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eth2.0-specs/specs/sharding/beacon-chain.md

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Ethereum 2.0 Sharding -- Beacon Chain changes

Notice: This document is a work-in-progress for researchers and implementers.

Table of contents

Introduction

This document describes the extensions made to the Phase 0 design of The Beacon Chain to support data sharding, based on the ideas here and more broadly here, using KZG10 commitments to commit to data to remove any need for fraud proofs (and hence, safety-critical synchrony assumptions) in the design.

Glossary

  • Data: A list of KZG points, to translate a byte string into
  • Blob: Data with commitments and meta-data, like a flattened bundle of L2 transactions.
  • Builder: Builds blobs and bids for proposal slots with fee-paying blob-headers, responsible for availability.
  • Shard proposer: Validator, taking bids for shard data opportunity, co-signs with builder to propose the blob.

Custom types

We define the following Python custom types for type hinting and readability:

Name SSZ equivalent Description
Shard uint64 A shard number
BLSCommitment Bytes48 A G1 curve point
BLSPoint uint256 A number x in the range 0 <= x < MODULUS
BuilderIndex uint64 Builder registry index

Constants

The following values are (non-configurable) constants used throughout the specification.

Misc

Name Value Notes
PRIMITIVE_ROOT_OF_UNITY 5 Primitive root of unity of the BLS12_381 (inner) modulus
DATA_AVAILABILITY_INVERSE_CODING_RATE 2**1 (= 2) Factor by which samples are extended for data availability encoding
POINTS_PER_SAMPLE uint64(2**3) (= 8) 31 * 8 = 248 bytes
MODULUS 0x73eda753299d7d483339d80809a1d80553bda402fffe5bfeffffffff00000001 (curve order of BLS12_381)

Domain types

Name Value
DOMAIN_SHARD_BLOB DomainType('0x80000000')

Shard Work Status

Name Value Notes
SHARD_WORK_UNCONFIRMED 0 Unconfirmed, nullified after confirmation time elapses
SHARD_WORK_CONFIRMED 1 Confirmed, reduced to just the commitment
SHARD_WORK_PENDING 2 Pending, a list of competing headers

Preset

Misc

Name Value Notes
MAX_SHARDS uint64(2**10) (= 1,024) Theoretical max shard count (used to determine data structure sizes)
GASPRICE_ADJUSTMENT_COEFFICIENT uint64(2**3) (= 8) Gasprice may decrease/increase by at most exp(1 / this value) per epoch
MAX_SHARD_PROPOSER_SLASHINGS 2**4 (= 16) Maximum amount of shard proposer slashing operations per block
MAX_SHARD_HEADERS_PER_SHARD 4
SHARD_STATE_MEMORY_SLOTS uint64(2**8) (= 256) Number of slots for which shard commitments and confirmation status is directly available in the state
BUILDER_REGISTRY_LIMIT uint64(2**40) (= 1,099,511,627,776) builders

Shard blob samples

Name Value Notes
MAX_SAMPLES_PER_BLOB uint64(2**11) (= 2,048) 248 * 2,048 = 507,904 bytes
TARGET_SAMPLES_PER_BLOB uint64(2**10) (= 1,024) 248 * 1,024 = 253,952 bytes

Precomputed size verification points

Name Value
G1_SETUP Type List[G1]. The G1-side trusted setup [G, G*s, G*s**2....]; note that the first point is the generator.
G2_SETUP Type List[G2]. The G2-side trusted setup [G, G*s, G*s**2....]
ROOT_OF_UNITY pow(PRIMITIVE_ROOT_OF_UNITY, (MODULUS - 1) // int(MAX_SAMPLES_PER_BLOB * POINTS_PER_SAMPLE), MODULUS)

Gwei values

Name Value Unit Description
MAX_GASPRICE Gwei(2**33) (= 8,589,934,592) Gwei Max gasprice charged for a TARGET-sized shard block
MIN_GASPRICE Gwei(2**3) (= 8) Gwei Min gasprice charged for a TARGET-sized shard block

Configuration

Name Value Notes
INITIAL_ACTIVE_SHARDS uint64(2**6) (= 64) Initial shard count

Updated containers

The following containers have updated definitions to support Sharding.

