eth2.0-specs/specs/deneb/light-client/sync-protocol.md

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# Deneb Light Client -- Sync Protocol
**Notice**: This document is a work-in-progress for researchers and implementers.
## Table of contents
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- [Introduction](#introduction)
- [Helper functions](#helper-functions)
- [Modified `get_lc_execution_root`](#modified-get_lc_execution_root)
- [Modified `is_valid_light_client_header`](#modified-is_valid_light_client_header)
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## Introduction
This upgrade updates light client data to include the Deneb changes to the [`ExecutionPayload`](../beacon-chain.md) structure. It extends the [Capella Light Client specifications](../../capella/light-client/sync-protocol.md). The [fork document](./fork.md) explains how to upgrade existing Capella based deployments to Deneb.
Additional documents describes the impact of the upgrade on certain roles:
- [Full node](./full-node.md)
- [Networking](./p2p-interface.md)
## Helper functions
### Modified `get_lc_execution_root`
```python
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`
```python
def is_valid_light_client_header(header: LightClientHeader) -> bool:
epoch = compute_epoch_at_slot(header.beacon.slot)
# [New in Deneb]
if epoch < DENEB_FORK_EPOCH:
if header.execution.data_gas_used != uint64(0) or header.execution.excess_data_gas != uint64(0):
return False
if epoch < CAPELLA_FORK_EPOCH:
return (
header.execution == ExecutionPayloadHeader()
and header.execution_branch == [Bytes32() for _ in range(floorlog2(EXECUTION_PAYLOAD_INDEX))]
)
return is_valid_merkle_branch(
leaf=get_lc_execution_root(header),
branch=header.execution_branch,
depth=floorlog2(EXECUTION_PAYLOAD_INDEX),
index=get_subtree_index(EXECUTION_PAYLOAD_INDEX),
root=header.beacon.body_root,
)
```