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Electra Light Client -- Sync Protocol

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

Introduction
Custom types
Constants
- Frozen constants
- New constants
Helper functions

Introduction

This upgrade updates light client data to include the Electra changes to the ExecutionPayload structure and to the generalized indices of surrounding containers. It extends the Deneb Light Client specifications. The fork document explains how to upgrade existing Deneb based deployments to Electra.

Additional documents describes the impact of the upgrade on certain roles:

Custom types

Name	SSZ equivalent	Description
`FinalityBranch`	`Vector[Bytes32, floorlog2(FINALIZED_ROOT_GINDEX_ELECTRA)]`	Merkle branch of `finalized_checkpoint.root` within `BeaconState`
`CurrentSyncCommitteeBranch`	`Vector[Bytes32, floorlog2(CURRENT_SYNC_COMMITTEE_GINDEX_ELECTRA)]`	Merkle branch of `current_sync_committee` within `BeaconState`
`NextSyncCommitteeBranch`	`Vector[Bytes32, floorlog2(NEXT_SYNC_COMMITTEE_GINDEX_ELECTRA)]`	Merkle branch of `next_sync_committee` within `BeaconState`

Constants

Frozen constants

Existing GeneralizedIndex constants are frozen at their Altair values.

Name	Value
`FINALIZED_ROOT_GINDEX`	`get_generalized_index(altair.BeaconState, 'finalized_checkpoint', 'root')` (= 105)
`CURRENT_SYNC_COMMITTEE_GINDEX`	`get_generalized_index(altair.BeaconState, 'current_sync_committee')` (= 54)
`NEXT_SYNC_COMMITTEE_GINDEX`	`get_generalized_index(altair.BeaconState, 'next_sync_committee')` (= 55)

New constants

Name	Value
`FINALIZED_ROOT_GINDEX_ELECTRA`	`get_generalized_index(BeaconState, 'finalized_checkpoint', 'root')` (= 169)
`CURRENT_SYNC_COMMITTEE_GINDEX_ELECTRA`	`get_generalized_index(BeaconState, 'current_sync_committee')` (= 86)
`NEXT_SYNC_COMMITTEE_GINDEX_ELECTRA`	`get_generalized_index(BeaconState, 'next_sync_committee')` (= 87)

Helper functions

Modified `finalized_root_gindex_at_slot`

def finalized_root_gindex_at_slot(slot: Slot) -> GeneralizedIndex:
    epoch = compute_epoch_at_slot(slot)

    # [Modified in Electra]
    if epoch >= ELECTRA_FORK_EPOCH:
        return FINALIZED_ROOT_GINDEX_ELECTRA
    return FINALIZED_ROOT_GINDEX

Modified `current_sync_committee_gindex_at_slot`

def current_sync_committee_gindex_at_slot(slot: Slot) -> GeneralizedIndex:
    epoch = compute_epoch_at_slot(slot)

    # [Modified in Electra]
    if epoch >= ELECTRA_FORK_EPOCH:
        return CURRENT_SYNC_COMMITTEE_GINDEX_ELECTRA
    return CURRENT_SYNC_COMMITTEE_GINDEX

Modified `next_sync_committee_gindex_at_slot`

def next_sync_committee_gindex_at_slot(slot: Slot) -> GeneralizedIndex:
    epoch = compute_epoch_at_slot(slot)

    # [Modified in Electra]
    if epoch >= ELECTRA_FORK_EPOCH:
        return NEXT_SYNC_COMMITTEE_GINDEX_ELECTRA
    return NEXT_SYNC_COMMITTEE_GINDEX

Modified `get_lc_execution_root`

def get_lc_execution_root(header: LightClientHeader) -> Root:
    epoch = compute_epoch_at_slot(header.beacon.slot)

    # [New in Electra]
    if epoch >= ELECTRA_FORK_EPOCH:
        return hash_tree_root(header.execution)

    # [Modified in Electra]
    if epoch >= DENEB_FORK_EPOCH:
        execution_header = deneb.ExecutionPayloadHeader(
            parent_hash=header.execution.parent_hash,
            fee_recipient=header.execution.fee_recipient,
            state_root=header.execution.state_root,
            receipts_root=header.execution.receipts_root,
            logs_bloom=header.execution.logs_bloom,
            prev_randao=header.execution.prev_randao,
            block_number=header.execution.block_number,
            gas_limit=header.execution.gas_limit,
            gas_used=header.execution.gas_used,
            timestamp=header.execution.timestamp,
            extra_data=header.execution.extra_data,
            base_fee_per_gas=header.execution.base_fee_per_gas,
            block_hash=header.execution.block_hash,
            transactions_root=header.execution.transactions_root,
            withdrawals_root=header.execution.withdrawals_root,
            blob_gas_used=header.execution.blob_gas_used,
            excess_blob_gas=header.execution.excess_blob_gas,
        )
        return hash_tree_root(execution_header)

    if epoch >= CAPELLA_FORK_EPOCH:
        execution_header = capella.ExecutionPayloadHeader(
            parent_hash=header.execution.parent_hash,
            fee_recipient=header.execution.fee_recipient,
            state_root=header.execution.state_root,
            receipts_root=header.execution.receipts_root,
            logs_bloom=header.execution.logs_bloom,
            prev_randao=header.execution.prev_randao,
            block_number=header.execution.block_number,
            gas_limit=header.execution.gas_limit,
            gas_used=header.execution.gas_used,
            timestamp=header.execution.timestamp,
            extra_data=header.execution.extra_data,
            base_fee_per_gas=header.execution.base_fee_per_gas,
            block_hash=header.execution.block_hash,
            transactions_root=header.execution.transactions_root,
            withdrawals_root=header.execution.withdrawals_root,
        )
        return hash_tree_root(execution_header)

    return Root()

Modified `is_valid_light_client_header`

def is_valid_light_client_header(header: LightClientHeader) -> bool:
    epoch = compute_epoch_at_slot(header.beacon.slot)

    if epoch < DENEB_FORK_EPOCH:
        if header.execution.blob_gas_used != uint64(0) or header.execution.excess_blob_gas != uint64(0):
            return False

    if epoch < CAPELLA_FORK_EPOCH:
        return (
            header.execution == ExecutionPayloadHeader()
            and header.execution_branch == ExecutionBranch()
        )

    return is_valid_merkle_branch(
        leaf=get_lc_execution_root(header),
        branch=header.execution_branch,
        depth=floorlog2(EXECUTION_PAYLOAD_GINDEX),
        index=get_subtree_index(EXECUTION_PAYLOAD_GINDEX),
        root=header.beacon.body_root,
    )

7.1 KiB Raw Blame History

Electra Light Client -- Sync Protocol

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