38 KiB
38 KiB
Ethereum 2.0 Phase 1 -- The Beacon Chain for Shards
Notice: This document is a work-in-progress for researchers and implementers.
Table of contents
Table of Contents
- Introduction
- Custom types
- Configuration
- Updated containers
- New containers
- Helper functions
Introduction
This document describes the extensions made to the Phase 0 design of The Beacon Chain to facilitate the new shards as part of Phase 1 of Eth2.
Custom types
We define the following Python custom types for type hinting and readability:
| Name | SSZ equivalent | Description |
|---|---|---|
Shard |
uint64 |
a shard number |
OnlineEpochs |
uint8 |
online countdown epochs |
Configuration
Configuration is not namespaced. Instead it is strictly an extension; no constants of phase 0 change, but new constants are adopted for changing behaviors.
Misc
| Name | Value | Unit | Duration |
|---|---|---|---|
MAX_SHARDS |
2**10 (= 1024) |
||
ONLINE_PERIOD |
OnlineEpochs(2**3) (= 8) |
online epochs | ~51 min |
LIGHT_CLIENT_COMMITTEE_SIZE |
2**7 (= 128) |
||
LIGHT_CLIENT_COMMITTEE_PERIOD |
Epoch(2**8) (= 256) |
epochs | ~27 hours |
MAX_SHARD_BLOCK_SIZE |
2**20 (= 1,048,576) |
||
TARGET_SHARD_BLOCK_SIZE |
2**18 (= 262,144) |
||
SHARD_BLOCK_OFFSETS |
[1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233] |
||
MAX_SHARD_BLOCKS_PER_ATTESTATION |
len(SHARD_BLOCK_OFFSETS) |
||
MAX_GASPRICE |
Gwei(2**14) (= 16,384) |
Gwei | |
MIN_GASPRICE |
Gwei(2**3) (= 8) |
Gwei | |
GASPRICE_ADJUSTMENT_COEFFICIENT |
2**3 (= 8) |
||
DOMAIN_SHARD_PROPOSAL |
DomainType('0x80000000') |
||
DOMAIN_SHARD_COMMITTEE |
DomainType('0x81000000') |
||
DOMAIN_LIGHT_CLIENT |
DomainType('0x82000000') |
||
NO_SIGNATURE |
BLSSignature(b'\x00' * 96) |
Updated containers
The following containers have updated definitions in Phase 1.
Extended AttestationData
class AttestationData(Container):
slot: Slot
index: CommitteeIndex
# LMD GHOST vote
beacon_block_root: Root
# FFG vote
source: Checkpoint
target: Checkpoint
# Current-slot shard block root
head_shard_root: Root
# Shard transition root
shard_transition_root: Root
Extended Attestation
class Attestation(Container):
aggregation_bits: Bitlist[MAX_VALIDATORS_PER_COMMITTEE]
data: AttestationData
custody_bits_blocks: List[Bitlist[MAX_VALIDATORS_PER_COMMITTEE], MAX_SHARD_BLOCKS_PER_ATTESTATION]
signature: BLSSignature
Extended PendingAttestation
class PendingAttestation(Container):
aggregation_bits: Bitlist[MAX_VALIDATORS_PER_COMMITTEE]
data: AttestationData
inclusion_delay: Slot
proposer_index: ValidatorIndex
crosslink_success: boolean
Extended IndexedAttestation
class IndexedAttestation(Container):
committee: List[ValidatorIndex, MAX_VALIDATORS_PER_COMMITTEE]
attestation: Attestation
Extended AttesterSlashing
Note that the attestation_1 and attestation_2 have a new IndexedAttestation definition.
