nimbus-eth2/beacon_chain/attestation_aggregation.nim

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# beacon_chain
# Copyright (c) 2019-2020 Status Research & Development GmbH
# Licensed and distributed under either of
# * MIT license (license terms in the root directory or at http://opensource.org/licenses/MIT).
# * Apache v2 license (license terms in the root directory or at http://www.apache.org/licenses/LICENSE-2.0).
# at your option. This file may not be copied, modified, or distributed except according to those terms.
{.push raises: [Defect].}
import
std/[options, sequtils, sets],
chronos, chronicles,
./spec/[
beaconstate, datatypes, crypto, digest, helpers, network, signatures],
./block_pools/[spec_cache, chain_dag, quarantine, spec_cache],
./attestation_pool, ./beacon_node_types, ./ssz, ./time
logScope:
topics = "att_aggr"
# https://github.com/ethereum/eth2.0-specs/blob/v1.0.0/specs/phase0/validator.md#aggregation-selection
func is_aggregator*(committee_len: uint64, slot_signature: ValidatorSig): bool =
let
modulo = max(1'u64, committee_len div TARGET_AGGREGATORS_PER_COMMITTEE)
bytes_to_uint64(eth2digest(
slot_signature.toRaw()).data.toOpenArray(0, 7)) mod modulo == 0
func is_aggregator(epochRef: EpochRef, slot: Slot, index: CommitteeIndex,
slot_signature: ValidatorSig): bool =
let
committee_len = get_beacon_committee_len(epochRef, slot, index)
return is_aggregator(committee_len, slot_signature)
proc aggregate_attestations*(
pool: AttestationPool, epochRef: EpochRef, slot: Slot, index: CommitteeIndex,
validatorIndex: ValidatorIndex, slot_signature: ValidatorSig): Option[AggregateAndProof] =
doAssert validatorIndex in get_beacon_committee(epochRef, slot, index)
doAssert index.uint64 < get_committee_count_per_slot(epochRef)
# TODO for testing purposes, refactor this into the condition check
# and just calculation
# https://github.com/ethereum/eth2.0-specs/blob/v1.0.0/specs/phase0/validator.md#aggregation-selection
if not is_aggregator(epochRef, slot, index, slot_signature):
return none(AggregateAndProof)
let maybe_slot_attestation = getAggregatedAttestation(pool, slot, index)
if maybe_slot_attestation.isNone:
return none(AggregateAndProof)
# https://github.com/ethereum/eth2.0-specs/blob/v1.0.0/specs/phase0/validator.md#construct-aggregate
# https://github.com/ethereum/eth2.0-specs/blob/v1.0.0/specs/phase0/validator.md#aggregateandproof
some(AggregateAndProof(
aggregator_index: validatorIndex.uint64,
aggregate: maybe_slot_attestation.get,
selection_proof: slot_signature))
func check_attestation_block_slot(
pool: AttestationPool, attestationSlot: Slot, attestationBlck: BlockRef):
Result[void, (ValidationResult, cstring)] =
# If we allow voting for very old blocks, the state transaction below will go
# nuts and keep processing empty slots
if not (attestationBlck.slot > pool.chainDag.finalizedHead.slot):
return err((ValidationResult.Ignore, cstring(
"Voting for already-finalized block")))
# we'll also cap it at 4 epochs which is somewhat arbitrary, but puts an
# upper bound on the processing done to validate the attestation
# TODO revisit with less arbitrary approach
if not (attestationSlot >= attestationBlck.slot):
return err((ValidationResult.Ignore, cstring(
"Voting for block that didn't exist at the time")))
if not ((attestationSlot - attestationBlck.slot) <= uint64(4 * SLOTS_PER_EPOCH)):
return err((ValidationResult.Ignore, cstring("Voting for very old block")))
ok()
func check_propagation_slot_range(
data: AttestationData, wallTime: BeaconTime):
Result[void, (ValidationResult, cstring)] =
let
futureSlot = (wallTime + MAXIMUM_GOSSIP_CLOCK_DISPARITY).toSlot()
if not futureSlot.afterGenesis or data.slot > futureSlot.slot:
return err((ValidationResult.Ignore, cstring(
"Attestation slot in the future")))
let
pastSlot = (wallTime - MAXIMUM_GOSSIP_CLOCK_DISPARITY).toSlot()