AttestationData

class AttestationData(Container):
    slot: Slot
    index: CommitteeIndex
    # LMD GHOST vote
    beacon_block_root: Root
    # FFG vote
    source: Checkpoint
    target: Checkpoint
    # Hash-tree-root of ShardBlock
    shard_blob_root: Root  # [New in Sharding]

BeaconBlockBody

class BeaconBlockBody(merge.BeaconBlockBody):  # [extends The Merge block body]
    shard_proposer_slashings: List[ShardProposerSlashing, MAX_SHARD_PROPOSER_SLASHINGS]
    shard_headers: List[SignedShardBlockHeader, MAX_SHARDS * MAX_SHARD_HEADERS_PER_SHARD]

Builder

class Builder(Container):
    pubkey: BLSPubkey
    # TODO: fields for either an expiry mechanism (refunding execution account with remaining balance) 
    #  and/or a builder-transaction mechanism.

BeaconState

class BeaconState(merge.BeaconState):
    # [Updated fields] (Warning: this changes with Altair, Sharding will rebase to use participation-flags)
    previous_epoch_attestations: List[PendingAttestation, MAX_ATTESTATIONS * SLOTS_PER_EPOCH]
    current_epoch_attestations: List[PendingAttestation, MAX_ATTESTATIONS * SLOTS_PER_EPOCH]
    # [New fields]
    # Builder registry.
    builders: List[Builder, BUILDER_REGISTRY_LIMIT]
    builder_balances: List[Gwei, BUILDER_REGISTRY_LIMIT]
    # A ring buffer of the latest slots, with information per active shard.
    shard_buffer: Vector[List[ShardWork, MAX_SHARDS], SHARD_STATE_MEMORY_SLOTS]
    shard_gasprice: uint64

New containers

DataCommitment

class DataCommitment(Container):
    # KZG10 commitment to the data
    point: BLSCommitment
    # Length of the data in samples
    length: uint64

ShardBlobBody

Unsigned shard data, bundled by a shard-builder. Unique, signing different bodies as shard proposer for the same (slot, shard) is slashable.

class ShardBlobBody(Container):
    # The actual data commitment
    commitment: DataCommitment
    # Proof that the degree < commitment.length
    degree_proof: BLSCommitment
    # The actual data. Should match the commitment and degree proof.
    data: List[BLSPoint, POINTS_PER_SAMPLE * MAX_SAMPLES_PER_BLOB]
    # Latest block root of the Beacon Chain, before shard_blob.slot
    beacon_block_root: Root
    # TODO: fee payment amount fields (EIP 1559 like)

ShardBlobBodySummary

Summary version of the ShardBlobBody, omitting the data payload, while preserving the data-commitments.

The commitments are not further collapsed to a single hash, to avoid an extra network roundtrip between proposer and builder, to include the header on-chain more quickly.

class ShardBlobBodySummary(Container):
    # The actual data commitment
    commitment: DataCommitment
    # Proof that the degree < commitment.length
    degree_proof: BLSCommitment
    # Hash-tree-root as summary of the data field
    data_root: Root
    # Latest block root of the Beacon Chain, before shard_blob.slot
    beacon_block_root: Root
    # TODO: fee payment amount fields (EIP 1559 like)

ShardBlob

ShardBlobBody wrapped with the header data that is unique to the shard blob proposal.

class ShardBlob(Container):
    slot: Slot
    shard: Shard
    # Proposer of the shard-blob
    proposer_index: ValidatorIndex
    # Builder of the data, pays data-fee to proposer
    builder_index: BuilderIndex
    # Blob contents
    body: ShardBlobBody

ShardBlobHeader

Header version of ShardBlob.

class ShardBlobHeader(Container):
    slot: Slot
    shard: Shard
    # Proposer of the shard-blob
    proposer_index: ValidatorIndex
    # Builder of the data, pays data-fee to proposer
    builder_index: BuilderIndex
    # Blob contents, without the full data
    body_summary: ShardBlobBodySummary

SignedShardBlob

Full blob data, signed by the shard builder (ensuring fee payment) and shard proposer (ensuring a single proposal).

class SignedShardBlob(Container):
    message: ShardBlob
    signature: BLSSignature

SignedShardBlobHeader

Header of the blob, the signature is equally applicable to SignedShardBlob. Shard proposers can accept SignedShardBlobHeader as a data-transaction by co-signing the header.

class SignedShardBlobHeader(Container):
    message: ShardBlobHeader
    # Signature by builder.
    # Once accepted by proposer, the signatures is the aggregate of both.
    signature: BLSSignature

