# EIP-7002 -- The Beacon Chain ## Table of contents - [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) ## 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 [Capella](../../capella/beacon-chain.md) and is under active development. ## Preset ### Max operations per block | Name | Value | | - | - | | `MAX_EXECUTION_LAYER_EXITS` | `2**4` (= 16) | ## Containers ### New containers #### `ExecutionLayerExit` ```python class ExecutionLayerExit(Container): source_address: ExecutionAddress validator_pubkey: BLSPubkey ``` ### 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] exits: List[ExecutionLayerExit, MAX_EXECUTION_LAYER_EXITS] # [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 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 #### Execution payload ##### Modified `process_execution_payload` ```python def process_execution_payload(state: BeaconState, body: BeaconBlockBody, execution_engine: ExecutionEngine) -> None: payload = body.execution_payload # Verify consistency of the parent hash with respect to the previous execution payload header 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.verify_and_notify_new_payload(NewPayloadRequest(execution_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), 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_pubkeys = [v.pubkey for v in state.validators] validator_index = ValidatorIndex(validator_pubkeys.index(execution_layer_exit.validator_pubkey)) validator = state.validators[validator_index] # Verify withdrawal credentials is_execution_address = validator.withdrawal_credentials[:1] == ETH1_ADDRESS_WITHDRAWAL_PREFIX is_correct_source_address = validator.withdrawal_credentials[12:] == execution_layer_exit.source_address if not (is_execution_address and 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, 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 ```