
+		Usage: "Enables the experimental state diff feature.",
+	}
 	// forceHeadFlag is a flag to force the head of the beacon chain to a specific block.
 	forceHeadFlag = &cli.StringFlag{
 		Name: "sync-from",
@@ -267,6 +271,7 @@ var BeaconChainFlags = combinedFlags([]cli.Flag{
 	DisableQUIC,
 	EnableDiscoveryReboot,
 	enableExperimentalAttestationPool,
+	enableStateDiff,
 	forceHeadFlag,
 	blacklistRoots,
 }, deprecatedBeaconFlags, deprecatedFlags, upcomingDeprecation)

config/params/BUILD.bazel

@@ -14,6 +14,7 @@ go_library(
         "mainnet_config.go",
         "minimal_config.go",
         "network_config.go",
+        "state_diff_config.go",
         "testnet_e2e_config.go",
         "testnet_holesky_config.go",
         "testnet_hoodi_config.go",

config/params/state_diff_config.go

@@ -0,0 +1,9 @@
+package params
+
+var (
+	stateHierarchyExponents = []uint64{21, 18, 16, 13, 11, 9, 5}
+)
+
+func StateHierarchyExponents() []uint64 {
+	return stateHierarchyExponents
+}

consensus-types/blocks/execution.go

@@ -40,6 +40,12 @@ func NewWrappedExecutionData(v proto.Message) (interfaces.ExecutionData, error)
 	case *enginev1.ExecutionBundleElectra:
 		// note: no payload changes in electra so using deneb
 		return WrappedExecutionPayloadDeneb(pbStruct.Payload)
+	case *enginev1.ExecutionPayloadHeader:
+		return WrappedExecutionPayloadHeader(pbStruct)
+	case *enginev1.ExecutionPayloadHeaderCapella:
+		return WrappedExecutionPayloadHeaderCapella(pbStruct)
+	case *enginev1.ExecutionPayloadHeaderDeneb:
+		return WrappedExecutionPayloadHeaderDeneb(pbStruct)
 	default:
 		return nil, ErrUnsupportedVersion
 	}

consensus-types/hdiff/BUILD.bazel

@@ -0,0 +1,53 @@
+load("@prysm//tools/go:def.bzl", "go_library", "go_test")
+
+go_library(
+    name = "go_default_library",
+    srcs = ["state_diff.go"],
+    importpath = "github.com/OffchainLabs/prysm/v6/consensus-types/hdiff",
+    visibility = ["//visibility:public"],
+    deps = [
+        "//beacon-chain/core/altair:go_default_library",
+        "//beacon-chain/core/capella:go_default_library",
+        "//beacon-chain/core/deneb:go_default_library",
+        "//beacon-chain/core/electra:go_default_library",
+        "//beacon-chain/core/execution:go_default_library",
+        "//beacon-chain/state:go_default_library",
+        "//config/fieldparams:go_default_library",
+        "//consensus-types/blocks:go_default_library",
+        "//consensus-types/helpers:go_default_library",
+        "//consensus-types/interfaces:go_default_library",
+        "//consensus-types/primitives:go_default_library",
+        "//proto/engine/v1:go_default_library",
+        "//proto/prysm/v1alpha1:go_default_library",
+        "//runtime/version:go_default_library",
+        "@com_github_golang_snappy//:go_default_library",
+        "@com_github_pkg_errors//:go_default_library",
+        "@com_github_prysmaticlabs_fastssz//:go_default_library",
+        "@com_github_prysmaticlabs_go_bitfield//:go_default_library",
+        "@com_github_sirupsen_logrus//:go_default_library",
+        "@org_golang_google_protobuf//proto:go_default_library",
+    ],
+)
+
+go_test(
+    name = "go_default_test",
+    srcs = [
+        "fuzz_test.go",
+        "property_test.go",
+        "security_test.go",
+        "state_diff_test.go",
+    ],
+    embed = [":go_default_library"],
+    deps = [
+        "//beacon-chain/core/transition:go_default_library",
+        "//beacon-chain/state:go_default_library",
+        "//beacon-chain/state/state-native:go_default_library",
+        "//consensus-types/blocks:go_default_library",
+        "//consensus-types/primitives:go_default_library",
+        "//proto/prysm/v1alpha1:go_default_library",
+        "//testing/require:go_default_library",
+        "//testing/util:go_default_library",
+        "@com_github_golang_snappy//:go_default_library",
+        "@com_github_pkg_errors//:go_default_library",
+    ],
+)

