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eth2.0-specs/specs/_features/eip7002/beacon-chain.md

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# EIP-7002 -- The Beacon Chain
## Table of contents
<!-- TOC -->
<!-- START doctoc generated TOC please keep comment here to allow auto update -->
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- [Introduction](#introduction)
- [Preset](#preset)
- [Max operations per block](#max-operations-per-block)
- [Containers](#containers)
- [New containers](#new-containers)
- [`ExecutionLayerExit`](#executionlayerexit)
- [Extended Containers](#extended-containers)
- [`ExecutionPayload`](#executionpayload)
- [`ExecutionPayloadHeader`](#executionpayloadheader)
- [`BeaconState`](#beaconstate)
- [Beacon chain state transition function](#beacon-chain-state-transition-function)
- [Block processing](#block-processing)
- [Execution payload](#execution-payload)
- [Modified `process_execution_payload`](#modified-process_execution_payload)
- [Operations](#operations)
- [Modified `process_operations`](#modified-process_operations)
- [New `process_execution_layer_exit`](#new-process_execution_layer_exit)
- [Testing](#testing)
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## Introduction
This is the beacon chain specification of the execution layer triggerable exits feature.
This mechanism relies on the changes proposed by [EIP-7002](http://eips.ethereum.org/EIPS/eip-7002).
*Note:* This specification is built upon [Deneb](../../deneb/beacon-chain.md) and is under active development.
## Preset
### Max operations per block
| Name | Value |
| - | - |
| `MAX_EXITS_PER_BLOCK` | `2**4` (= 16) |
## Containers
### New containers
#### `ExecutionLayerExit`
```python
class ExecutionLayerExit(Container):
source_address: ExecutionAddress
validator_index: ValidatorIndex
```
### Extended Containers
#### `ExecutionPayload`
```python
class ExecutionPayload(Container):
# Execution block header fields
parent_hash: Hash32
fee_recipient: ExecutionAddress
state_root: Bytes32
receipts_root: Bytes32
logs_bloom: ByteVector[BYTES_PER_LOGS_BLOOM]
prev_randao: Bytes32
block_number: uint64
gas_limit: uint64
gas_used: uint64
timestamp: uint64
extra_data: ByteList[MAX_EXTRA_DATA_BYTES]
base_fee_per_gas: uint256
# Extra payload fields
block_hash: Hash32
transactions: List[Transaction, MAX_TRANSACTIONS_PER_PAYLOAD]
withdrawals: List[Withdrawal, MAX_WITHDRAWALS_PER_PAYLOAD]
excess_data_gas: uint256
exits: List[ExecutionLayerExit, MAX_EXITS_PER_BLOCK] # [New in EIP7002]
```
#### `ExecutionPayloadHeader`
```python
class ExecutionPayloadHeader(Container):
# Execution block header fields
parent_hash: Hash32
fee_recipient: ExecutionAddress
state_root: Bytes32
receipts_root: Bytes32
logs_bloom: ByteVector[BYTES_PER_LOGS_BLOOM]
prev_randao: Bytes32
block_number: uint64
gas_limit: uint64
gas_used: uint64
timestamp: uint64
extra_data: ByteList[MAX_EXTRA_DATA_BYTES]
base_fee_per_gas: uint256
# Extra payload fields
block_hash: Hash32
transactions_root: Root
withdrawals_root: Root
excess_data_gas: uint256
exits_root: Root # [New in EIP7002]
```
#### `BeaconState`
```python
class BeaconState(Container):
# Versioning
genesis_time: uint64
genesis_validators_root: Root
slot: Slot
fork: Fork
# History
latest_block_header: BeaconBlockHeader
block_roots: Vector[Root, SLOTS_PER_HISTORICAL_ROOT]
state_roots: Vector[Root, SLOTS_PER_HISTORICAL_ROOT]
historical_roots: List[Root, HISTORICAL_ROOTS_LIMIT]
# Eth1
eth1_data: Eth1Data
