sync-protocol.md

Deneb Light Client -- Sync Protocol

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

Table of contents

• Introduction
• Helper functions
  • Modified get_lc_execution_root
  • Modified is_valid_light_client_header

Introduction

This upgrade updates light client data to include the Deneb changes to the ExecutionPayload structure. It extends the Capella Light Client specifications. The fork document explains how to upgrade existing Capella based deployments to Deneb.

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

• Full node
• Networking

Helper functions

Modified get_lc_execution_root

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

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

    # [Modified in Deneb]
    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)

    # [New in Deneb:EIP4844]
    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,
    )