consensus-types/hdiff/fuzz_test.go

@@ -0,0 +1,491 @@
+package hdiff
+
+import (
+	"context"
+	"encoding/binary"
+	"strconv"
+	"strings"
+	"testing"
+
+	ethpb "github.com/OffchainLabs/prysm/v6/proto/prysm/v1alpha1"
+	"github.com/OffchainLabs/prysm/v6/testing/util"
+)
+
+// FuzzNewHdiff tests parsing variations of realistic diffs
+func FuzzNewHdiff(f *testing.F) {
+	// Add seed corpus with various valid diffs from realistic scenarios
+	sizes := []uint64{8, 16, 32}
+	for _, size := range sizes {
+		source, _ := util.DeterministicGenesisStateElectra(f, size)
+		
+		// Create various realistic target states
+		scenarios := []string{"slot_change", "balance_change", "validator_change", "multiple_changes"}
+		for _, scenario := range scenarios {
+			target := source.Copy()
+			
+			switch scenario {
+			case "slot_change":
+				_ = target.SetSlot(source.Slot() + 1)
+			case "balance_change":
+				balances := target.Balances()
+				if len(balances) > 0 {
+					balances[0] += 1000000000
+					_ = target.SetBalances(balances)
+				}
+			case "validator_change":
+				validators := target.Validators()
+				if len(validators) > 0 {
+					validators[0].EffectiveBalance += 1000000000
+					_ = target.SetValidators(validators)
+				}
+			case "multiple_changes":
+				_ = target.SetSlot(source.Slot() + 5)
+				balances := target.Balances()
+				validators := target.Validators()
+				if len(balances) > 0 && len(validators) > 0 {
+					balances[0] += 2000000000
+					validators[0].EffectiveBalance += 1000000000
+					_ = target.SetBalances(balances)
+					_ = target.SetValidators(validators)
+				}
+			}
+			
+			validDiff, err := Diff(source, target)
+			if err == nil {
+				f.Add(validDiff.StateDiff, validDiff.ValidatorDiffs, validDiff.BalancesDiff)
+			}
+		}
+	}
+	
+	f.Fuzz(func(t *testing.T, stateDiff, validatorDiffs, balancesDiff []byte) {
+		// Limit input sizes to reasonable bounds
+		if len(stateDiff) > 5000 || len(validatorDiffs) > 5000 || len(balancesDiff) > 5000 {
+			return
+		}
+		
+		input := HdiffBytes{
+			StateDiff:      stateDiff,
+			ValidatorDiffs: validatorDiffs,
+			BalancesDiff:   balancesDiff,
+		}
+		
+		// Test parsing - should not panic even with corrupted but bounded data
+		_, err := newHdiff(input)
+		_ = err // Expected to fail with corrupted data
+	})
+}
+
+// FuzzNewStateDiff tests the newStateDiff function with random compressed input
+func FuzzNewStateDiff(f *testing.F) {
+	// Add seed corpus
+	source, _ := util.DeterministicGenesisStateElectra(f, 16)
+	target := source.Copy()
+	_ = target.SetSlot(source.Slot() + 5)
+	
+	diff, err := diffToState(source, target)
+	if err == nil {
+		serialized := diff.serialize()
+		f.Add(serialized)
+	}
+	
+	// Add edge cases
+	f.Add([]byte{})
+	f.Add([]byte{0x01})
+	f.Add([]byte{0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07})
+	
+	f.Fuzz(func(t *testing.T, data []byte) {
+		defer func() {
+			if r := recover(); r != nil {
+				t.Errorf("newStateDiff panicked: %v", r)
+			}
+		}()
+		
+		// Should never panic, only return error
+		_, err := newStateDiff(data)
+		_ = err
+	})
+}
+
+// FuzzNewValidatorDiffs tests validator diff deserialization
+func FuzzNewValidatorDiffs(f *testing.F) {
+	// Add seed corpus
+	source, _ := util.DeterministicGenesisStateElectra(f, 8)
+	target := source.Copy()
+	vals := target.Validators()
+	if len(vals) > 0 {
+		modifiedVal := &ethpb.Validator{
+			PublicKey:                  vals[0].PublicKey,
+			WithdrawalCredentials:      vals[0].WithdrawalCredentials,
+			EffectiveBalance:           vals[0].EffectiveBalance + 1000,
+			Slashed:                    !vals[0].Slashed,
+			ActivationEligibilityEpoch: vals[0].ActivationEligibilityEpoch,
+			ActivationEpoch:            vals[0].ActivationEpoch,
+			ExitEpoch:                  vals[0].ExitEpoch,
+			WithdrawableEpoch:          vals[0].WithdrawableEpoch,
+		}
+		vals[0] = modifiedVal
+		_ = target.SetValidators(vals)
+		
+		// Create a simple diff for fuzzing - we'll just use raw bytes
+		_, err := diffToVals(source, target)
+		if err == nil {
+			// Add some realistic validator diff bytes for the corpus
+			f.Add([]byte{1, 0, 0, 0, 0, 0, 0, 0}) // Simple validator diff
+		}
+	}
+	
+	// Add edge cases
+	f.Add([]byte{})
+	f.Add([]byte{0x01, 0x02, 0x03, 0x04})
+	
+	f.Fuzz(func(t *testing.T, data []byte) {
+		defer func() {
+			if r := recover(); r != nil {
+				t.Errorf("newValidatorDiffs panicked: %v", r)
+			}
+		}()
+		
+		_, err := newValidatorDiffs(data)
+		_ = err
+	})
+}
+
+// FuzzNewBalancesDiff tests balance diff deserialization
+func FuzzNewBalancesDiff(f *testing.F) {
+	// Add seed corpus
+	source, _ := util.DeterministicGenesisStateElectra(f, 8)
+	target := source.Copy()
+	balances := target.Balances()
+	if len(balances) > 0 {
+		balances[0] += 1000
+		_ = target.SetBalances(balances)
+		
+		// Create a simple diff for fuzzing - we'll just use raw bytes
+		_, err := diffToBalances(source, target)
+		if err == nil {
+			// Add some realistic balance diff bytes for the corpus
+			f.Add([]byte{1, 0, 0, 0, 0, 0, 0, 0}) // Simple balance diff
+		}
+	}
+	
+	// Add edge cases
+	f.Add([]byte{})
+	f.Add([]byte{0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08})
+	
+	f.Fuzz(func(t *testing.T, data []byte) {
+		defer func() {
+			if r := recover(); r != nil {
+				t.Errorf("newBalancesDiff panicked: %v", r)
+			}
+		}()
+		
+		_, err := newBalancesDiff(data)
+		_ = err
+	})
+}
+
+// FuzzApplyDiff tests applying variations of valid diffs
+func FuzzApplyDiff(f *testing.F) {
+	// Test with realistic state variations, not random data
+	ctx := context.Background()
+	
+	// Add seed corpus with various valid scenarios
+	sizes := []uint64{8, 16, 32, 64}
+	for _, size := range sizes {
+		source, _ := util.DeterministicGenesisStateElectra(f, size)
+		target := source.Copy()
+		
+		// Different types of realistic changes
+		scenarios := []func(){
+			func() { _ = target.SetSlot(source.Slot() + 1) }, // Slot change
+			func() { // Balance change
+				balances := target.Balances()
+				if len(balances) > 0 {
+					balances[0] += 1000000000 // 1 ETH
+					_ = target.SetBalances(balances)
+				}
+			},
+			func() { // Validator change
+				validators := target.Validators()
+				if len(validators) > 0 {
+					validators[0].EffectiveBalance += 1000000000
+					_ = target.SetValidators(validators)
+				}
+			},
+		}
+		
+		for _, scenario := range scenarios {
+			testTarget := source.Copy()
+			scenario()
+			
+			validDiff, err := Diff(source, testTarget)
+			if err == nil {
+				f.Add(validDiff.StateDiff, validDiff.ValidatorDiffs, validDiff.BalancesDiff)
+			}
+		}
+	}
+	
+	f.Fuzz(func(t *testing.T, stateDiff, validatorDiffs, balancesDiff []byte) {
+		// Only test with reasonable sized inputs
+		if len(stateDiff) > 10000 || len(validatorDiffs) > 10000 || len(balancesDiff) > 10000 {
+			return
+		}
+		
+		// Create fresh source state for each test
+		source, _ := util.DeterministicGenesisStateElectra(t, 8)
