Remove work-in-progress notes in Bellatrix specs (#3033 )

* Remove the work-in-progress note in Bellatrix spec

Bellatrix is done and released.

* Remove work-in-progress notes in Bellatrix specs

* Remove work-in-progress notes in Bellatrix specs

* Remove work-in-progress notes in Bellatrix specs

2022-10-15 05:05:45 +08:00

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Bellatrix -- The Beacon Chain

Introduction
Custom types
Preset
- Execution
- Updated penalty values
Configuration
- Transition settings
Containers
- Extended containers
  - BeaconBlockBody
  - BeaconState
- New containers
  - ExecutionPayload
  - ExecutionPayloadHeader
Helper functions
Beacon chain state transition function
Testing

Introduction

This upgrade adds transaction execution to the beacon chain as part of Bellatrix upgrade.

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 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

Bellatrix 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_BELLATRIX`	`uint64(2**24)` (= 16,777,216)
`MIN_SLASHING_PENALTY_QUOTIENT_BELLATRIX`	`uint64(2**5)` (= 32)
`PROPORTIONAL_SLASHING_MULTIPLIER_BELLATRIX`	`uint64(3)`

Configuration

Transition settings

Name	Value
`TERMINAL_TOTAL_DIFFICULTY`	`58750000000000000000000` (Estimated: Sept 15, 2022)
`TERMINAL_BLOCK_HASH`	`Hash32()`
`TERMINAL_BLOCK_HASH_ACTIVATION_EPOCH`	`FAR_FUTURE_EPOCH`

Containers

Extended containers

`BeaconBlockBody`

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 Bellatrix]

`BeaconState`

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 Bellatrix]

New containers

`ExecutionPayload`

class ExecutionPayload(Container):
    # Execution block header fields
    parent_hash: Hash32
    fee_recipient: ExecutionAddress  # 'beneficiary' in the yellow paper
    state_root: Bytes32
    receipts_root: Bytes32
    logs_bloom: ByteVector[BYTES_PER_LOGS_BLOOM]
    prev_randao: 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`

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  # Hash of execution block
    transactions_root: Root

Helper functions

Predicates

`is_merge_transition_complete`

def is_merge_transition_complete(state: BeaconState) -> bool:
    return state.latest_execution_payload_header != ExecutionPayloadHeader()

`is_merge_transition_block`

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`

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.

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_BELLATRIX.

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 Bellatrix]
            penalty_denominator = INACTIVITY_SCORE_BIAS * INACTIVITY_PENALTY_QUOTIENT_BELLATRIX
            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_BELLATRIX.

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_BELLATRIX  # [Modified in Bellatrix]
    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 notification function self.notify_new_payload which may apply changes to the self.execution_state

Note: notify_new_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.

`notify_new_payload`

def notify_new_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.

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 Bellatrix]
    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`

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),
    )

Epoch processing

Slashings

Note: The function process_slashings is modified to use PROPORTIONAL_SLASHING_MULTIPLIER_BELLATRIX.

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_BELLATRIX,  # [Modified in Bellatrix]
        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 Bellatrix testing only. Modifications include:

Use BELLATRIX_FORK_VERSION as the previous and current fork version.
Utilize the Bellatrix BeaconBlockBody when constructing the initial latest_block_header.
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.

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=BELLATRIX_FORK_VERSION,  # [Modified in Bellatrix] for testing only
        current_version=BELLATRIX_FORK_VERSION,  # [Modified in Bellatrix]
        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 Bellatrix] 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

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