PendingShardHeader

class PendingShardHeader(Container):
    # KZG10 commitment to the data
    commitment: DataCommitment
    # hash_tree_root of the ShardBlockHeader (stored so that attestations can be checked against it)
    root: Root
    # Who voted for the header
    votes: Bitlist[MAX_VALIDATORS_PER_COMMITTEE]
    # Sum of effective balances of votes
    weight: Gwei
    # When the header was last updated, as reference for weight accuracy
    update_slot: Slot

ShardBlobReference

Reference version of ShardBlobHeader, substituting the body for just a hash-tree-root.

class ShardBlobReference(Container):
    slot: Slot
    shard: Shard
    # Proposer of the shard-blob
    proposer_index: ValidatorIndex
    # Builder of the data
    builder_index: BuilderIndex
    # Blob hash-tree-root for slashing reference
    body_root: Root

ShardProposerSlashing

class ShardProposerSlashing(Container):
    slot: Slot
    shard: Shard
    proposer_index: ValidatorIndex
    builder_index_1: BuilderIndex
    builder_index_2: BuilderIndex
    body_root_1: Root
    body_root_2: Root
    signature_1: BLSSignature
    signature_2: BLSSignature

ShardWork

class ShardWork(Container):
    #  Upon confirmation the data is reduced to just the header.
    status: Union[                                                   # See Shard Work Status enum
              None,                                                  # SHARD_WORK_UNCONFIRMED
              DataCommitment,                                        # SHARD_WORK_CONFIRMED
              List[PendingShardHeader, MAX_SHARD_HEADERS_PER_SHARD]  # SHARD_WORK_PENDING
            ]

Helper functions

Misc

next_power_of_two

def next_power_of_two(x: int) -> int:
    return 2 ** ((x - 1).bit_length())

compute_previous_slot

def compute_previous_slot(slot: Slot) -> Slot:
    if slot > 0:
        return Slot(slot - 1)
    else:
        return Slot(0)

compute_updated_gasprice

def compute_updated_gasprice(prev_gasprice: Gwei, shard_block_length: uint64, adjustment_quotient: uint64) -> Gwei:
    if shard_block_length > TARGET_SAMPLES_PER_BLOB:
        delta = max(1, prev_gasprice * (shard_block_length - TARGET_SAMPLES_PER_BLOB)
                       // TARGET_SAMPLES_PER_BLOB // adjustment_quotient)
        return min(prev_gasprice + delta, MAX_GASPRICE)
    else:
        delta = max(1, prev_gasprice * (TARGET_SAMPLES_PER_BLOB - shard_block_length)
                       // TARGET_SAMPLES_PER_BLOB // adjustment_quotient)
        return max(prev_gasprice, MIN_GASPRICE + delta) - delta

compute_committee_source_epoch

def compute_committee_source_epoch(epoch: Epoch, period: uint64) -> Epoch:
    """
    Return the source epoch for computing the committee.
    """
    source_epoch = Epoch(epoch - epoch % period)
    if source_epoch >= period:
        source_epoch -= period  # `period` epochs lookahead
    return source_epoch

Beacon state accessors

Updated get_committee_count_per_slot

def get_committee_count_per_slot(state: BeaconState, epoch: Epoch) -> uint64:
    """
    Return the number of committees in each slot for the given ``epoch``.
    """
    return max(uint64(1), min(
        get_active_shard_count(state, epoch),
        uint64(len(get_active_validator_indices(state, epoch))) // SLOTS_PER_EPOCH // TARGET_COMMITTEE_SIZE,
    ))

get_active_shard_count

def get_active_shard_count(state: BeaconState, epoch: Epoch) -> uint64:
    """
    Return the number of active shards.
    Note that this puts an upper bound on the number of committees per slot.
    """
    return INITIAL_ACTIVE_SHARDS

compute_proposer_index

Updated version to get a proposer index that will only allow proposers with a certain minimum balance, ensuring that the balance is always sufficient to cover gas costs.