+		
+		diff := HdiffBytes{
+			StateDiff:      stateDiff,
+			ValidatorDiffs: validatorDiffs,
+			BalancesDiff:   balancesDiff,
+		}
+		
+		// Apply diff - errors are expected for fuzzed data
+		_, err := ApplyDiff(ctx, source, diff)
+		_ = err // Expected to fail with invalid data
+	})
+}
+
+// FuzzReadPendingAttestation tests the pending attestation deserialization
+func FuzzReadPendingAttestation(f *testing.F) {
+	// Add edge cases - this function is particularly vulnerable
+	f.Add([]byte{})
+	f.Add([]byte{0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08}) // 8 bytes
+	f.Add(make([]byte, 200)) // Larger than expected
+	
+	// Add a case with large reported length
+	largeLength := make([]byte, 8)
+	binary.LittleEndian.PutUint64(largeLength, 0xFFFFFFFF) // Large bits length
+	f.Add(largeLength)
+	
+	f.Fuzz(func(t *testing.T, data []byte) {
+		defer func() {
+			if r := recover(); r != nil {
+				t.Errorf("readPendingAttestation panicked: %v", r)
+			}
+		}()
+		
+		// Make a copy since the function modifies the slice
+		dataCopy := make([]byte, len(data))
+		copy(dataCopy, data)
+		
+		_, err := readPendingAttestation(&dataCopy)
+		_ = err
+	})
+}
+
+// FuzzKmpIndex tests the KMP algorithm implementation
+func FuzzKmpIndex(f *testing.F) {
+	// Test with integer pointers to match the actual usage
+	f.Add(0, "1,2,3", "1,2,3,4,5")
+	f.Add(3, "1,2,3", "1,2,3,1,2,3")
+	f.Add(0, "", "1,2,3")
+	
+	f.Fuzz(func(t *testing.T, lens int, patternStr string, textStr string) {
+		defer func() {
+			if r := recover(); r != nil {
+				t.Errorf("kmpIndex panicked: %v", r)
+			}
+		}()
+		
+		// Parse comma-separated strings into int slices
+		var pattern, text []int
+		if patternStr != "" {
+			for _, s := range strings.Split(patternStr, ",") {
+				if val, err := strconv.Atoi(strings.TrimSpace(s)); err == nil {
+					pattern = append(pattern, val)
+				}
+			}
+		}
+		if textStr != "" {
+			for _, s := range strings.Split(textStr, ",") {
+				if val, err := strconv.Atoi(strings.TrimSpace(s)); err == nil {
+					text = append(text, val)
+				}
+			}
+		}
+		
+		// Convert to pointer slices as used in actual code
+		patternPtrs := make([]*int, len(pattern))
+		for i := range pattern {
+			val := pattern[i]
+			patternPtrs[i] = &val
+		}
+		
+		textPtrs := make([]*int, len(text))
+		for i := range text {
+			val := text[i]
+			textPtrs[i] = &val
+		}
+		
+		integerEquals := func(a, b *int) bool {
+			if a == nil && b == nil {
+				return true
+			}
+			if a == nil || b == nil {
+				return false
+			}
+			return *a == *b
+		}
+		
+		// Clamp lens to reasonable range to avoid infinite loops
+		if lens < 0 {
+			lens = 0
+		}
+		if lens > len(textPtrs) {
+			lens = len(textPtrs)
+		}
+		
+		result := kmpIndex(lens, textPtrs, integerEquals)
+		
+		// Basic sanity check
+		if result < 0 || result > lens {
+			t.Errorf("kmpIndex returned invalid result: %d for lens=%d", result, lens)
+		}
+	})
+}
+
+// FuzzComputeLPS tests the LPS computation for KMP
+func FuzzComputeLPS(f *testing.F) {
+	// Add seed cases
+	f.Add("1,2,1")
+	f.Add("1,1,1")
+	f.Add("1,2,3,4")
+	f.Add("")
+	
+	f.Fuzz(func(t *testing.T, patternStr string) {
+		defer func() {
+			if r := recover(); r != nil {
+				t.Errorf("computeLPS panicked: %v", r)
+			}
+		}()
+		
+		// Parse comma-separated string into int slice
+		var pattern []int
+		if patternStr != "" {
+			for _, s := range strings.Split(patternStr, ",") {
+				if val, err := strconv.Atoi(strings.TrimSpace(s)); err == nil {
+					pattern = append(pattern, val)
+				}
+			}
+		}
+		
+		// Convert to pointer slice
+		patternPtrs := make([]*int, len(pattern))
+		for i := range pattern {
+			val := pattern[i]
+			patternPtrs[i] = &val
+		}
+		
+		integerEquals := func(a, b *int) bool {
+			if a == nil && b == nil {
+				return true
+			}
+			if a == nil || b == nil {
+				return false
+			}
+			return *a == *b
+		}
+		
+		result := computeLPS(patternPtrs, integerEquals)
+		
+		// Verify result length matches input
+		if len(result) != len(pattern) {
+			t.Errorf("computeLPS returned wrong length: got %d, expected %d", len(result), len(pattern))
+		}
+		
+		// Verify all LPS values are non-negative and within bounds
+		for i, lps := range result {
+			if lps < 0 || lps > i {
+				t.Errorf("Invalid LPS value at index %d: %d", i, lps)
+			}
+		}
+	})
+}
+
+// FuzzDiffToBalances tests balance diff computation
+func FuzzDiffToBalances(f *testing.F) {
+	f.Fuzz(func(t *testing.T, sourceData, targetData []byte) {
+		defer func() {
+			if r := recover(); r != nil {
+				t.Errorf("diffToBalances panicked: %v", r)
+			}
+		}()
+		
+		// Convert byte data to balance arrays
+		var sourceBalances, targetBalances []uint64
+		
+		// Parse source balances (8 bytes per uint64)
+		for i := 0; i+7 < len(sourceData) && len(sourceBalances) < 100; i += 8 {
+			balance := binary.LittleEndian.Uint64(sourceData[i : i+8])
+			sourceBalances = append(sourceBalances, balance)
+		}
+		
+		// Parse target balances
+		for i := 0; i+7 < len(targetData) && len(targetBalances) < 100; i += 8 {
+			balance := binary.LittleEndian.Uint64(targetData[i : i+8])
+			targetBalances = append(targetBalances, balance)
+		}
+		
+		// Create states with the provided balances
+		source, _ := util.DeterministicGenesisStateElectra(t, 1)
+		target, _ := util.DeterministicGenesisStateElectra(t, 1)
+		
+		if len(sourceBalances) > 0 {
+			_ = source.SetBalances(sourceBalances)
+		}
+		if len(targetBalances) > 0 {
+			_ = target.SetBalances(targetBalances)
+		}
+		
+		result, err := diffToBalances(source, target)
+		
+		// If no error, verify result consistency
+		if err == nil && len(result) > 0 {
+			// Result length should match target length
+			if len(result) != len(target.Balances()) {
+				t.Errorf("diffToBalances result length mismatch: got %d, expected %d", 
+					len(result), len(target.Balances()))
+			}
+		}
+	})
+}
+
+// FuzzValidatorsEqual tests validator comparison
+func FuzzValidatorsEqual(f *testing.F) {
+	f.Fuzz(func(t *testing.T, data []byte) {
+		defer func() {
+			if r := recover(); r != nil {
+				t.Errorf("validatorsEqual panicked: %v", r)
+			}
+		}()
+		
+		// Create two validators and fuzz their fields
+		if len(data) < 16 {
+			return
+		}
+		
+		source, _ := util.DeterministicGenesisStateElectra(t, 2)
+		validators := source.Validators()
+		if len(validators) < 2 {
+			return
+		}
+		
+		val1 := validators[0]
+		val2 := validators[1]
+		
+		// Modify validator fields based on fuzz data
+		if len(data) > 0 && data[0]%2 == 0 {
+			val2.EffectiveBalance = val1.EffectiveBalance + uint64(data[0])
+		}
+		if len(data) > 1 && data[1]%2 == 0 {
+			val2.Slashed = !val1.Slashed
+		}
+		
+		// Create ReadOnlyValidator wrappers if needed
+		// Since validatorsEqual expects ReadOnlyValidator interface,
+		// we'll skip this test for now as it requires state wrapper implementation
+		_ = val1
+		_ = val2
+	})
+}