# https://github.com/ethereum/eth2.0-specs/blob/v1.0.0/specs/phase0/p2p-interface.md#configuration
# The spec value of ATTESTATION_PROPAGATION_SLOT_RANGE is 32, but it can
# retransmit attestations on the cusp of being out of spec, and which by
# the time they reach their destination might be out of spec.
const ATTESTATION_PROPAGATION_SLOT_RANGE = 28
if pastSlot.afterGenesis and
data.slot + ATTESTATION_PROPAGATION_SLOT_RANGE < pastSlot.slot:
return err((ValidationResult.Ignore, cstring(
"Attestation slot in the past")))
ok()
func check_attestation_beacon_block(
pool: var AttestationPool, attestation: Attestation):
Result[void, (ValidationResult, cstring)] =
# The block being voted for (attestation.data.beacon_block_root) passes
# validation.
# We rely on the chain DAG to have been validated, so check for the existence
# of the block in the pool.
let attestationBlck = pool.chainDag.getRef(attestation.data.beacon_block_root)
if attestationBlck.isNil:
pool.quarantine.addMissing(attestation.data.beacon_block_root)
return err((ValidationResult.Ignore, cstring("Attestation block unknown")))
# Not in spec - check that rewinding to the state is sane
? check_attestation_block_slot(pool, attestation.data.slot, attestationBlck)
ok()
func check_aggregation_count(
attestation: Attestation, singular: bool):
Result[void, (ValidationResult, cstring)] =
var onesCount = 0
# TODO a cleverer algorithm, along the lines of countOnes() in nim-stew
# But that belongs in nim-stew, since it'd break abstraction layers, to
# use details of its representation from nimbus-eth2.
for aggregation_bit in attestation.aggregation_bits:
if not aggregation_bit:
continue
onesCount += 1
if singular: # More than one ok
if onesCount > 1:
return err((ValidationResult.Reject, cstring(
"Attestation has too many aggregation bits")))
else:
break # Found the one we needed
if onesCount < 1:
return err((ValidationResult.Reject, cstring(
"Attestation has too few aggregation bits")))
ok()
func check_attestation_subnet(
epochRef: EpochRef, attestation: Attestation,
topicCommitteeIndex: uint64): Result[void, (ValidationResult, cstring)] =
let
expectedSubnet =
compute_subnet_for_attestation(
get_committee_count_per_slot(epochRef),
attestation.data.slot, attestation.data.index.CommitteeIndex)
if expectedSubnet != topicCommitteeIndex:
return err((ValidationResult.Reject, cstring(
"Attestation's committee index not for the correct subnet")))
ok()
# https://github.com/ethereum/eth2.0-specs/blob/v1.0.0/specs/phase0/p2p-interface.md#beacon_attestation_subnet_id
proc validateAttestation*(
pool: var AttestationPool,
attestation: Attestation, wallTime: BeaconTime,
topicCommitteeIndex: uint64):
Result[HashSet[ValidatorIndex], (ValidationResult, cstring)] =
# [REJECT] The attestation's epoch matches its target -- i.e.
# attestation.data.target.epoch ==
# compute_epoch_at_slot(attestation.data.slot)
block:
let v = check_attestation_slot_target(attestation.data)
if v.isErr():
return err((ValidationResult.Reject, v.error))
# attestation.data.slot is within the last ATTESTATION_PROPAGATION_SLOT_RANGE
# slots (within a MAXIMUM_GOSSIP_CLOCK_DISPARITY allowance) -- i.e.
# attestation.data.slot + ATTESTATION_PROPAGATION_SLOT_RANGE >= current_slot
# >= attestation.data.slot (a client MAY queue future attestations for
# processing at the appropriate slot).
? check_propagation_slot_range(attestation.data, wallTime) # [IGNORE]