def compute_proposer_index(beacon_state: BeaconState,
                           indices: Sequence[ValidatorIndex],
                           seed: Bytes32,
                           min_effective_balance: Gwei = Gwei(0)) -> ValidatorIndex:
    """
    Return from ``indices`` a random index sampled by effective balance.
    """
    assert len(indices) > 0
    MAX_RANDOM_BYTE = 2**8 - 1
    i = uint64(0)
    total = uint64(len(indices))
    while True:
        candidate_index = indices[compute_shuffled_index(i % total, total, seed)]
        random_byte = hash(seed + uint_to_bytes(uint64(i // 32)))[i % 32]
        effective_balance = beacon_state.validators[candidate_index].effective_balance
        if effective_balance <= min_effective_balance:
            continue
        if effective_balance * MAX_RANDOM_BYTE >= MAX_EFFECTIVE_BALANCE * random_byte:
            return candidate_index
        i += 1

get_shard_proposer_index

def get_shard_proposer_index(beacon_state: BeaconState, slot: Slot, shard: Shard) -> ValidatorIndex:
    """
    Return the proposer's index of shard block at ``slot``.
    """
    epoch = compute_epoch_at_slot(slot)
    seed = hash(get_seed(beacon_state, epoch, DOMAIN_SHARD_BLOB) + uint_to_bytes(slot) + uint_to_bytes(shard))

    # Proposer must have sufficient balance to pay for worst case fee burn
    EFFECTIVE_BALANCE_MAX_DOWNWARD_DEVIATION = (
        EFFECTIVE_BALANCE_INCREMENT - EFFECTIVE_BALANCE_INCREMENT
        * HYSTERESIS_DOWNWARD_MULTIPLIER // HYSTERESIS_QUOTIENT
    )
    min_effective_balance = (
        beacon_state.shard_gasprice * MAX_SAMPLES_PER_BLOB // TARGET_SAMPLES_PER_BLOB
        + EFFECTIVE_BALANCE_MAX_DOWNWARD_DEVIATION
    )
    indices = get_active_validator_indices(state, epoch)
    return compute_proposer_index(beacon_state, indices, seed, min_effective_balance)

get_start_shard

def get_start_shard(state: BeaconState, slot: Slot) -> Shard:
    """
    Return the start shard at ``slot``.
    """
    epoch = compute_epoch_at_slot(Slot(_slot))
    committee_count = get_committee_count_per_slot(state, epoch)
    active_shard_count = get_active_shard_count(state, epoch)
    return committee_count * slot % active_shard_count

compute_shard_from_committee_index

def compute_shard_from_committee_index(state: BeaconState, slot: Slot, index: CommitteeIndex) -> Shard:
    active_shards = get_active_shard_count(state, compute_epoch_at_slot(slot))
    assert index < active_shards
    return Shard((index + get_start_shard(state, slot)) % active_shards)

compute_committee_index_from_shard

def compute_committee_index_from_shard(state: BeaconState, slot: Slot, shard: Shard) -> CommitteeIndex:
    epoch = compute_epoch_at_slot(slot)
    active_shards = get_active_shard_count(state, epoch)
    index = CommitteeIndex((active_shards + shard - get_start_shard(state, slot)) % active_shards)
    assert index < get_committee_count_per_slot(state, epoch)
    return index

Block processing

def process_block(state: BeaconState, block: BeaconBlock) -> None:
    process_block_header(state, block)
    process_randao(state, block.body)
    process_eth1_data(state, block.body)
    process_operations(state, block.body)  # [Modified in Sharding]
    process_sync_aggregate(state, block.body.sync_aggregate)
    # is_execution_enabled is omitted, execution is enabled by default. 
    process_execution_payload(state, block.body.execution_payload, EXECUTION_ENGINE)

Operations

def process_operations(state: BeaconState, body: BeaconBlockBody) -> None:
    # Verify that outstanding deposits are processed up to the maximum number of deposits
    assert len(body.deposits) == min(MAX_DEPOSITS, state.eth1_data.deposit_count - state.eth1_deposit_index)

    def for_ops(operations: Sequence[Any], fn: Callable[[BeaconState, Any], None]) -> None:
        for operation in operations:
            fn(state, operation)

    for_ops(body.proposer_slashings, process_proposer_slashing)
    for_ops(body.attester_slashings, process_attester_slashing)
    # New shard proposer slashing processing
    for_ops(body.shard_proposer_slashings, process_shard_proposer_slashing)
    # Limit is dynamic based on active shard count
    assert len(body.shard_headers) <= MAX_SHARD_HEADERS_PER_SHARD * get_active_shard_count(state, get_current_epoch(state))
    for_ops(body.shard_headers, process_shard_header)
    # New attestation processing
    for_ops(body.attestations, process_attestation)
    for_ops(body.deposits, process_deposit)
    for_ops(body.voluntary_exits, process_voluntary_exit)
Extended Attestation processing
def process_attestation(state: BeaconState, attestation: Attestation) -> None:
    altair.process_attestation(state, attestation)
    update_pending_shard_work(state, attestation)

def update_pending_shard_work(state: BeaconState, attestation: Attestation) -> None:
    attestation_shard = compute_shard_from_committee_index(
        state,
        attestation.data.slot,
        attestation.data.index,
    )
    buffer_index = attestation.data.slot % SHARD_STATE_MEMORY_SLOTS
    committee_work = state.shard_buffer[buffer_index][attestation_shard]