class AttesterSlashing(Container):
attestation_1: IndexedAttestation
attestation_2: IndexedAttestation
Extended Validator
class Validator(Container):
pubkey: BLSPubkey
withdrawal_credentials: Bytes32 # Commitment to pubkey for withdrawals
effective_balance: Gwei # Balance at stake
slashed: boolean
# Status epochs
activation_eligibility_epoch: Epoch # When criteria for activation were met
activation_epoch: Epoch
exit_epoch: Epoch
withdrawable_epoch: Epoch # When validator can withdraw funds
# Custody game
# next_custody_secret_to_reveal is initialised to the custody period
# (of the particular validator) in which the validator is activated
# = get_custody_period_for_validator(...)
next_custody_secret_to_reveal: uint64
max_reveal_lateness: Epoch
Extended BeaconBlockBody
class BeaconBlockBody(Container):
randao_reveal: BLSSignature
eth1_data: Eth1Data # Eth1 data vote
graffiti: Bytes32 # Arbitrary data
# Slashings
proposer_slashings: List[ProposerSlashing, MAX_PROPOSER_SLASHINGS]
attester_slashings: List[AttesterSlashing, MAX_ATTESTER_SLASHINGS]
# Attesting
attestations: List[Attestation, MAX_ATTESTATIONS]
# Entry & exit
deposits: List[Deposit, MAX_DEPOSITS]
voluntary_exits: List[SignedVoluntaryExit, MAX_VOLUNTARY_EXITS]
# Custody game
custody_slashings: List[SignedCustodySlashing, MAX_CUSTODY_SLASHINGS]
custody_key_reveals: List[CustodyKeyReveal, MAX_CUSTODY_KEY_REVEALS]
early_derived_secret_reveals: List[EarlyDerivedSecretReveal, MAX_EARLY_DERIVED_SECRET_REVEALS]
# Shards
shard_transitions: Vector[ShardTransition, MAX_SHARDS]
# Light clients
light_client_signature_bitfield: Bitvector[LIGHT_CLIENT_COMMITTEE_SIZE]
light_client_signature: BLSSignature
Extended BeaconBlock
Note that the body has a new BeaconBlockBody definition.
class BeaconBlock(Container):
slot: Slot
proposer_index: ValidatorIndex
parent_root: Root
state_root: Root
body: BeaconBlockBody
Extended SignedBeaconBlock
Note that the message has a new BeaconBlock definition.
class SignedBeaconBlock(Container):
message: BeaconBlock
signature: BLSSignature
Extended BeaconState
Note that aside from the new additions, Validator and PendingAttestation have new definitions.
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[Root, EPOCHS_PER_HISTORICAL_VECTOR]
# Slashings
slashings: Vector[Gwei, EPOCHS_PER_SLASHINGS_VECTOR] # Per-epoch sums of slashed effective balances
# Attestations
previous_epoch_attestations: List[PendingAttestation, MAX_ATTESTATIONS * SLOTS_PER_EPOCH]
current_epoch_attestations: List[PendingAttestation, MAX_ATTESTATIONS * SLOTS_PER_EPOCH]
# Finality
justification_bits: Bitvector[JUSTIFICATION_BITS_LENGTH] # Bit set for every recent justified epoch
previous_justified_checkpoint: Checkpoint # Previous epoch snapshot
current_justified_checkpoint: Checkpoint
finalized_checkpoint: Checkpoint
# Phase 1
shard_states: List[ShardState, MAX_SHARDS]
online_countdown: List[OnlineEpochs, VALIDATOR_REGISTRY_LIMIT] # not a raw byte array, considered its large size.
current_light_committee: CompactCommittee
next_light_committee: CompactCommittee
# Custody game
# Future derived secrets already exposed; contains the indices of the exposed validator
# at RANDAO reveal period % EARLY_DERIVED_SECRET_PENALTY_MAX_FUTURE_EPOCHS
exposed_derived_secrets: Vector[List[ValidatorIndex, MAX_EARLY_DERIVED_SECRET_REVEALS * SLOTS_PER_EPOCH],
EARLY_DERIVED_SECRET_PENALTY_MAX_FUTURE_EPOCHS]
New containers
The following containers are new in Phase 1.
