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Heze -- Honest Validator

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

Introduction

This document represents the changes to be made in the code of an "honest validator" to implement Heze.

Configuration

Helpers

New GetInclusionListResponse

@dataclass
class GetInclusionListResponse(object):
    inclusion_list_transactions: Sequence[Transaction]

Protocols

ExecutionEngine

Note: get_inclusion_list function is added to the ExecutionEngine protocol for use as an inclusion list committee member.

The body of this function is implementation dependent. The Engine API may be used to implement it with an external execution engine.

New get_inclusion_list

get_inclusion_list returns GetInclusionListResponse with the most recent inclusion list transactions that has been built based on the latest view of the public mempool.

def get_inclusion_list(self: ExecutionEngine) -> GetInclusionListResponse:
    """
    Return ``GetInclusionListResponse`` object.
    """
    ...

Beacon chain responsibilities

All validator responsibilities remain unchanged other than those noted below.

Validator assignments

Inclusion list committee

A validator may be a member of the new inclusion list committee for a given slot. To check for inclusion list committee assignments, use get_inclusion_list_committee_assignment(state, epoch, validator_index) where epoch <= next_epoch, as inclusion list committee selection is only stable within the context of the current and next epoch.

def get_inclusion_list_committee_assignment(
    state: BeaconState, epoch: Epoch, validator_index: ValidatorIndex
) -> Optional[Slot]:
    """
    Returns the slot during the requested epoch in which the validator with
    index ``validator_index`` is a member of the inclusion list committee.
    Returns None if no assignment is found.
    """
    next_epoch = Epoch(get_current_epoch(state) + 1)
    assert epoch <= next_epoch

    start_slot = compute_start_slot_at_epoch(epoch)
    for slot in range(start_slot, start_slot + SLOTS_PER_EPOCH):
        if validator_index in get_inclusion_list_committee(state, Slot(slot)):
            return Slot(slot)
    return None

Lookahead

get_inclusion_list_committee_assignment should be called at the start of each epoch to get the assignment for the next epoch (current_epoch + 1). A validator should plan for future assignments by noting their assigned inclusion list committee slot.

Block and sidecar proposal

Constructing the BeaconBlockBody

Signed execution payload bid

Note: The only change made to signed_execution_payload_bid is to require that bid.inclusion_list_bits must satisfy is_inclusion_list_bits_inclusive() with respect to the proposer's inclusion list view, which comprises all valid and non-equivocating inclusion lists they have observed.

  • The bid.inclusion_list_bits must satisfy is_inclusion_list_bits_inclusive(get_inclusion_list_store(), state, slot - 1, bid.inclusion_list_bits, only_timely=False).
ExecutionPayload

prepare_execution_payload is updated from the Gloas specification to provide the inclusion list transactions.

Note: In this section, state is the state of the slot for the block proposal without the block yet applied. That is, state is the previous_state processed through any empty slots up to the assigned slot using process_slots(previous_state, slot).

Note: A proposer should produce an execution payload that satisfies the inclusion list constraints with respect to their inclusion list view at the time of payload construction, which comprises all valid and non-equivocating inclusion lists they have observed.

def prepare_execution_payload(
    store: Store,
    state: BeaconState,
    safe_block_hash: Hash32,
    finalized_block_hash: Hash32,
    suggested_fee_recipient: ExecutionAddress,
    execution_engine: ExecutionEngine,
) -> Optional[PayloadId]:
    parent_bid = state.latest_execution_payload_bid
    parent_root = hash_tree_root(state.latest_block_header)
    if should_extend_payload(store, parent_root):
        envelope = store.payloads[parent_root]
        # Make a copy of the state to avoid mutability issues
        state = copy(state)
        # Apply parent payload before computing withdrawals
        apply_parent_execution_payload(state, envelope.execution_requests)
        withdrawals = get_expected_withdrawals(state).withdrawals
        head_block_hash = parent_bid.block_hash
    else:
        withdrawals = state.payload_expected_withdrawals
        head_block_hash = parent_bid.parent_block_hash

    # Set the forkchoice head and initiate the payload build process
    payload_attributes = PayloadAttributes(
        timestamp=compute_time_at_slot(state, state.slot),
        prev_randao=get_randao_mix(state, get_current_epoch(state)),
        suggested_fee_recipient=suggested_fee_recipient,
        withdrawals=withdrawals,
        parent_beacon_block_root=hash_tree_root(state.latest_block_header),
        slot_number=state.slot,
        # [New in Heze:EIP7805]
        inclusion_list_transactions=get_inclusion_list_transactions(
            get_inclusion_list_store(), state, Slot(state.slot - 1), only_timely=False
        ),
    )
    return execution_engine.notify_forkchoice_updated(
        head_block_hash=head_block_hash,
        safe_block_hash=safe_block_hash,
        finalized_block_hash=finalized_block_hash,
        payload_attributes=payload_attributes,
    )

Inclusion list proposal

A validator is expected to propose a SignedInclusionList at the beginning of any slot for which get_inclusion_list_committee_assignment(state, epoch, validator_index) returns.

If a validator is in the current inclusion list committee, the validator should create and broadcast the signed_inclusion_list to the global inclusion_list subnet by get_inclusion_list_due_ms() milliseconds into the slot, built against the block for the current slot if it has been processed and confirmed as head, or against the local head returned by get_head() otherwise.

Constructing the SignedInclusionList

The validator creates the signed_inclusion_list as follows:

  • First, the validator creates the inclusion_list.
  • Set inclusion_list.slot to the assigned slot returned by get_inclusion_list_committee_assignment.
  • Set inclusion_list.validator_index to the validator's index.
  • Set inclusion_list.inclusion_list_committee_root to the hash tree root of the committee that the validator is a member of.
  • Set inclusion_list.transactions using the response from ExecutionEngine via get_inclusion_list.

After building the inclusion_list, the validator obtains a signature of the inclusion list by using:

def get_inclusion_list_signature(
    state: BeaconState, inclusion_list: InclusionList, privkey: int
) -> BLSSignature:
    domain = get_domain(
        state, DOMAIN_INCLUSION_LIST_COMMITTEE, compute_epoch_at_slot(inclusion_list.slot)
    )
    signing_root = compute_signing_root(inclusion_list, domain)
    return bls.Sign(privkey, signing_root)

Then the validator assembles signed_inclusion_list = SignedInclusionList(message=inclusion_list, signature=signature) and broadcasts it on the inclusion_list global gossip topic.