consensus-types/hdiff/property_test.go

@@ -0,0 +1,391 @@
+package hdiff
+
+import (
+	"context"
+	"encoding/binary"
+	"math"
+	"testing"
+	"time"
+
+	"github.com/OffchainLabs/prysm/v6/consensus-types/primitives"
+	"github.com/OffchainLabs/prysm/v6/testing/require"
+	"github.com/OffchainLabs/prysm/v6/testing/util"
+)
+
+// PropertyTestRoundTrip verifies that diff->apply is idempotent with realistic data
+func FuzzPropertyRoundTrip(f *testing.F) {
+	f.Fuzz(func(t *testing.T, slotDelta uint64, balanceData []byte, validatorData []byte) {
+		// Limit to realistic ranges
+		if slotDelta > 32 { // Max one epoch
+			slotDelta = slotDelta % 32
+		}
+		
+		// Convert byte data to realistic deltas and changes
+		var balanceDeltas []int64
+		var validatorChanges []bool
+		
+		// Parse balance deltas - limit to realistic amounts (8 bytes per int64)
+		for i := 0; i+7 < len(balanceData) && len(balanceDeltas) < 20; i += 8 {
+			delta := int64(binary.LittleEndian.Uint64(balanceData[i : i+8]))
+			// Keep deltas realistic (max 10 ETH change)
+			if delta > 10000000000 {
+				delta = delta % 10000000000
+			}
+			if delta < -10000000000 {
+				delta = -((-delta) % 10000000000)
+			}
+			balanceDeltas = append(balanceDeltas, delta)
+		}
+		
+		// Parse validator changes (1 byte per bool) - limit to small number
+		for i := 0; i < len(validatorData) && len(validatorChanges) < 10; i++ {
+			validatorChanges = append(validatorChanges, validatorData[i]%2 == 0)
+		}
+		
+		ctx := context.Background()
+		
+		// Create source state with reasonable size
+		validatorCount := uint64(len(validatorChanges) + 8) // Minimum 8 validators
+		if validatorCount > 64 {
+			validatorCount = 64 // Cap at 64 for performance
+		}
+		source, _ := util.DeterministicGenesisStateElectra(t, validatorCount)
+		
+		// Create target state with modifications
+		target := source.Copy()
+		
+		// Apply slot change
+		_ = target.SetSlot(source.Slot() + primitives.Slot(slotDelta))
+		
+		// Apply realistic balance changes
+		if len(balanceDeltas) > 0 {
+			balances := target.Balances()
+			for i, delta := range balanceDeltas {
+				if i >= len(balances) {
+					break
+				}
+				// Apply realistic balance changes with safe bounds
+				if delta < 0 {
+					if uint64(-delta) > balances[i] {
+						balances[i] = 0 // Can't go below 0
+					} else {
+						balances[i] -= uint64(-delta)
+					}
+				} else {
+					// Cap at reasonable maximum (1000 ETH)
+					maxBalance := uint64(1000000000000) // 1000 ETH in Gwei
+					if balances[i]+uint64(delta) > maxBalance {
+						balances[i] = maxBalance
+					} else {
+						balances[i] += uint64(delta)
+					}
+				}
+			}
+			_ = target.SetBalances(balances)
+		}
+		
+		// Apply realistic validator changes
+		if len(validatorChanges) > 0 {
+			validators := target.Validators()
+			for i, shouldChange := range validatorChanges {
+				if i >= len(validators) {
+					break
+				}
+				if shouldChange {
+					// Make realistic changes - small effective balance adjustments
+					validators[i].EffectiveBalance += 1000000000 // 1 ETH
+				}
+			}
+			_ = target.SetValidators(validators)
+		}
+		
+		// Create diff
+		diff, err := Diff(source, target)
+		if err != nil {
+			// If diff creation fails, that's acceptable for malformed inputs
+			return
+		}
+		
+		// Apply diff
+		result, err := ApplyDiff(ctx, source, diff)
+		if err != nil {
+			// If diff application fails, that's acceptable
+			return
+		}
+		
+		// Verify round-trip property: source + diff = target
+		require.Equal(t, target.Slot(), result.Slot())
+		
+		// Verify balance consistency
+		targetBalances := target.Balances()
+		resultBalances := result.Balances()
+		require.Equal(t, len(targetBalances), len(resultBalances))
+		for i := range targetBalances {
+			require.Equal(t, targetBalances[i], resultBalances[i], "Balance mismatch at index %d", i)
+		}
+		
+		// Verify validator consistency
+		targetVals := target.Validators()
+		resultVals := result.Validators()
+		require.Equal(t, len(targetVals), len(resultVals))
+		for i := range targetVals {
+			require.Equal(t, targetVals[i].Slashed, resultVals[i].Slashed, "Validator slashing mismatch at index %d", i)
+			require.Equal(t, targetVals[i].EffectiveBalance, resultVals[i].EffectiveBalance, "Validator balance mismatch at index %d", i)
+		}
+	})
+}
+
+// PropertyTestReasonablePerformance verifies operations complete quickly with realistic data
+func FuzzPropertyResourceBounds(f *testing.F) {
+	f.Fuzz(func(t *testing.T, validatorCount uint8, slotDelta uint8, changeCount uint8) {
+		// Use realistic parameters
+		validators := uint64(validatorCount%64 + 8) // 8-71 validators
+		slots := uint64(slotDelta % 32)              // 0-31 slots
+		changes := int(changeCount % 10)            // 0-9 changes
+		
+		// Create realistic states
+		source, _ := util.DeterministicGenesisStateElectra(t, validators)
+		target := source.Copy()
+		
+		// Apply realistic changes
+		_ = target.SetSlot(source.Slot() + primitives.Slot(slots))
+		
+		if changes > 0 {
+			validatorList := target.Validators()
+			for i := 0; i < changes && i < len(validatorList); i++ {
+				validatorList[i].EffectiveBalance += 1000000000 // 1 ETH
+			}
+			_ = target.SetValidators(validatorList)
+		}
+		
+		// Operations should complete quickly
+		start := time.Now()
+		diff, err := Diff(source, target)
+		duration := time.Since(start)
+		
+		if err == nil {
+			// Should be fast
+			require.Equal(t, true, duration < time.Second, "Diff creation too slow: %v", duration)
+			
+			// Apply should also be fast
+			start = time.Now()
+			_, err = ApplyDiff(context.Background(), source, diff)
+			duration = time.Since(start)
+			
+			if err == nil {
+				require.Equal(t, true, duration < time.Second, "Diff application too slow: %v", duration)
+			}
+		}
+	})
+}
+
+// PropertyTestDiffSize verifies that diffs are smaller than full states for typical cases
+func FuzzPropertyDiffEfficiency(f *testing.F) {
+	f.Fuzz(func(t *testing.T, slotDelta uint64, numChanges uint8) {