ShardBlock
class ShardBlock(Container):
shard_parent_root: Root
beacon_parent_root: Root
slot: Slot
proposer_index: ValidatorIndex
body: ByteList[MAX_SHARD_BLOCK_SIZE]
SignedShardBlock
class SignedShardBlock(Container):
message: ShardBlock
signature: BLSSignature
ShardBlockHeader
class ShardBlockHeader(Container):
shard_parent_root: Root
beacon_parent_root: Root
slot: Slot
proposer_index: ValidatorIndex
body_root: Root
ShardState
class ShardState(Container):
slot: Slot
gasprice: Gwei
transition_digest: Bytes32
latest_block_root: Root
ShardTransition
class ShardTransition(Container):
# Starting from slot
start_slot: Slot
# Shard block lengths
shard_block_lengths: List[uint64, MAX_SHARD_BLOCKS_PER_ATTESTATION]
# Shard data roots
shard_data_roots: List[Bytes32, MAX_SHARD_BLOCKS_PER_ATTESTATION]
# Intermediate shard states
shard_states: List[ShardState, MAX_SHARD_BLOCKS_PER_ATTESTATION]
# Proposer signature aggregate
proposer_signature_aggregate: BLSSignature
CompactCommittee
class CompactCommittee(Container):
pubkeys: List[BLSPubkey, MAX_VALIDATORS_PER_COMMITTEE]
compact_validators: List[uint64, MAX_VALIDATORS_PER_COMMITTEE]
AttestationCustodyBitWrapper
class AttestationCustodyBitWrapper(Container):
attestation_data_root: Root
block_index: uint64
bit: boolean
Helper functions
Misc
compute_previous_slot
def compute_previous_slot(slot: Slot) -> Slot:
if slot > 0:
return Slot(slot - 1)
else:
return Slot(0)
pack_compact_validator
def pack_compact_validator(index: ValidatorIndex, slashed: bool, balance_in_increments: uint64) -> uint64:
"""
Create a compact validator object representing index, slashed status, and compressed balance.
Takes as input balance-in-increments (// EFFECTIVE_BALANCE_INCREMENT) to preserve symmetry with
the unpacking function.
"""
return (index << 16) + (slashed << 15) + balance_in_increments
unpack_compact_validator
def unpack_compact_validator(compact_validator: uint64) -> Tuple[ValidatorIndex, bool, uint64]:
"""
Return validator index, slashed, balance // EFFECTIVE_BALANCE_INCREMENT
"""
return (
ValidatorIndex(compact_validator >> 16),
bool((compact_validator >> 15) % 2),
compact_validator & (2**15 - 1),
)
committee_to_compact_committee
def committee_to_compact_committee(state: BeaconState, committee: Sequence[ValidatorIndex]) -> CompactCommittee:
"""
Given a state and a list of validator indices, outputs the CompactCommittee representing them.
"""
validators = [state.validators[i] for i in committee]
compact_validators = [
pack_compact_validator(i, v.slashed, v.effective_balance // EFFECTIVE_BALANCE_INCREMENT)
for i, v in zip(committee, validators)
]
pubkeys = [v.pubkey for v in validators]
return CompactCommittee(pubkeys=pubkeys, compact_validators=compact_validators)
compute_shard_from_committee_index
def compute_shard_from_committee_index(state: BeaconState, index: CommitteeIndex, slot: Slot) -> Shard:
active_shards = get_active_shard_count(state)
return Shard((index + get_start_shard(state, slot)) % active_shards)
compute_offset_slots
def compute_offset_slots(start_slot: Slot, end_slot: Slot) -> Sequence[Slot]:
"""
Return the offset slots that are greater than ``start_slot`` and less than ``end_slot``.