    # Skip attestation vote accounting if the header is not pending
    if committee_work.status.selector != SHARD_WORK_PENDING:
        # TODO In Altair: set participation bit flag, if attestation matches winning header.
        return

    current_headers: Sequence[PendingShardHeader] = committee_work.status.value

    # Find the corresponding header, abort if it cannot be found
    header_index = [header.root for header in current_headers].index(attestation.data.shard_blob_root)

    pending_header: PendingShardHeader = current_headers[header_index]
    full_committee = get_beacon_committee(state, attestation.data.slot, attestation.data.index)

    # The weight may be outdated if it is not the initial weight, and from a previous epoch
    if pending_header.weight != 0 and compute_epoch_at_slot(pending_header.update_slot) < get_current_epoch(state):
        pending_header.weight = sum(state.validators[index].effective_balance for index, bit
                                    in zip(full_committee, pending_header.votes) if bit)

    pending_header.update_slot = state.slot

    full_committee_balance = Gwei(0)
    # Update votes bitfield in the state, update weights
    for i, bit in enumerate(attestation.aggregation_bits):
        weight = state.validators[full_committee[i]].effective_balance
        full_committee_balance += weight
        if bit:
            if not pending_header.votes[i]:
                pending_header.weight += weight
                pending_header.votes[i] = True

    # Check if the PendingShardHeader is eligible for expedited confirmation, requiring 2/3 of balance attesting
    if pending_header.weight * 3 >= full_committee_balance * 2:
        # TODO In Altair: set participation bit flag for voters of this early winning header
        if pending_header.commitment == DataCommitment():
            # The committee voted to not confirm anything
            state.shard_buffer[buffer_index][attestation_shard].status.change(
                selector=SHARD_WORK_UNCONFIRMED,
                value=None,
            )
        else:
            state.shard_buffer[buffer_index][attestation_shard].status.change(
                selector=SHARD_WORK_CONFIRMED,
                value=pending_header.commitment,
            )

charge_builder

def charge_builder(state: BeaconState, index: BuilderIndex, fee: Gwei) -> None:
    """
    Decrease the builder balance at index ``index`` by ``fee``, with underflow check.
    """
    assert state.builder_balances[index] >= fee
    state.builder_balances[index] -= fee
process_shard_header
def process_shard_header(state: BeaconState, signed_header: SignedShardBlobHeader) -> None:
    header: ShardBlobHeader = signed_header.message
    slot = header.slot
    shard = header.shard

    # Verify the header is not 0, and not from the future.
    assert Slot(0) < slot <= state.slot
    header_epoch = compute_epoch_at_slot(slot)
    # Verify that the header is within the processing time window
    assert header_epoch in [get_previous_epoch(state), get_current_epoch(state)]
    # Verify that the shard is active
    assert shard < get_active_shard_count(state, header_epoch)
    # Verify that the block root matches,
    # to ensure the header will only be included in this specific Beacon Chain sub-tree.
    assert header.body_summary.beacon_block_root == get_block_root_at_slot(state, slot - 1)

    # Check that this data is still pending
    committee_work = state.shard_buffer[slot % SHARD_STATE_MEMORY_SLOTS][shard]
    assert committee_work.status.selector == SHARD_WORK_PENDING

    # Check that this header is not yet in the pending list
    current_headers: List[PendingShardHeader, MAX_SHARD_HEADERS_PER_SHARD] = committee_work.status.value
    header_root = hash_tree_root(header)
    assert header_root not in [pending_header.root for pending_header in current_headers]

    # Verify proposer matches
    assert header.proposer_index == get_shard_proposer_index(state, slot, shard)

    # Verify builder and proposer aggregate signature
    blob_signing_root = compute_signing_root(header, get_domain(state, DOMAIN_SHARD_BLOB))
    builder_pubkey = state.builders[header.builder_index].pubkey
    proposer_pubkey = state.validators[header.proposer_index].pubkey
    assert bls.FastAggregateVerify([builder_pubkey, proposer_pubkey], blob_signing_root, signed_header.signature)