+		if slotDelta > 100 {
+			slotDelta = slotDelta % 100
+		}
+		if numChanges > 10 {
+			numChanges = numChanges % 10
+		}
+		
+		// Create states with small differences
+		source, _ := util.DeterministicGenesisStateElectra(t, 64)
+		target := source.Copy()
+		
+		_ = target.SetSlot(source.Slot() + primitives.Slot(slotDelta))
+		
+		// Make a few small changes
+		if numChanges > 0 {
+			validators := target.Validators()
+			for i := uint8(0); i < numChanges && int(i) < len(validators); i++ {
+				validators[i].EffectiveBalance += 1000
+			}
+			_ = target.SetValidators(validators)
+		}
+		
+		// Create diff
+		diff, err := Diff(source, target)
+		if err != nil {
+			return
+		}
+		
+		// For small changes, diff should be much smaller than full state
+		sourceSSZ, err := source.MarshalSSZ()
+		if err != nil {
+			return
+		}
+		
+		diffSize := len(diff.StateDiff) + len(diff.ValidatorDiffs) + len(diff.BalancesDiff)
+		
+		// Diff should be smaller than full state for small changes
+		if numChanges <= 5 && slotDelta <= 10 {
+			require.Equal(t, true, diffSize < len(sourceSSZ)/2, 
+				"Diff size %d should be less than half of state size %d", diffSize, len(sourceSSZ))
+		}
+	})
+}
+
+// PropertyTestBalanceConservation verifies that balance operations don't create/destroy value unexpectedly
+func FuzzPropertyBalanceConservation(f *testing.F) {
+	f.Fuzz(func(t *testing.T, balanceData []byte) {
+		// Convert byte data to balance changes
+		var balanceChanges []int64
+		for i := 0; i+7 < len(balanceData) && len(balanceChanges) < 50; i += 8 {
+			change := int64(binary.LittleEndian.Uint64(balanceData[i : i+8]))
+			balanceChanges = append(balanceChanges, change)
+		}
+		
+		source, _ := util.DeterministicGenesisStateElectra(t, uint64(len(balanceChanges)+10))
+		originalBalances := source.Balances()
+		
+		// Calculate total before
+		var totalBefore uint64
+		for _, balance := range originalBalances {
+			totalBefore += balance
+		}
+		
+		// Apply balance changes via diff system
+		target := source.Copy()
+		targetBalances := target.Balances()
+		
+		var totalDelta int64
+		for i, delta := range balanceChanges {
+			if i >= len(targetBalances) {
+				break
+			}
+			
+			// Prevent underflow
+			if delta < 0 && uint64(-delta) > targetBalances[i] {
+				totalDelta += int64(targetBalances[i]) // Lost amount
+				targetBalances[i] = 0
+			} else if delta < 0 {
+				targetBalances[i] -= uint64(-delta)
+				totalDelta += delta
+			} else {
+				// Prevent overflow
+				if uint64(delta) > math.MaxUint64-targetBalances[i] {
+					gained := math.MaxUint64 - targetBalances[i]
+					totalDelta += int64(gained)
+					targetBalances[i] = math.MaxUint64
+				} else {
+					targetBalances[i] += uint64(delta)
+					totalDelta += delta
+				}
+			}
+		}
+		_ = target.SetBalances(targetBalances)
+		
+		// Apply through diff system
+		diff, err := Diff(source, target)
+		if err != nil {
+			return
+		}
+		
+		result, err := ApplyDiff(context.Background(), source, diff)
+		if err != nil {
+			return
+		}
+		
+		// Calculate total after
+		resultBalances := result.Balances()
+		var totalAfter uint64
+		for _, balance := range resultBalances {
+			totalAfter += balance
+		}
+		
+		// Verify conservation (accounting for intended changes)
+		expectedTotal := totalBefore
+		if totalDelta >= 0 {
+			expectedTotal += uint64(totalDelta)
+		} else {
+			if uint64(-totalDelta) <= expectedTotal {
+				expectedTotal -= uint64(-totalDelta)
+			} else {
+				expectedTotal = 0
+			}
+		}
+		
+		require.Equal(t, expectedTotal, totalAfter, 
+			"Balance conservation violated: before=%d, delta=%d, expected=%d, actual=%d", 
+			totalBefore, totalDelta, expectedTotal, totalAfter)
+	})
+}
+
+// PropertyTestMonotonicSlot verifies slot only increases
+func FuzzPropertyMonotonicSlot(f *testing.F) {
+	f.Fuzz(func(t *testing.T, slotDelta uint64) {
+		source, _ := util.DeterministicGenesisStateElectra(t, 16)
+		target := source.Copy()
+		
+		targetSlot := source.Slot() + primitives.Slot(slotDelta)
+		_ = target.SetSlot(targetSlot)
+		
+		diff, err := Diff(source, target)
+		if err != nil {
+			return
+		}
+		
+		result, err := ApplyDiff(context.Background(), source, diff)
+		if err != nil {
+			return
+		}
+		
+		// Slot should never decrease
+		require.Equal(t, true, result.Slot() >= source.Slot(), 
+			"Slot decreased from %d to %d", source.Slot(), result.Slot())
+		
+		// Slot should match target
+		require.Equal(t, targetSlot, result.Slot())
+	})
+}
+
+// PropertyTestValidatorIndexIntegrity verifies validator indices remain consistent
+func FuzzPropertyValidatorIndices(f *testing.F) {
+	f.Fuzz(func(t *testing.T, changeData []byte) {
+		// Convert byte data to boolean changes
+		var changes []bool
+		for i := 0; i < len(changeData) && len(changes) < 20; i++ {
+			changes = append(changes, changeData[i]%2 == 0)
+		}
+		
+		source, _ := util.DeterministicGenesisStateElectra(t, uint64(len(changes)+5))
+		target := source.Copy()
+		
+		// Apply changes
+		validators := target.Validators()
+		for i, shouldChange := range changes {
+			if i >= len(validators) {
+				break
+			}
+			if shouldChange {
+				validators[i].EffectiveBalance += 1000
+			}
+		}
+		_ = target.SetValidators(validators)
+		
+		diff, err := Diff(source, target)
+		if err != nil {
+			return
+		}
+		
+		result, err := ApplyDiff(context.Background(), source, diff)
+		if err != nil {
+			return
+		}
+		
+		// Validator count should not decrease
+		require.Equal(t, true, len(result.Validators()) >= len(source.Validators()),
+			"Validator count decreased from %d to %d", len(source.Validators()), len(result.Validators()))
+		
+		// Public keys should be preserved for existing validators
+		sourceVals := source.Validators()
+		resultVals := result.Validators()
+		for i := range sourceVals {
+			if i < len(resultVals) {
+				require.Equal(t, sourceVals[i].PublicKey, resultVals[i].PublicKey,
+					"Public key changed at validator index %d", i)
+			}
+		}
+	})
+}