"""
return [Slot(start_slot + x) for x in SHARD_BLOCK_OFFSETS if start_slot + x < end_slot]
compute_updated_gasprice
def compute_updated_gasprice(prev_gasprice: Gwei, length: uint8) -> Gwei:
if length > TARGET_SHARD_BLOCK_SIZE:
delta = (prev_gasprice * (length - TARGET_SHARD_BLOCK_SIZE)
// TARGET_SHARD_BLOCK_SIZE // GASPRICE_ADJUSTMENT_COEFFICIENT)
return min(prev_gasprice + delta, MAX_GASPRICE)
else:
delta = (prev_gasprice * (TARGET_SHARD_BLOCK_SIZE - length)
// TARGET_SHARD_BLOCK_SIZE // GASPRICE_ADJUSTMENT_COEFFICIENT)
return max(prev_gasprice, MIN_GASPRICE + delta) - delta
Beacon state accessors
get_active_shard_count
def get_active_shard_count(state: BeaconState) -> uint64:
return len(state.shard_states) # May adapt in the future, or change over time.
get_online_validator_indices
def get_online_validator_indices(state: BeaconState) -> Set[ValidatorIndex]:
active_validators = get_active_validator_indices(state, get_current_epoch(state))
return set([i for i in active_validators if state.online_countdown[i] != 0])
get_shard_committee
def get_shard_committee(beacon_state: BeaconState, epoch: Epoch, shard: Shard) -> Sequence[ValidatorIndex]:
source_epoch = epoch - epoch % SHARD_COMMITTEE_PERIOD
if source_epoch >= SHARD_COMMITTEE_PERIOD:
source_epoch -= SHARD_COMMITTEE_PERIOD
active_validator_indices = get_active_validator_indices(beacon_state, source_epoch)
seed = get_seed(beacon_state, source_epoch, DOMAIN_SHARD_COMMITTEE)
active_shard_count = get_active_shard_count(beacon_state)
return compute_committee(
indices=active_validator_indices,
seed=seed,
index=shard,
count=active_shard_count,
)
get_light_client_committee
def get_light_client_committee(beacon_state: BeaconState, epoch: Epoch) -> Sequence[ValidatorIndex]:
source_epoch = epoch - epoch % LIGHT_CLIENT_COMMITTEE_PERIOD
if source_epoch >= LIGHT_CLIENT_COMMITTEE_PERIOD:
source_epoch -= LIGHT_CLIENT_COMMITTEE_PERIOD
active_validator_indices = get_active_validator_indices(beacon_state, source_epoch)
seed = get_seed(beacon_state, source_epoch, DOMAIN_LIGHT_CLIENT)
return compute_committee(
indices=active_validator_indices,
seed=seed,
index=0,
count=get_active_shard_count(beacon_state),
)[:TARGET_COMMITTEE_SIZE]
get_shard_proposer_index
def get_shard_proposer_index(beacon_state: BeaconState, slot: Slot, shard: Shard) -> ValidatorIndex:
committee = get_shard_committee(beacon_state, compute_epoch_at_slot(slot), shard)
r = bytes_to_int(get_seed(beacon_state, get_current_epoch(beacon_state), DOMAIN_SHARD_COMMITTEE)[:8])
return committee[r % len(committee)]
get_indexed_attestation
def get_indexed_attestation(beacon_state: BeaconState, attestation: Attestation) -> IndexedAttestation:
committee = get_beacon_committee(beacon_state, attestation.data.slot, attestation.data.index)
return IndexedAttestation(
committee=committee,
attestation=attestation,
)
get_start_shard
def get_start_shard(state: BeaconState, slot: Slot) -> Shard:
# TODO: implement start shard logic
return Shard(0)
get_shard
def get_shard(state: BeaconState, attestation: Attestation) -> Shard:
return compute_shard_from_committee_index(state, attestation.data.index, attestation.data.slot)
get_latest_slot_for_shard
def get_latest_slot_for_shard(state: BeaconState, shard: Shard) -> Slot:
return state.shard_states[shard].slot
get_offset_slots
def get_offset_slots(state: BeaconState, shard: Shard) -> Sequence[Slot]:
return compute_offset_slots(state.shard_states[shard].slot, state.slot)
Predicates
Updated is_valid_indexed_attestation
Note that this replaces the Phase 0 is_valid_indexed_attestation.
def is_valid_indexed_attestation(state: BeaconState, indexed_attestation: IndexedAttestation) -> bool:
"""
Check if ``indexed_attestation`` has valid indices and signature.
