# The Merge -- The Beacon Chain **Notice**: This document is a work-in-progress for researchers and implementers. ## Table of contents - [Introduction](#introduction) - [Custom types](#custom-types) - [Preset](#preset) - [Execution](#execution) - [Updated penalty values](#updated-penalty-values) - [Configuration](#configuration) - [Transition settings](#transition-settings) - [Containers](#containers) - [Extended containers](#extended-containers) - [`BeaconBlockBody`](#beaconblockbody) - [`BeaconState`](#beaconstate) - [New containers](#new-containers) - [`ExecutionPayload`](#executionpayload) - [`ExecutionPayloadHeader`](#executionpayloadheader) - [Helper functions](#helper-functions) - [Predicates](#predicates) - [`is_merge_transition_complete`](#is_merge_transition_complete) - [`is_merge_transition_block`](#is_merge_transition_block) - [`is_execution_enabled`](#is_execution_enabled) - [Misc](#misc) - [`compute_timestamp_at_slot`](#compute_timestamp_at_slot) - [Beacon state accessors](#beacon-state-accessors) - [Modified `get_inactivity_penalty_deltas`](#modified-get_inactivity_penalty_deltas) - [Beacon state mutators](#beacon-state-mutators) - [Modified `slash_validator`](#modified-slash_validator) - [Beacon chain state transition function](#beacon-chain-state-transition-function) - [Execution engine](#execution-engine) - [`execute_payload`](#execute_payload) - [Block processing](#block-processing) - [Execution payload](#execution-payload) - [`process_execution_payload`](#process_execution_payload) - [Epoch processing](#epoch-processing) - [Slashings](#slashings) - [Testing](#testing) ## Introduction This upgrade adds transaction execution to the beacon chain as part of the Merge fork. Additionally, this upgrade introduces the following minor changes: * Penalty parameter updates to their planned maximally punitive values ## Custom types *Note*: The `Transaction` type is a stub which is not final. | Name | SSZ equivalent | Description | | - | - | - | | `Transaction` | `ByteList[MAX_BYTES_PER_TRANSACTION]` | either a [typed transaction envelope](https://eips.ethereum.org/EIPS/eip-2718#opaque-byte-array-rather-than-an-rlp-array) or a legacy transaction| | `ExecutionAddress` | `Bytes20` | Address of account on the execution layer | ## Preset ### Execution | Name | Value | | - | - | | `MAX_BYTES_PER_TRANSACTION` | `uint64(2**30)` (= 1,073,741,824) | | `MAX_TRANSACTIONS_PER_PAYLOAD` | `uint64(2**20)` (= 1,048,576) | | `BYTES_PER_LOGS_BLOOM` | `uint64(2**8)` (= 256) | | `MAX_EXTRA_DATA_BYTES` | `2**5` (= 32) | ### Updated penalty values The Merge updates a few configuration values to move penalty parameters to their final, maximum security values. *Note*: The spec does *not* override previous configuration values but instead creates new values and replaces usage throughout. | Name | Value | | - | - | | `INACTIVITY_PENALTY_QUOTIENT_MERGE` | `uint64(2**24)` (= 16,777,216) | | `MIN_SLASHING_PENALTY_QUOTIENT_MERGE` | `uint64(2**5)` (= 32) | | `PROPORTIONAL_SLASHING_MULTIPLIER_MERGE` | `uint64(3)` | ## Configuration ### Transition settings | Name | Value | | - | - | | `TERMINAL_TOTAL_DIFFICULTY` | **TBD** | | `TERMINAL_BLOCK_HASH` | `Hash32()` | | `TERMINAL_BLOCK_HASH_ACTIVATION_EPOCH` | `FAR_FUTURE_EPOCH` | ## Containers ### Extended containers #### `BeaconBlockBody` ```python class BeaconBlockBody(Container): randao_reveal: BLSSignature eth1_data: Eth1Data # Eth1 data vote graffiti: Bytes32 # Arbitrary data # Operations proposer_slashings: List[ProposerSlashing, MAX_PROPOSER_SLASHINGS] attester_slashings: List[AttesterSlashing, MAX_ATTESTER_SLASHINGS] attestations: List[Attestation, MAX_ATTESTATIONS] deposits: List[Deposit, MAX_DEPOSITS] voluntary_exits: List[SignedVoluntaryExit, MAX_VOLUNTARY_EXITS] sync_aggregate: SyncAggregate # Execution execution_payload: ExecutionPayload # [New in Merge] ``` #### `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 # [New in Merge] ``` ### New containers #### `ExecutionPayload` ```python class