consensus-types/hdiff/security_test.go

@@ -0,0 +1,393 @@
+package hdiff
+
+import (
+	"context"
+	"fmt"
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/OffchainLabs/prysm/v6/testing/require"
+	"github.com/OffchainLabs/prysm/v6/testing/util"
+)
+
+// TestIntegerOverflowProtection tests protection against balance overflow attacks
+func TestIntegerOverflowProtection(t *testing.T) {
+	source, _ := util.DeterministicGenesisStateElectra(t, 8)
+	
+	// Test balance overflow in diffToBalances - use realistic values
+	t.Run("balance_diff_overflow", func(t *testing.T) {
+		target := source.Copy()
+		balances := target.Balances()
+		
+		// Set high but realistic balance values (32 ETH in Gwei = 32e9)
+		balances[0] = 32000000000 // 32 ETH
+		balances[1] = 64000000000 // 64 ETH
+		_ = target.SetBalances(balances)
+		
+		// This should work fine with realistic values
+		diffs, err := diffToBalances(source, target)
+		require.NoError(t, err)
+		
+		// Verify the diffs are reasonable
+		require.Equal(t, true, len(diffs) > 0, "Should have balance diffs")
+	})
+	
+	// Test reasonable balance changes
+	t.Run("realistic_balance_changes", func(t *testing.T) {
+		// Create realistic balance changes (slashing, rewards)
+		balancesDiff := []int64{1000000000, -500000000, 2000000000} // 1 ETH gain, 0.5 ETH loss, 2 ETH gain
+		
+		// Apply to state with normal balances
+		testSource := source.Copy()
+		normalBalances := []uint64{32000000000, 32000000000, 32000000000} // 32 ETH each
+		_ = testSource.SetBalances(normalBalances)
+		
+		// This should work fine
+		result, err := applyBalancesDiff(testSource, balancesDiff)
+		require.NoError(t, err)
+		
+		resultBalances := result.Balances()
+		require.Equal(t, uint64(33000000000), resultBalances[0]) // 33 ETH
+		require.Equal(t, uint64(31500000000), resultBalances[1]) // 31.5 ETH
+		require.Equal(t, uint64(34000000000), resultBalances[2]) // 34 ETH
+	})
+}
+
+// TestReasonablePerformance tests that operations complete in reasonable time
+func TestReasonablePerformance(t *testing.T) {
+	t.Run("large_state_performance", func(t *testing.T) {
+		// Test with a large but realistic validator set
+		source, _ := util.DeterministicGenesisStateElectra(t, 1000) // 1000 validators
+		target := source.Copy()
+		
+		// Make realistic changes
+		_ = target.SetSlot(source.Slot() + 32) // One epoch
+		validators := target.Validators()
+		for i := 0; i < 100; i++ { // 10% of validators changed
+			validators[i].EffectiveBalance += 1000000000 // 1 ETH change
+		}
+		_ = target.SetValidators(validators)
+		
+		// Should complete quickly
+		start := time.Now()
+		diff, err := Diff(source, target)
+		duration := time.Since(start)
+		
+		require.NoError(t, err)
+		require.Equal(t, true, duration < time.Second, "Diff creation took too long: %v", duration)
+		require.Equal(t, true, len(diff.StateDiff) > 0, "Should have state diff")
+	})
+	
+	t.Run("realistic_diff_application", func(t *testing.T) {
+		// Test applying diffs to large states
+		source, _ := util.DeterministicGenesisStateElectra(t, 500)
+		target := source.Copy()
+		_ = target.SetSlot(source.Slot() + 1)
+		
+		// Create and apply diff
+		diff, err := Diff(source, target)
+		require.NoError(t, err)
+		
+		start := time.Now()
+		result, err := ApplyDiff(context.Background(), source, diff)
+		duration := time.Since(start)
+		
+		require.NoError(t, err)
+		require.Equal(t, target.Slot(), result.Slot())
+		require.Equal(t, true, duration < time.Second, "Diff application took too long: %v", duration)
+	})
+}
+
+// TestStateTransitionValidation tests realistic state transition scenarios
+func TestStateTransitionValidation(t *testing.T) {
+	t.Run("validator_slashing_scenario", func(t *testing.T) {
+		source, _ := util.DeterministicGenesisStateElectra(t, 10)
+		target := source.Copy()
+		
+		// Simulate validator slashing (realistic scenario)
+		validators := target.Validators()
+		validators[0].Slashed = true
+		validators[0].EffectiveBalance = 0 // Slashed validator loses balance
+		_ = target.SetValidators(validators)
+		
+		// This should work fine
+		diff, err := Diff(source, target)
+		require.NoError(t, err)
+		
+		result, err := ApplyDiff(context.Background(), source, diff)
+		require.NoError(t, err)
+		require.Equal(t, true, result.Validators()[0].Slashed)
+		require.Equal(t, uint64(0), result.Validators()[0].EffectiveBalance)
+	})
+	
+	t.Run("epoch_transition_scenario", func(t *testing.T) {
+		source, _ := util.DeterministicGenesisStateElectra(t, 64)
+		target := source.Copy()
+		
+		// Simulate epoch transition with multiple changes
+		_ = target.SetSlot(source.Slot() + 32) // One epoch
+		
+		// Some validators get rewards, others get penalties
+		balances := target.Balances()
+		for i := 0; i < len(balances); i++ {
+			if i%2 == 0 {
+				balances[i] += 100000000 // 0.1 ETH reward
+			} else {
+				if balances[i] > 50000000 {
+					balances[i] -= 50000000 // 0.05 ETH penalty
+				}
+			}
+		}
+		_ = target.SetBalances(balances)
+		
+		// This should work smoothly
+		diff, err := Diff(source, target)
+		require.NoError(t, err)
+		
+		result, err := ApplyDiff(context.Background(), source, diff)
+		require.NoError(t, err)
+		require.Equal(t, target.Slot(), result.Slot())
+	})
+	
+	t.Run("consistent_state_root", func(t *testing.T) {
+		// Test that diffs preserve state consistency
+		source, _ := util.DeterministicGenesisStateElectra(t, 32)
+		target := source.Copy()
+		
+		// Make minimal changes
+		_ = target.SetSlot(source.Slot() + 1)
+		
+		// Diff and apply should be consistent
+		diff, err := Diff(source, target)
+		require.NoError(t, err)
+		
+		result, err := ApplyDiff(context.Background(), source, diff)
+		require.NoError(t, err)
+		
+		// Result should match target
+		require.Equal(t, target.Slot(), result.Slot())
+		require.Equal(t, len(target.Validators()), len(result.Validators()))
+		require.Equal(t, len(target.Balances()), len(result.Balances()))
+	})
+}
+
+// TestSerializationRoundTrip tests serialization consistency
+func TestSerializationRoundTrip(t *testing.T) {
+	t.Run("diff_serialization_consistency", func(t *testing.T) {