"""
# Verify aggregate signature
all_pubkeys = []
all_signing_roots = []
attestation = indexed_attestation.attestation
domain = get_domain(state, DOMAIN_BEACON_ATTESTER, attestation.data.target.epoch)
aggregation_bits = attestation.aggregation_bits
if not any(aggregation_bits) or len(aggregation_bits) != len(indexed_attestation.committee):
return False
if len(attestation.custody_bits_blocks) == 0:
# fall back on phase0 behavior if there is no shard data.
for participant, abit in zip(indexed_attestation.committee, aggregation_bits):
if abit:
all_pubkeys.append(state.validators[participant].pubkey)
signing_root = compute_signing_root(indexed_attestation.attestation.data, domain)
return bls.FastAggregateVerify(all_pubkeys, signing_root, signature=attestation.signature)
else:
for i, custody_bits in enumerate(attestation.custody_bits_blocks):
assert len(custody_bits) == len(indexed_attestation.committee)
for participant, abit, cbit in zip(indexed_attestation.committee, aggregation_bits, custody_bits):
if abit:
all_pubkeys.append(state.validators[participant].pubkey)
# Note: only 2N distinct message hashes
attestation_wrapper = AttestationCustodyBitWrapper(
attestation_data_root=hash_tree_root(attestation.data),
block_index=i,
bit=cbit
)
all_signing_roots.append(compute_signing_root(attestation_wrapper, domain))
else:
assert not cbit
return bls.AggregateVerify(all_pubkeys, all_signing_roots, signature=attestation.signature)
is_shard_attestation
def is_shard_attestation(state: BeaconState,
attestation: Attestation,
committee_index: CommitteeIndex) -> bool:
if not (
attestation.data.index == committee_index
and attestation.data.slot + MIN_ATTESTATION_INCLUSION_DELAY == state.slot # Must be on-time attestation
# TODO: MIN_ATTESTATION_INCLUSION_DELAY should always be 1
):
return False
return True
is_winning_attestation
def is_winning_attestation(state: BeaconState,
attestation: PendingAttestation,
committee_index: CommitteeIndex,
winning_root: Root) -> bool:
"""
Check if ``attestation`` helped contribute to the successful crosslink of
``winning_root`` formed by ``committee_index`` committee at the current slot.
"""
return (
attestation.data.slot == state.slot
and attestation.data.index == committee_index
and attestation.data.shard_transition_root == winning_root
)
optional_aggregate_verify
def optional_aggregate_verify(pubkeys: Sequence[BLSPubkey],
messages: Sequence[Bytes32],
signature: BLSSignature) -> bool:
"""
If ``pubkeys`` is an empty list, the given ``signature`` should be a stub ``NO_SIGNATURE``.
Otherwise, verify it with standard BLS AggregateVerify API.
"""
if len(pubkeys) == 0:
return signature == NO_SIGNATURE
else:
return bls.AggregateVerify(pubkeys, messages, signature)
optional_fast_aggregate_verify
def optional_fast_aggregate_verify(pubkeys: Sequence[BLSPubkey], message: Bytes32, signature: BLSSignature) -> bool:
"""
If ``pubkeys`` is an empty list, the given ``signature`` should be a stub ``NO_SIGNATURE``.
Otherwise, verify it with standard BLS FastAggregateVerify API.
"""
if len(pubkeys) == 0:
return signature == NO_SIGNATURE
else:
return bls.FastAggregateVerify(pubkeys, message, signature)
Block processing
def process_block(state: BeaconState, block: BeaconBlock) -> None:
process_block_header(state, block)
process_randao(state, block.body)
process_eth1_data(state, block.body)
process_light_client_signatures(state, block.body)
process_operations(state, block.body)
verify_shard_transition_false_positives(state, block.body)
Operations
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)
# New attestation processing
for_ops(body.attestations, process_attestation)
for_ops(body.deposits, process_deposit)
for_ops(body.voluntary_exits, process_voluntary_exit)