ExecutionPayload(Container): # Execution block header fields parent_hash: Hash32 fee_recipient: ExecutionAddress # 'beneficiary' in the yellow paper state_root: Bytes32 receipt_root: Bytes32 # 'receipts root' in the yellow paper logs_bloom: ByteVector[BYTES_PER_LOGS_BLOOM] random: Bytes32 # 'difficulty' in the yellow paper block_number: uint64 # 'number' in the yellow paper 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 # Hash of execution block transactions: List[Transaction, MAX_TRANSACTIONS_PER_PAYLOAD] ``` #### `ExecutionPayloadHeader` ```python class ExecutionPayloadHeader(Container): # Execution block header fields parent_hash: Hash32 fee_recipient: ExecutionAddress state_root: Bytes32 receipt_root: Bytes32 logs_bloom: ByteVector[BYTES_PER_LOGS_BLOOM] random: 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 # Hash of execution block transactions_root: Root ``` ## Helper functions ### Predicates #### `is_merge_transition_complete` ```python def is_merge_transition_complete(state: BeaconState) -> bool: return state.latest_execution_payload_header != ExecutionPayloadHeader() ``` #### `is_merge_transition_block` ```python def is_merge_transition_block(state: BeaconState, body: BeaconBlockBody) -> bool: return not is_merge_transition_complete(state) and body.execution_payload != ExecutionPayload() ``` #### `is_execution_enabled` ```python def is_execution_enabled(state: BeaconState, body: BeaconBlockBody) -> bool: return is_merge_transition_block(state, body) or is_merge_transition_complete(state) ``` ### Misc #### `compute_timestamp_at_slot` *Note*: This function is unsafe with respect to overflows and underflows. ```python def compute_timestamp_at_slot(state: BeaconState, slot: Slot) -> uint64: slots_since_genesis = slot - GENESIS_SLOT return uint64(state.genesis_time + slots_since_genesis * SECONDS_PER_SLOT) ``` ### Beacon state accessors #### Modified `get_inactivity_penalty_deltas` *Note*: The function `get_inactivity_penalty_deltas` is modified to use `INACTIVITY_PENALTY_QUOTIENT_MERGE`. ```python def get_inactivity_penalty_deltas(state: BeaconState) -> Tuple[Sequence[Gwei], Sequence[Gwei]]: """ Return the inactivity penalty deltas by considering timely target participation flags and inactivity scores. """ rewards = [Gwei(0) for _ in range(len(state.validators))] penalties = [Gwei(0) for _ in range(len(state.validators))] previous_epoch = get_previous_epoch(state) matching_target_indices = get_unslashed_participating_indices(state, TIMELY_TARGET_FLAG_INDEX, previous_epoch) for index in get_eligible_validator_indices(state): if index not in matching_target_indices: penalty_numerator = state.validators[index].effective_balance * state.inactivity_scores[index] # [Modified in Merge] penalty_denominator = INACTIVITY_SCORE_BIAS * INACTIVITY_PENALTY_QUOTIENT_MERGE penalties[index] += Gwei(penalty_numerator // penalty_denominator) return rewards, penalties ``` ### Beacon state mutators #### Modified `slash_validator` *Note*: The function `slash_validator` is modified to use `MIN_SLASHING_PENALTY_QUOTIENT_MERGE`. ```python def slash_validator(state: BeaconState, slashed_index: ValidatorIndex, whistleblower_index: ValidatorIndex=None) -> None: """ Slash the validator with index ``slashed_index``. """ epoch = get_current_epoch(state) initiate_validator_exit(state, slashed_index) validator = state.validators[slashed_index] validator.slashed = True validator.withdrawable_epoch = max(validator.withdrawable_epoch, Epoch(epoch + EPOCHS_PER_SLASHINGS_VECTOR)) state.slashings[epoch % EPOCHS_PER_SLASHINGS_VECTOR] += validator.effective_balance slashing_penalty = validator.effective_balance // MIN_SLASHING_PENALTY_QUOTIENT_MERGE # [Modified in Merge] decrease_balance(state, slashed_index, slashing_penalty) # Apply proposer and whistleblower rewards proposer_index = get_beacon_proposer_index(state) if whistleblower_index is None: whistleblower_index = proposer_index whistleblower_reward = Gwei(validator.effective_balance // WHISTLEBLOWER_REWARD_QUOTIENT) proposer_reward = Gwei(whistleblower_reward * PROPOSER_WEIGHT // WEIGHT_DENOMINATOR) increase_balance(state, proposer_index, proposer_reward) increase_balance(state, whistleblower_index, Gwei(whistleblower_reward - proposer_reward)) ``` ## Beacon chain state transition function ### Execution engine The implementation-dependent `ExecutionEngine` protocol encapsulates the execution sub-system logic via: * a state object `self.execution_state` of type `ExecutionState` * a state transition function `self.execute_payload` which applies changes to the `self.execution_state` *Note*: `execute_payload` is a function accessed through the `EXECUTION_ENGINE` module which instantiates the `ExecutionEngine` protocol. The body of this function is implementation dependent. The Engine API may be used to implement this and similarly defined functions via an external execution engine. #### `execute_payload` ```python def execute_payload(self: ExecutionEngine, execution_payload: ExecutionPayload) -> bool: """ Return ``True`` if and only if ``execution_payload`` is valid with respect to ``self.execution_state``. """ ... ``` ### Block processing *Note*: The call to the `process_execution_payload` must happen before the call to the `process_randao` as the former depends on the `randao_mix` computed with the reveal of the previous block. ```python def process_block(state: BeaconState, block: BeaconBlock) -> None: process_block_header(state, block) if is_execution_enabled(state, block.body): process_execution_payload(state, block.body.execution_payload, EXECUTION_ENGINE) # [New in Merge] process_randao(state, block.body) process_eth1_data(state, block.body) process_operations(state, block.body) process_sync_aggregate(state, block.body.sync_aggregate) ``` #### Execution payload ##### `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 random assert payload.random == 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.execute_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, receipt_root=payload.receipt_root, logs_bloom=payload.logs_bloom, random=payload.random, 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), ) ``` ### Epoch processing #### Slashings *Note*: The function `process_slashings` is modified to use `PROPORTIONAL_SLASHING_MULTIPLIER_MERGE`. ```python def process_slashings(state: BeaconState) -> None: epoch = get_current_epoch(state) total_balance = get_total_active_balance(state) adjusted_total_slashing_balance = min( sum(state.slashings) * PROPORTIONAL_SLASHING_MULTIPLIER_MERGE, # [Modified in Merge] total_balance ) for index, validator in enumerate(state.validators): if validator.slashed and epoch + EPOCHS_PER_SLASHINGS_VECTOR // 2 == validator.withdrawable_epoch: increment = EFFECTIVE_BALANCE_INCREMENT # Factored out from penalty numerator to avoid uint64 overflow penalty_numerator = validator.effective_balance // increment * adjusted_total_slashing_balance penalty = penalty_numerator // total_balance * increment decrease_balance(state, ValidatorIndex(index), penalty) ``` ## Testing *Note*: The function `initialize_beacon_state_from_eth1` is modified for pure Merge testing only. Modifications include: 1. Use `MERGE_FORK_VERSION` as the current fork version. 2. Utilize the Merge `BeaconBlockBody` when constructing the initial `latest_block_header`. 3. Initialize `latest_execution_payload_header`. If `execution_payload_header == ExecutionPayloadHeader()`, then the Merge has not yet occurred. Else, the Merge starts from genesis and the transition is incomplete. ```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=MERGE_FORK_VERSION, # [Modified in Merge] for testing only current_version=MERGE_FORK_VERSION, # [Modified in Merge] 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) # [New in Merge] Initialize the execution payload header # If empty, will initialize a chain that has not yet gone through the Merge transition state.latest_execution_payload_header = execution_payload_header return state ```