+		// Test that serialization and deserialization are consistent
+		source, _ := util.DeterministicGenesisStateElectra(t, 16)
+		target := source.Copy()
+		
+		// Make changes
+		_ = target.SetSlot(source.Slot() + 5)
+		validators := target.Validators()
+		validators[0].EffectiveBalance += 1000000000
+		_ = target.SetValidators(validators)
+		
+		// Create diff
+		diff1, err := Diff(source, target)
+		require.NoError(t, err)
+		
+		// Deserialize and re-serialize
+		hdiff, err := newHdiff(diff1)
+		require.NoError(t, err)
+		
+		diff2 := hdiff.serialize()
+		
+		// Apply both diffs - should get same result
+		result1, err := ApplyDiff(context.Background(), source, diff1)
+		require.NoError(t, err)
+		
+		result2, err := ApplyDiff(context.Background(), source, diff2)
+		require.NoError(t, err)
+		
+		require.Equal(t, result1.Slot(), result2.Slot())
+		require.Equal(t, result1.Validators()[0].EffectiveBalance, result2.Validators()[0].EffectiveBalance)
+	})
+	
+	t.Run("empty_diff_handling", func(t *testing.T) {
+		// Test that empty diffs are handled correctly
+		source, _ := util.DeterministicGenesisStateElectra(t, 8)
+		target := source.Copy() // No changes
+		
+		// Should create minimal diff
+		diff, err := Diff(source, target)
+		require.NoError(t, err)
+		
+		// Apply should work and return equivalent state
+		result, err := ApplyDiff(context.Background(), source, diff)
+		require.NoError(t, err)
+		
+		require.Equal(t, source.Slot(), result.Slot())
+		require.Equal(t, len(source.Validators()), len(result.Validators()))
+	})
+	
+	t.Run("compression_efficiency", func(t *testing.T) {
+		// Test that compression is working effectively
+		source, _ := util.DeterministicGenesisStateElectra(t, 100)
+		target := source.Copy()
+		
+		// Make small changes
+		_ = target.SetSlot(source.Slot() + 1)
+		validators := target.Validators()
+		validators[0].EffectiveBalance += 1000000000
+		_ = target.SetValidators(validators)
+		
+		// Create diff
+		diff, err := Diff(source, target)
+		require.NoError(t, err)
+		
+		// Get full state size
+		fullStateSSZ, err := target.MarshalSSZ()
+		require.NoError(t, err)
+		
+		// Diff should be much smaller than full state
+		diffSize := len(diff.StateDiff) + len(diff.ValidatorDiffs) + len(diff.BalancesDiff)
+		require.Equal(t, true, diffSize < len(fullStateSSZ)/2, 
+			"Diff should be smaller than full state: diff=%d, full=%d", diffSize, len(fullStateSSZ))
+	})
+}
+
+// TestKMPSecurity tests the KMP algorithm for security issues
+func TestKMPSecurity(t *testing.T) {
+	t.Run("nil_pointer_handling", func(t *testing.T) {
+		// Test with nil pointers in the pattern/text
+		pattern := []*int{nil, nil, nil}
+		text := []*int{nil, nil, nil, nil, nil}
+		
+		equals := func(a, b *int) bool {
+			if a == nil && b == nil {
+				return true
+			}
+			if a == nil || b == nil {
+				return false
+			}
+			return *a == *b
+		}
+		
+		// Should not panic - result can be any integer
+		result := kmpIndex(len(pattern), text, equals)
+		_ = result // Any result is valid, just ensure no panic
+	})
+	
+	t.Run("empty_pattern_edge_case", func(t *testing.T) {
+		var pattern []*int
+		text := []*int{new(int), new(int)}
+		
+		equals := func(a, b *int) bool { return a == b }
+		
+		result := kmpIndex(0, text, equals)
+		require.Equal(t, 0, result, "Empty pattern should return 0")
+		_ = pattern // Silence unused variable warning
+	})
+	
+	t.Run("realistic_pattern_performance", func(t *testing.T) {
+		// Test with realistic sizes to ensure good performance
+		realisticSize := 100 // More realistic for validator arrays
+		pattern := make([]*int, realisticSize)
+		text := make([]*int, realisticSize*2)
+		
+		// Create realistic pattern
+		for i := range pattern {
+			val := i % 10 // More variation
+			pattern[i] = &val
+		}
+		for i := range text {
+			val := i % 10
+			text[i] = &val
+		}
+		
+		equals := func(a, b *int) bool {
+			if a == nil && b == nil {
+				return true
+			}
+			if a == nil || b == nil {
+				return false
+			}
+			return *a == *b
+		}
+		
+		start := time.Now()
+		result := kmpIndex(len(pattern), text, equals)
+		duration := time.Since(start)
+		
+		// Should complete quickly with realistic inputs
+		require.Equal(t, true, duration < time.Second, 
+			"KMP took too long: %v", duration)
+		_ = result // Any result is valid, just ensure performance is good
+	})
+}
+
+// TestConcurrencySafety tests thread safety of the hdiff operations
+func TestConcurrencySafety(t *testing.T) {
+	t.Run("concurrent_diff_creation", func(t *testing.T) {
+		source, _ := util.DeterministicGenesisStateElectra(t, 32)
+		target := source.Copy()
+		_ = target.SetSlot(source.Slot() + 1)
+		
+		const numGoroutines = 10
+		const iterations = 100
+		
+		var wg sync.WaitGroup
+		errors := make(chan error, numGoroutines*iterations)
+		
+		for i := 0; i < numGoroutines; i++ {
+			wg.Add(1)
+			go func(workerID int) {
+				defer wg.Done()
+				
+				for j := 0; j < iterations; j++ {
+					_, err := Diff(source, target)
+					if err != nil {
+						errors <- fmt.Errorf("worker %d iteration %d: %v", workerID, j, err)
+					}
+				}
+			}(i)
+		}
+		
+		wg.Wait()
+		close(errors)
+		
+		// Check for any errors
+		for err := range errors {
+			t.Error(err)
+		}
+	})
+	
+	t.Run("concurrent_diff_application", func(t *testing.T) {
+		ctx := context.Background()
+		source, _ := util.DeterministicGenesisStateElectra(t, 16)
+		target := source.Copy()
+		_ = target.SetSlot(source.Slot() + 5)
+		
+		diff, err := Diff(source, target)
+		require.NoError(t, err)
+		
+		const numGoroutines = 10
+		var wg sync.WaitGroup
+		errors := make(chan error, numGoroutines)
+		
+		for i := 0; i < numGoroutines; i++ {
+			wg.Add(1)
+			go func(workerID int) {
+				defer wg.Done()
+				
+				// Each goroutine needs its own copy of the source state
+				localSource := source.Copy()
+				_, err := ApplyDiff(ctx, localSource, diff)
+				if err != nil {
+					errors <- fmt.Errorf("worker %d: %v", workerID, err)
+				}
+			}(i)
+		}
+		
+		wg.Wait()
+		close(errors)
+		
+		// Check for any errors
+		for err := range errors {
+			t.Error(err)
+		}
+	})
+}

