Bellatrix -- The Beacon Chain
Table of contents
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]
|
| 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
Request data
NewPayloadRequest
| @dataclass
class NewPayloadRequest(object):
execution_payload: ExecutionPayload
|
Engine APIs
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
The body of these functions are implementation dependent.
The Engine API may be used to implement this and similarly defined functions via an external execution engine.
notify_new_payload
notify_new_payload
is a function accessed through the EXECUTION_ENGINE
module which instantiates the ExecutionEngine
protocol.
| 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``.
"""
...
|
is_valid_block_hash
| def is_valid_block_hash(self: ExecutionEngine, execution_payload: ExecutionPayload) -> bool:
"""
Return ``True`` if and only if ``execution_payload.block_hash`` is computed correctly.
"""
...
|
verify_and_notify_new_payload
| def verify_and_notify_new_payload(self: ExecutionEngine,
new_payload_request: NewPayloadRequest) -> bool:
"""
Return ``True`` if and only if ``new_payload_request`` is valid with respect to ``self.execution_state``.
"""
execution_payload = new_payload_request.execution_payload
if b'' in execution_payload.transactions:
return False
if not self.is_valid_block_hash(execution_payload):
return False
if not self.notify_new_payload(execution_payload):
return False
return True
|
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_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, body: BeaconBlockBody, execution_engine: ExecutionEngine) -> None:
payload = body.execution_payload
# 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.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),
)
|
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:
1. Use BELLATRIX_FORK_VERSION
as the previous and current fork version.
2. Utilize the Bellatrix 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.
| 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
|