# See custody game spec.
process_custody_game_operations(state, body)
process_crosslinks(state, body.shard_transitions, body.attestations)
# TODO process_operations(body.shard_receipt_proofs, process_shard_receipt_proofs)
New Attestation processing
validate_attestation
def validate_attestation(state: BeaconState, attestation: Attestation) -> None:
data = attestation.data
assert data.index < get_committee_count_at_slot(state, data.slot)
assert data.index < get_active_shard_count(state)
assert data.target.epoch in (get_previous_epoch(state), get_current_epoch(state))
assert data.target.epoch == compute_epoch_at_slot(data.slot)
assert data.slot + MIN_ATTESTATION_INCLUSION_DELAY <= state.slot <= data.slot + SLOTS_PER_EPOCH
committee = get_beacon_committee(state, data.slot, data.index)
assert len(attestation.aggregation_bits) == len(committee)
if attestation.data.target.epoch == get_current_epoch(state):
assert attestation.data.source == state.current_justified_checkpoint
else:
assert attestation.data.source == state.previous_justified_checkpoint
shard = get_shard(state, attestation)
# Type 1: on-time attestations, the custody bits should be non-empty.
if attestation.custody_bits_blocks != []:
# Ensure on-time attestation
assert data.slot + MIN_ATTESTATION_INCLUSION_DELAY == state.slot
# Correct data root count
assert len(attestation.custody_bits_blocks) == len(get_offset_slots(state, shard))
# Correct parent block root
assert data.beacon_block_root == get_block_root_at_slot(state, compute_previous_slot(state.slot))
# Type 2: no shard transition, no custody bits
else:
# Ensure delayed attestation
assert data.slot + MIN_ATTESTATION_INCLUSION_DELAY < state.slot
# Late attestations cannot have a shard transition root
assert data.shard_transition_root == Root()
# Signature check
assert is_valid_indexed_attestation(state, get_indexed_attestation(state, attestation))
apply_shard_transition
def apply_shard_transition(state: BeaconState, shard: Shard, transition: ShardTransition) -> None:
# TODO: only need to check it once when phase 1 starts
assert state.slot > PHASE_1_GENESIS_SLOT
# Correct data root count
offset_slots = get_offset_slots(state, shard)
assert (
len(transition.shard_data_roots)
== len(transition.shard_states)
== len(transition.shard_block_lengths)
== len(offset_slots)
)
assert transition.start_slot == offset_slots[0]
headers = []
proposers = []
prev_gasprice = state.shard_states[shard].gasprice
shard_parent_root = state.shard_states[shard].latest_block_root
for i in range(len(offset_slots)):
shard_block_length = transition.shard_block_lengths[i]
shard_state = transition.shard_states[i]
# Verify correct calculation of gas prices and slots
assert shard_state.gasprice == compute_updated_gasprice(prev_gasprice, shard_block_length)
assert shard_state.slot == offset_slots[i]
# Collect the non-empty proposals result
is_empty_proposal = shard_block_length == 0
if not is_empty_proposal:
proposal_index = get_shard_proposer_index(state, offset_slots[i], shard)
# Reconstruct shard headers
header = ShardBlockHeader(
shard_parent_root=shard_parent_root,
beacon_parent_root=get_block_root_at_slot(state, offset_slots[i]),
proposer_index=proposal_index,
slot=offset_slots[i],
body_root=transition.shard_data_roots[i]
)
shard_parent_root = hash_tree_root(header)
headers.append(header)
proposers.append(proposal_index)
prev_gasprice = shard_state.gasprice
pubkeys = [state.validators[proposer].pubkey for proposer in proposers]
signing_roots = [
compute_signing_root(header, get_domain(state, DOMAIN_SHARD_PROPOSAL, compute_epoch_at_slot(header.slot)))
for header in headers
]
# Verify combined proposer signature
assert optional_aggregate_verify(pubkeys, signing_roots, transition.proposer_signature_aggregate)
# Save updated state
state.shard_states[shard] = transition.shard_states[len(transition.shard_states) - 1]
state.shard_states[shard].slot = state.slot - 1
process_crosslink_for_shard
def process_crosslink_for_shard(state: BeaconState,
committee_index: CommitteeIndex,
shard_transition: ShardTransition,