    # Verify the length by verifying the degree.
    body_summary = header.body_summary
    if body_summary.commitment.length == 0:
        assert body_summary.degree_proof == G1_SETUP[0]
    assert (
        bls.Pairing(body_summary.degree_proof, G2_SETUP[0])
        == bls.Pairing(body_summary.commitment.point, G2_SETUP[-body_summary.commitment.length])
    )

    # Charge builder, with hard balance requirement
    fee = Gwei(123)  # TODO EIP 1559 like fee? Burn some of it?
    charge_builder(state, header.builder_index, fee)
    # TODO: proposer is charged for confirmed headers (see charge_confirmed_shard_fees).
    #  Need to align incentive, so proposer does not gain from including unconfirmed headers
    increase_balance(state, blob_header.proposer_index, fee)

    # Initialize the pending header
    index = compute_committee_index_from_shard(state, slot, shard)
    committee_length = len(get_beacon_committee(state, slot, index))
    initial_votes = Bitlist[MAX_VALIDATORS_PER_COMMITTEE]([0] * committee_length)
    pending_header = PendingShardHeader(
        commitment=blob_summary.commitment,
        root=header_root,
        votes=initial_votes,
        weight=0,
        update_slot=state.slot,
    )

    # Include it in the pending list
    current_headers.append(pending_header)

The degree proof works as follows. For a block B with length l (so l values in [0...l - 1], seen as a polynomial B(X) which takes these values), the length proof is the commitment to the polynomial B(X) * X**(MAX_DEGREE + 1 - l), where MAX_DEGREE is the maximum power of s available in the setup, which is MAX_DEGREE = len(G2_SETUP) - 1. The goal is to ensure that a proof can only be constructed if deg(B) < l (there are not hidden higher-order terms in the polynomial, which would thwart reconstruction).

process_shard_proposer_slashing
def process_shard_proposer_slashing(state: BeaconState, proposer_slashing: ShardProposerSlashing) -> None:
    # Verify the headers are different
    assert proposer_slashing.body_root_1 != proposer_slashing.body_root_2

    slot = proposer_slashing.slot
    shard = proposer_slashing.shard
    proposer_index = proposer_slashing.proposer_index

    # Verify the proposer is slashable
    proposer = state.validators[proposer_index]
    assert is_slashable_validator(proposer, get_current_epoch(state))

    reference_1 = ShardBlobReference(slot=slot, shard=shard,
                                     proposer_index=proposer_index,
                                     builder_index=proposer_slashing.builder_index_1,
                                     body_root= proposer_slashing.body_root_1)
    reference_2 = ShardBlobReference(slot=slot, shard=shard,
                                     proposer_index=proposer_index,
                                     builder_index=proposer_slashing.builder_index_1,
                                     body_root= proposer_slashing.body_root_2)
    # The builders are not slashed, the proposer co-signed with them
    builder_pubkey_1 = state.builders[proposer_slashing.builder_index_1].pubkey
    builder_pubkey_2 = state.builders[proposer_slashing.builder_index_2].pubkey
    domain = get_domain(state, DOMAIN_SHARD_PROPOSER, compute_epoch_at_slot(slot))
    signing_root_1 = compute_signing_root(reference_1, domain)
    signing_root_2 = compute_signing_root(reference_2, domain)
    assert bls.FastAggregateVerify([builder_pubkey_1, proposer.pubkey], signing_root_1, proposer_slashing.signature_1)
    assert bls.FastAggregateVerify([builder_pubkey_2, proposer.pubkey], signing_root_2, proposer_slashing.signature_2)

    slash_validator(state, proposer_index)

Epoch transition

This epoch transition overrides the Merge epoch transition:

def process_epoch(state: BeaconState) -> None:
    # Sharding pre-processing
    process_pending_shard_confirmations(state)
    charge_confirmed_shard_fees(state)
    reset_pending_shard_work(state)