consensus-types/helpers/BUILD.bazel

@@ -0,0 +1,9 @@
+load("@prysm//tools/go:def.bzl", "go_library")
+
+go_library(
+    name = "go_default_library",
+    srcs = ["comparisons.go"],
+    importpath = "github.com/OffchainLabs/prysm/v6/consensus-types/helpers",
+    visibility = ["//visibility:public"],
+    deps = ["//proto/prysm/v1alpha1:go_default_library"],
+)

consensus-types/helpers/comparisons.go

@@ -0,0 +1,109 @@
+package helpers
+
+import (
+	"bytes"
+
+	ethpb "github.com/OffchainLabs/prysm/v6/proto/prysm/v1alpha1"
+)
+
+func ForksEqual(s, t *ethpb.Fork) bool {
+	if s == nil && t == nil {
+		return true
+	}
+	if s == nil || t == nil {
+		return false
+	}
+	if s.Epoch != t.Epoch {
+		return false
+	}
+	if !bytes.Equal(s.PreviousVersion, t.PreviousVersion) {
+		return false
+	}
+	return bytes.Equal(s.CurrentVersion, t.CurrentVersion)
+}
+
+func BlockHeadersEqual(s, t *ethpb.BeaconBlockHeader) bool {
+	if s == nil && t == nil {
+		return true
+	}
+	if s == nil || t == nil {
+		return false
+	}
+	if s.Slot != t.Slot {
+		return false
+	}
+	if s.ProposerIndex != t.ProposerIndex {
+		return false
+	}
+	if !bytes.Equal(s.ParentRoot, t.ParentRoot) {
+		return false
+	}
+	if !bytes.Equal(s.StateRoot, t.StateRoot) {
+		return false
+	}
+	return bytes.Equal(s.BodyRoot, t.BodyRoot)
+}
+
+func Eth1DataEqual(s, t *ethpb.Eth1Data) bool {
+	if s == nil && t == nil {
+		return true
+	}
+	if s == nil || t == nil {
+		return false
+	}
+	if !bytes.Equal(s.DepositRoot, t.DepositRoot) {
+		return false
+	}
+	if s.DepositCount != t.DepositCount {
+		return false
+	}
+	return bytes.Equal(s.BlockHash, t.BlockHash)
+}
+
+func PendingDepositsEqual(s, t *ethpb.PendingDeposit) bool {
+	if s == nil && t == nil {
+		return true
+	}
+	if s == nil || t == nil {
+		return false
+	}
+	if !bytes.Equal(s.PublicKey, t.PublicKey) {
+		return false
+	}
+	if !bytes.Equal(s.WithdrawalCredentials, t.WithdrawalCredentials) {
+		return false
+	}
+	if s.Amount != t.Amount {
+		return false
+	}
+	if !bytes.Equal(s.Signature, t.Signature) {
+		return false
+	}
+	return s.Slot == t.Slot
+}
+
+func PendingPartialWithdrawalsEqual(s, t *ethpb.PendingPartialWithdrawal) bool {
+	if s == nil && t == nil {
+		return true
+	}
+	if s == nil || t == nil {
+		return false
+	}
+	if s.Index != t.Index {
+		return false
+	}
+	if s.Amount != t.Amount {
+		return false
+	}
+	return s.WithdrawableEpoch == t.WithdrawableEpoch
+}
+
+func PendingConsolidationsEqual(s, t *ethpb.PendingConsolidation) bool {
+	if s == nil && t == nil {
+		return true
+	}
+	if s == nil || t == nil {
+		return false
+	}
+	return s.SourceIndex == t.SourceIndex && s.TargetIndex == t.TargetIndex
+}