eth1_data_votes: List[Eth1Data, EPOCHS_PER_ETH1_VOTING_PERIOD * SLOTS_PER_EPOCH]
eth1_deposit_index: uint64
# Registry
validators: List[Validator, VALIDATOR_REGISTRY_LIMIT]
balances: List[Gwei, VALIDATOR_REGISTRY_LIMIT]
# Randomness
randao_mixes: Vector[Bytes32, EPOCHS_PER_HISTORICAL_VECTOR]
# Slashings
slashings: Vector[Gwei, EPOCHS_PER_SLASHINGS_VECTOR] # Per-epoch sums of slashed effective balances
# Participation
previous_epoch_participation: List[ParticipationFlags, VALIDATOR_REGISTRY_LIMIT]
current_epoch_participation: List[ParticipationFlags, VALIDATOR_REGISTRY_LIMIT]
# Finality
justification_bits: Bitvector[JUSTIFICATION_BITS_LENGTH] # Bit set for every recent justified epoch
previous_justified_checkpoint: Checkpoint
current_justified_checkpoint: Checkpoint
finalized_checkpoint: Checkpoint
# Inactivity
inactivity_scores: List[uint64, VALIDATOR_REGISTRY_LIMIT]
# Sync
current_sync_committee: SyncCommittee
next_sync_committee: SyncCommittee
# Execution
latest_execution_payload_header: ExecutionPayloadHeader # [Modified in EIP7002]
# Withdrawals
next_withdrawal_index: WithdrawalIndex
next_withdrawal_validator_index: ValidatorIndex
# Deep history valid from Capella onwards
historical_summaries: List[HistoricalSummary, HISTORICAL_ROOTS_LIMIT]
```
## Beacon chain state transition function
### Block processing
```python
def process_block(state: BeaconState, block: BeaconBlock) -> None:
process_block_header(state, block)
if is_execution_enabled(state, block.body):
process_withdrawals(state, block.body.execution_payload)
process_execution_payload(state, block.body.execution_payload, EXECUTION_ENGINE) # [Modified in EIP7002]
process_randao(state, block.body)
process_eth1_data(state, block.body)
process_operations(state, block.body) # [Modified in EIP7002]
process_sync_aggregate(state, block.body.sync_aggregate)
process_blob_kzg_commitments(block.body)
```
#### Execution payload
##### Modified `process_execution_payload`
```python
def process_execution_payload(state: BeaconState, payload: ExecutionPayload, execution_engine: ExecutionEngine) -> None:
# Verify consistency of the parent hash with respect to the previous execution payload header
if is_merge_transition_complete(state):
assert payload.parent_hash == state.latest_execution_payload_header.block_hash
# Verify prev_randao
assert payload.prev_randao == get_randao_mix(state, get_current_epoch(state))
# Verify timestamp
assert payload.timestamp == compute_timestamp_at_slot(state, state.slot)
# Verify the execution payload is valid
assert execution_engine.notify_new_payload(payload)
# Cache execution payload header
state.latest_execution_payload_header = ExecutionPayloadHeader(
parent_hash=payload.parent_hash,
fee_recipient=payload.fee_recipient,
state_root=payload.state_root,
receipts_root=payload.receipts_root,
logs_bloom=payload.logs_bloom,
prev_randao=payload.prev_randao,
block_number=payload.block_number,
gas_limit=payload.gas_limit,
gas_used=payload.gas_used,
timestamp=payload.timestamp,
extra_data=payload.extra_data,
base_fee_per_gas=payload.base_fee_per_gas,
block_hash=payload.block_hash,
transactions_root=hash_tree_root(payload.transactions),
withdrawals_root=hash_tree_root(payload.withdrawals),
excess_data_gas=payload.excess_data_gas,
exits_root=hash_tree_root(payload.exits), # [New in EIP7002]
)
```
#### Operations
##### Modified `process_operations`
*Note*: The function `process_operations` is modified to process `ExecutionLayerExit` operations included in the block.
