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Merge pull request #783 from ethereum/JustinDrake-patch-11 

Simplify and cleanup process_attestation
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Danny Ryan 2019-03-19 12:19:06 -06:00 committed by GitHub
parent f789450743 bdfc01cf93
commit 4111797550
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1 changed files with 33 additions and 58 deletions
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specs/core/0_beacon-chain.md
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@ -2362,74 +2362,49 @@ def process_attestation(state: BeaconState, attestation: Attestation) -> None:
Process ``Attestation`` transaction.
Note that this function mutates ``state``.
"""
# Can't submit attestations that are too far in history (or in prehistory)
assert attestation.data.slot >= GENESIS_SLOT
assert state.slot <= attestation.data.slot + SLOTS_PER_EPOCH
# Can't submit attestations too quickly
assert attestation.data.slot + MIN_ATTESTATION_INCLUSION_DELAY <= state.slot
# Verify that the justified epoch and root is correct
if slot_to_epoch(attestation.data.slot) >= get_current_epoch(state):
# Case 1: current epoch attestations
assert attestation.data.source_epoch == state.current_justified_epoch
assert attestation.data.source_root == state.current_justified_root
else:
# Case 2: previous epoch attestations
assert attestation.data.source_epoch == state.previous_justified_epoch
assert attestation.data.source_root == state.previous_justified_root
# Check that the crosslink data is valid
acceptable_crosslink_data = {
# Case 1: Latest crosslink matches the one in the state
attestation.data.previous_crosslink,
# Case 2: State has already been updated, state's latest crosslink matches the crosslink
# the attestation is trying to create
Crosslink(
crosslink_data_root=attestation.data.crosslink_data_root,
epoch=slot_to_epoch(attestation.data.slot)
)
}
assert state.latest_crosslinks[attestation.data.shard] in acceptable_crosslink_data
# Attestation must be nonempty!
assert attestation.aggregation_bitfield != b'\x00' * len(attestation.aggregation_bitfield)
# Custody must be empty (to be removed in phase 1)
assert attestation.custody_bitfield == b'\x00' * len(attestation.custody_bitfield)
# Get the committee for the specific shard that this attestation is for
crosslink_committee = [
committee for committee, shard in get_crosslink_committees_at_slot(state, attestation.data.slot)
if shard == attestation.data.shard
][0]
# Custody bitfield must be a subset of the attestation bitfield
for i in range(len(crosslink_committee)):
if get_bitfield_bit(attestation.aggregation_bitfield, i) == 0b0:
assert get_bitfield_bit(attestation.custody_bitfield, i) == 0b0
# Verify aggregate signature
participants = get_attestation_participants(state, attestation.data, attestation.aggregation_bitfield)
custody_bit_1_participants = get_attestation_participants(state, attestation.data, attestation.custody_bitfield)
custody_bit_0_participants = [i for i in participants if i not in custody_bit_1_participants]
assert max(GENESIS_SLOT, state.slot - SLOTS_PER_EPOCH) <= attestation.data.slot
assert attestation.data.slot <= state.slot - MIN_ATTESTATION_INCLUSION_DELAY
assert bls_verify_multiple(
pubkeys=[
bls_aggregate_pubkeys([state.validator_registry[i].pubkey for i in custody_bit_0_participants]),
bls_aggregate_pubkeys([state.validator_registry[i].pubkey for i in custody_bit_1_participants]),
],
message_hashes=[
hash_tree_root(AttestationDataAndCustodyBit(data=attestation.data, custody_bit=0b0)),
hash_tree_root(AttestationDataAndCustodyBit(data=attestation.data, custody_bit=0b1)),
],
# Check target epoch, source epoch, and source root
target_epoch = slot_to_epoch(attestation.data.slot)
assert (target_epoch, attestation.data.source_epoch, attestation.data.source_root) in {
(get_current_epoch(state), state.current_justified_epoch, state.current_justified_root),
(get_previous_epoch(state), state.previous_justified_epoch, state.previous_justified_root),
}
# Check crosslink data
assert attestation.data.crosslink_data_root == ZERO_HASH # [to be removed in phase 1]
assert state.latest_crosslinks[attestation.data.shard] in {
attestation.data.previous_crosslink, # Case 1: latest crosslink matches previous crosslink
Crosslink( # Case 2: latest crosslink matches current crosslink
crosslink_data_root=attestation.data.crosslink_data_root,
epoch=target_epoch,
),
}
# Check custody bits [to be generalised in phase 1]
assert attestation.custody_bitfield == b'\x00' * len(attestation.custody_bitfield)
# Check aggregate signature [to be generalised in phase 1]
participants = get_attestation_participants(state, attestation.data, attestation.aggregation_bitfield)
assert len(participants) != 0
assert bls_verify(
pubkey=bls_aggregate_pubkeys([state.validator_registry[i].pubkey for i in participants]),
message_hash=hash_tree_root(AttestationDataAndCustodyBit(data=attestation.data, custody_bit=0b0)),
signature=attestation.aggregate_signature,
domain=get_domain(state.fork, slot_to_epoch(attestation.data.slot), DOMAIN_ATTESTATION),
domain=get_domain(state.fork, target_epoch, DOMAIN_ATTESTATION),
)
# Crosslink data root is zero (to be removed in phase 1)
assert attestation.data.crosslink_data_root == ZERO_HASH
# Apply the attestation
# Cache pending attestation
pending_attestation = PendingAttestation(
data=attestation.data,
aggregation_bitfield=attestation.aggregation_bitfield,
custody_bitfield=attestation.custody_bitfield,
inclusion_slot=state.slot
)
if slot_to_epoch(attestation.data.slot) == get_current_epoch(state):
if target_epoch == get_current_epoch(state):
state.current_epoch_attestations.append(pending_attestation)
elif slot_to_epoch(attestation.data.slot) == get_previous_epoch(state):
else:
state.previous_epoch_attestations.append(pending_attestation)
```