    # Base functionality
    process_justification_and_finalization(state)
    process_inactivity_updates(state)
    process_rewards_and_penalties(state)
    process_registry_updates(state)
    process_slashings(state)
    process_eth1_data_reset(state)
    process_effective_balance_updates(state)
    process_slashings_reset(state)
    process_randao_mixes_reset(state)
    process_historical_roots_update(state)
    process_participation_flag_updates(state)
    process_sync_committee_updates(state)

process_pending_shard_confirmations

def process_pending_shard_confirmations(state: BeaconState) -> None:
    # Pending header processing applies to the previous epoch.
    # Skip if `GENESIS_EPOCH` because no prior epoch to process.
    if get_current_epoch(state) == GENESIS_EPOCH:
        return

    previous_epoch = get_previous_epoch(state)
    previous_epoch_start_slot = compute_start_slot_at_epoch(previous_epoch)

    # Mark stale headers as unconfirmed
    for slot in range(previous_epoch_start_slot, previous_epoch_start_slot + SLOTS_PER_EPOCH):
        buffer_index = slot % SHARD_STATE_MEMORY_SLOTS
        for shard_index in range(len(state.shard_buffer[buffer_index])):
            committee_work = state.shard_buffer[buffer_index][shard_index]
            if committee_work.status.selector == SHARD_WORK_PENDING:
                winning_header = max(committee_work.status.value, key=lambda header: header.weight)
                # TODO In Altair: set participation bit flag of voters for winning header
                if winning_header.commitment == DataCommitment():
                    committee_work.status.change(selector=SHARD_WORK_UNCONFIRMED, value=None)
                else:
                    committee_work.status.change(selector=SHARD_WORK_CONFIRMED, value=winning_header.commitment)

charge_confirmed_shard_fees

def charge_confirmed_shard_fees(state: BeaconState) -> None:
    new_gasprice = state.shard_gasprice
    previous_epoch = get_previous_epoch(state)
    previous_epoch_start_slot = compute_start_slot_at_epoch(previous_epoch)
    adjustment_quotient = (
        get_active_shard_count(state, previous_epoch)
        * SLOTS_PER_EPOCH * GASPRICE_ADJUSTMENT_COEFFICIENT
    )
    # Iterate through confirmed shard-headers
    for slot in range(previous_epoch_start_slot, previous_epoch_start_slot + SLOTS_PER_EPOCH):
        buffer_index = slot % SHARD_STATE_MEMORY_SLOTS
        for shard_index in range(len(state.shard_buffer[buffer_index])):
            committee_work = state.shard_buffer[buffer_index][shard_index]
            if committee_work.status.selector == SHARD_WORK_CONFIRMED:
                commitment: DataCommitment = committee_work.status.value
                # Charge EIP 1559 fee
                proposer = get_shard_proposer_index(state, slot, Shard(shard_index))
                fee = (
                    (state.shard_gasprice * commitment.length)
                    // TARGET_SAMPLES_PER_BLOB
                )
                decrease_balance(state, proposer, fee)

                # Track updated gas price
                new_gasprice = compute_updated_gasprice(
                    new_gasprice,
                    commitment.length,
                    adjustment_quotient,
                )
    state.shard_gasprice = new_gasprice

reset_pending_shard_work

def reset_pending_shard_work(state: BeaconState) -> None:
    # Add dummy "empty" PendingShardHeader (default vote if no shard header is available)
    next_epoch = get_current_epoch(state) + 1
    next_epoch_start_slot = compute_start_slot_at_epoch(next_epoch)
    committees_per_slot = get_committee_count_per_slot(state, next_epoch)
    active_shards = get_active_shard_count(state, next_epoch)

    for slot in range(next_epoch_start_slot, next_epoch_start_slot + SLOTS_PER_EPOCH):
        buffer_index = slot % SHARD_STATE_MEMORY_SLOTS
        
        # Reset the shard work tracking
        state.shard_buffer[buffer_index] = [ShardWork() for _ in range(active_shards)]

        start_shard = get_start_shard(state, slot)
        for committee_index in range(committees_per_slot):
            shard = (start_shard + committee_index) % active_shards
            # a committee is available, initialize a pending shard-header list
            committee_length = len(get_beacon_committee(state, slot, CommitteeIndex(committee_index)))
            state.shard_buffer[buffer_index][shard].status.change(
                selector=SHARD_WORK_PENDING,
                value=List[PendingShardHeader, MAX_SHARD_HEADERS_PER_SHARD](
                    PendingShardHeader(
                        commitment=DataCommitment(),
                        root=Root(),
                        votes=Bitlist[MAX_VALIDATORS_PER_COMMITTEE]([0] * committee_length),
                        weight=0,
                        update_slot=slot,
                    )
                )
            )
        # a shard without committee available defaults to SHARD_WORK_UNCONFIRMED.