```python
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)
for_ops(body.attestations, process_attestation)
for_ops(body.deposits, process_deposit)
for_ops(body.voluntary_exits, process_voluntary_exit)
for_ops(body.execution_payload.exits, process_execution_layer_exit) # [New in EIP7002]
for_ops(body.bls_to_execution_changes, process_bls_to_execution_change)
```
##### New `process_execution_layer_exit`
```python
def process_execution_layer_exit(state: BeaconState, execution_layer_exit: ExecutionLayerExit) -> None:
validator = state.validators[execution_layer_exit.validator_index]
# Verify withdrawal credentials
is_correct_source_address = (
validator.withdrawal_credentials[:1] == ETH1_ADDRESS_WITHDRAWAL_PREFIX
and validator.withdrawal_credentials[12:] == execution_layer_exit.source_address
)
if not is_correct_source_address:
return
# Verify the validator is active
if not is_active_validator(validator, get_current_epoch(state)):
return
# Verify exit has not been initiated
if validator.exit_epoch != FAR_FUTURE_EPOCH:
return
# Verify the validator has been active long enough
if get_current_epoch(state) < validator.activation_epoch + SHARD_COMMITTEE_PERIOD:
return
# Initiate exit
initiate_validator_exit(state, execution_layer_exit.validator_index)
```
## Testing
*Note*: The function `initialize_beacon_state_from_eth1` is modified for pure EIP-7002 testing only.
Modifications include:
1. Use `EIP7002_FORK_VERSION` as the previous and current fork version.
2. Utilize the EIP-7002 `BeaconBlockBody` when constructing the initial `latest_block_header`.
```python
def initialize_beacon_state_from_eth1(eth1_block_hash: Hash32,
eth1_timestamp: uint64,
deposits: Sequence[Deposit],
execution_payload_header: ExecutionPayloadHeader=ExecutionPayloadHeader()
) -> BeaconState:
fork = Fork(
previous_version=EIP7002_FORK_VERSION, # [Modified in EIP7002] for testing only
current_version=EIP7002_FORK_VERSION, # [Modified in EIP7002]
epoch=GENESIS_EPOCH,
)
state = BeaconState(
genesis_time=eth1_timestamp + GENESIS_DELAY,
fork=fork,
eth1_data=Eth1Data(block_hash=eth1_block_hash, deposit_count=uint64(len(deposits))),
latest_block_header=BeaconBlockHeader(body_root=hash_tree_root(BeaconBlockBody())),
randao_mixes=[eth1_block_hash] * EPOCHS_PER_HISTORICAL_VECTOR, # Seed RANDAO with Eth1 entropy
)
# Process deposits
leaves = list(map(lambda deposit: deposit.data, deposits))
for index, deposit in enumerate(deposits):
deposit_data_list = List[DepositData, 2**DEPOSIT_CONTRACT_TREE_DEPTH](*leaves[:index + 1])
state.eth1_data.deposit_root = hash_tree_root(deposit_data_list)
process_deposit(state, deposit)
# Process activations
for index, validator in enumerate(state.validators):
balance = state.balances[index]
validator.effective_balance = min(balance - balance % EFFECTIVE_BALANCE_INCREMENT, MAX_EFFECTIVE_BALANCE)
if validator.effective_balance == MAX_EFFECTIVE_BALANCE:
validator.activation_eligibility_epoch = GENESIS_EPOCH
validator.activation_epoch = GENESIS_EPOCH
# Set genesis validators root for domain separation and chain versioning
state.genesis_validators_root = hash_tree_root(state.validators)
# Fill in sync committees
# Note: A duplicate committee is assigned for the current and next committee at genesis
state.current_sync_committee = get_next_sync_committee(state)
state.next_sync_committee = get_next_sync_committee(state)
# Initialize the execution payload header
state.latest_execution_payload_header = execution_payload_header
return state
```
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