attestations: Sequence[Attestation]) -> Root:
committee = get_beacon_committee(state, state.slot, committee_index)
online_indices = get_online_validator_indices(state)
shard = compute_shard_from_committee_index(state, committee_index, state.slot)
# Loop over all shard transition roots
shard_transition_roots = set([a.data.shard_transition_root for a in attestations])
for shard_transition_root in sorted(shard_transition_roots):
transition_attestations = [a for a in attestations if a.data.shard_transition_root == shard_transition_root]
transition_participants: Set[ValidatorIndex] = set()
for attestation in transition_attestations:
participants = get_attesting_indices(state, attestation.data, attestation.aggregation_bits)
transition_participants = transition_participants.union(participants)
assert attestation.data.head_shard_root == shard_transition.shard_data_roots[
len(shard_transition.shard_data_roots) - 1
]
enough_online_stake = (
get_total_balance(state, online_indices.intersection(transition_participants)) * 3 >=
get_total_balance(state, online_indices.intersection(committee)) * 2
)
# If not enough stake, try next transition root
if not enough_online_stake:
continue
# Attestation <-> shard transition consistency
assert shard_transition_root == hash_tree_root(shard_transition)
# Apply transition
apply_shard_transition(state, shard, shard_transition)
# Apply proposer reward and cost
beacon_proposer_index = get_beacon_proposer_index(state)
estimated_attester_reward = sum([get_base_reward(state, attester) for attester in transition_participants])
proposer_reward = Gwei(estimated_attester_reward // PROPOSER_REWARD_QUOTIENT)
increase_balance(state, beacon_proposer_index, proposer_reward)
states_slots_lengths = zip(
shard_transition.shard_states,
get_offset_slots(state, shard),
shard_transition.shard_block_lengths
)
for shard_state, slot, length in states_slots_lengths:
proposer_index = get_shard_proposer_index(state, slot, shard)
decrease_balance(state, proposer_index, shard_state.gasprice * length)
# Return winning transition root
return shard_transition_root
# No winning transition root, ensure empty and return empty root
assert shard_transition == ShardTransition()
return Root()
process_crosslinks
def process_crosslinks(state: BeaconState,
shard_transitions: Sequence[ShardTransition],
attestations: Sequence[Attestation]) -> None:
committee_count = get_committee_count_at_slot(state, state.slot)
for committee_index in map(CommitteeIndex, range(committee_count)):
shard = compute_shard_from_committee_index(state, committee_index, state.slot)
# All attestations in the block for this committee/shard and current slot
shard_transition = shard_transitions[shard]
shard_attestations = [
attestation for attestation in attestations
if is_shard_attestation(state, attestation, committee_index)
]
winning_root = process_crosslink_for_shard(state, committee_index, shard_transition, shard_attestations)
if winning_root != Root():
# Mark relevant pending attestations as creating a successful crosslink
for pending_attestation in state.current_epoch_attestations:
if is_winning_attestation(state, pending_attestation, committee_index, winning_root):
pending_attestation.crosslink_success = True
process_attestation
def process_attestation(state: BeaconState, attestation: Attestation) -> None:
validate_attestation(state, attestation)
# Store pending attestation for epoch processing
pending_attestation = PendingAttestation(
aggregation_bits=attestation.aggregation_bits,
data=attestation.data,
inclusion_delay=state.slot - attestation.data.slot,
proposer_index=get_beacon_proposer_index(state),
crosslink_success=False, # To be filled in during process_crosslinks
)
if attestation.data.target.epoch == get_current_epoch(state):
state.current_epoch_attestations.append(pending_attestation)
else:
state.previous_epoch_attestations.append(pending_attestation)
New Attester slashing processing
def get_indices_from_committee(
committee: List[ValidatorIndex, MAX_VALIDATORS_PER_COMMITTEE],
bits: Bitlist[MAX_VALIDATORS_PER_COMMITTEE]) -> List[ValidatorIndex, MAX_VALIDATORS_PER_COMMITTEE]:
assert len(bits) == len(committee)
return List[ValidatorIndex, MAX_VALIDATORS_PER_COMMITTEE](
[validator_index for i, validator_index in enumerate(committee) if bits[i]]
)
def process_attester_slashing(state: BeaconState, attester_slashing: AttesterSlashing) -> None:
indexed_attestation_1 = attester_slashing.attestation_1
indexed_attestation_2 = attester_slashing.attestation_2
assert is_slashable_attestation_data(
indexed_attestation_1.attestation.data,
indexed_attestation_2.attestation.data,
)
assert is_valid_indexed_attestation(state, indexed_attestation_1)
assert is_valid_indexed_attestation(state, indexed_attestation_2)
indices_1 = get_indices_from_committee(
indexed_attestation_1.committee,
indexed_attestation_1.attestation.aggregation_bits,
)
indices_2 = get_indices_from_committee(
indexed_attestation_2.committee,
indexed_attestation_2.attestation.aggregation_bits,
)
slashed_any = False
indices = set(indices_1).intersection(indices_2)
for index in sorted(indices):
if is_slashable_validator(state.validators[index], get_current_epoch(state)):
slash_validator(state, index)
slashed_any = True
assert slashed_any
Shard transition false positives
def verify_shard_transition_false_positives(state: BeaconState, block_body: BeaconBlockBody) -> None:
# Verify that a `shard_transition` in a block is empty if an attestation was not processed for it
for shard in range(get_active_shard_count(state)):
if state.shard_states[shard].slot != state.slot - 1:
assert block_body.shard_transitions[shard] == ShardTransition()
Light client processing
def process_light_client_signatures(state: BeaconState, block_body: BeaconBlockBody) -> None:
committee = get_light_client_committee(state, get_current_epoch(state))
total_reward = Gwei(0)
signer_pubkeys = []
for bit_index, participant_index in enumerate(committee):
if block_body.light_client_signature_bitfield[bit_index]:
signer_pubkeys.append(state.validators[participant_index].pubkey)
increase_balance(state, participant_index, get_base_reward(state, participant_index))
total_reward += get_base_reward(state, participant_index)
increase_balance(state, get_beacon_proposer_index(state), Gwei(total_reward // PROPOSER_REWARD_QUOTIENT))
slot = compute_previous_slot(state.slot)
signing_root = compute_signing_root(get_block_root_at_slot(state, slot),
get_domain(state, DOMAIN_LIGHT_CLIENT, compute_epoch_at_slot(slot)))
assert optional_fast_aggregate_verify(signer_pubkeys, signing_root, block_body.light_client_signature)
Epoch transition
This epoch transition overrides the phase0 epoch transition:
def process_epoch(state: BeaconState) -> None:
process_justification_and_finalization(state)
process_rewards_and_penalties(state)
process_registry_updates(state)
process_reveal_deadlines(state)
process_slashings(state)
process_final_updates(state)
process_custody_final_updates(state)
process_online_tracking(state)
process_light_client_committee_updates(state)
Custody game updates
process_reveal_deadlines and process_custody_final_updates are defined in the Custody Game spec,
Online-tracking
def process_online_tracking(state: BeaconState) -> None:
# Slowly remove validators from the "online" set if they do not show up
for index in range(len(state.validators)):
if state.online_countdown[index] != 0:
state.online_countdown[index] = state.online_countdown[index] - 1
# Process pending attestations
for pending_attestation in state.current_epoch_attestations + state.previous_epoch_attestations:
for index in get_attesting_indices(state, pending_attestation.data, pending_attestation.aggregation_bits):
state.online_countdown[index] = ONLINE_PERIOD
Light client committee updates
def process_light_client_committee_updates(state: BeaconState) -> None:
# Update light client committees
if get_current_epoch(state) % LIGHT_CLIENT_COMMITTEE_PERIOD == 0:
state.current_light_committee = state.next_light_committee
new_committee = get_light_client_committee(state, get_current_epoch(state) + LIGHT_CLIENT_COMMITTEE_PERIOD)
state.next_light_committee = committee_to_compact_committee(state, new_committee)