# The attestation is unaggregated -- that is, it has exactly one
# participating validator (len([bit for bit in attestation.aggregation_bits
# if bit == 0b1]) == 1).
? check_aggregation_count(attestation, singular = true) # [REJECT]
let tgtBlck = pool.chainDag.getRef(attestation.data.target.root)
if tgtBlck.isNil:
pool.quarantine.addMissing(attestation.data.target.root)
return err((ValidationResult.Ignore, cstring(
"Attestation target block unknown")))
# The following rule follows implicitly from that we clear out any
# unviable blocks from the chain dag:
#
# The current finalized_checkpoint is an ancestor of the block defined by
# attestation.data.beacon_block_root -- i.e. get_ancestor(store,
# attestation.data.beacon_block_root,
# compute_start_slot_at_epoch(store.finalized_checkpoint.epoch)) ==
# store.finalized_checkpoint.root
let epochRef = pool.chainDag.getEpochRef(
tgtBlck, attestation.data.target.epoch)
# [REJECT] The committee index is within the expected range -- i.e.
# data.index < get_committee_count_per_slot(state, data.target.epoch).
if not (attestation.data.index < get_committee_count_per_slot(epochRef)):
return err((ValidationResult.Reject, cstring(
"validateAttestation: committee index not within expected range")))
# [REJECT] The attestation is for the correct subnet -- i.e.
# compute_subnet_for_attestation(committees_per_slot,
# attestation.data.slot, attestation.data.index) == subnet_id, where
# committees_per_slot = get_committee_count_per_slot(state,
# attestation.data.target.epoch), which may be pre-computed along with the
# committee information for the signature check.
? check_attestation_subnet(epochRef, attestation, topicCommitteeIndex)
# [REJECT] The number of aggregation bits matches the committee size -- i.e.
# len(attestation.aggregation_bits) == len(get_beacon_committee(state,
# data.slot, data.index)).
#
# This uses the same epochRef as data.target.epoch, because the attestation's
# epoch matches its target and attestation.data.target.root is an ancestor of
# attestation.data.beacon_block_root.
if not (attestation.aggregation_bits.lenu64 == get_beacon_committee_len(
epochRef, attestation.data.slot, attestation.data.index.CommitteeIndex)):
return err((ValidationResult.Reject, cstring(
"validateAttestation: number of aggregation bits and committee size mismatch")))
# The block being voted for (attestation.data.beacon_block_root) has been seen
# (via both gossip and non-gossip sources) (a client MAY queue aggregates for
# processing once block is retrieved).
# The block being voted for (attestation.data.beacon_block_root) passes
# validation.
? check_attestation_beacon_block(pool, attestation) # [IGNORE/REJECT]
let
fork = pool.chainDag.headState.data.data.fork
genesis_validators_root =
pool.chainDag.headState.data.data.genesis_validators_root
attesting_indices = get_attesting_indices(
epochRef, attestation.data, attestation.aggregation_bits)
# The number of aggregation bits matches the committee size, which ensures
# this condition holds.
doAssert attesting_indices.len == 1, "Per bits check above"
let validator_index = toSeq(attesting_indices)[0]
# There has been no other valid attestation seen on an attestation subnet
# that has an identical `attestation.data.target.epoch` and participating
# validator index.
# Slightly modified to allow only newer attestations than were previously
# seen (no point in propagating older votes)
if (pool.nextAttestationEpoch.lenu64.ValidatorIndex > validator_index) and
pool.nextAttestationEpoch[validator_index].subnet >
attestation.data.target.epoch:
return err((ValidationResult.Ignore, cstring(
"Validator has already voted in epoch")))
# The signature of attestation is valid.
block:
let v = is_valid_indexed_attestation(
fork, genesis_validators_root, epochRef, attesting_indices,
attestation, {})
if v.isErr():
return err((ValidationResult.Reject, v.error))
# [REJECT] The attestation's target block is an ancestor of the block named
# in the LMD vote -- i.e. get_ancestor(store,
# attestation.data.beacon_block_root,
# compute_start_slot_at_epoch(attestation.data.target.epoch)) ==
# attestation.data.target.root
let attestationBlck = pool.chainDag.getRef(attestation.data.beacon_block_root)
# already checked in check_attestation_beacon_block()
doAssert not attestationBlck.isNil
if not (get_ancestor(attestationBlck,
compute_start_slot_at_epoch(attestation.data.target.epoch),
SLOTS_PER_EPOCH.int).root ==
attestation.data.target.root):
return err((ValidationResult.Reject, cstring(
"validateAttestation: attestation's target block not an ancestor of LMD vote block")))
# Only valid attestations go in the list
if not (pool.nextAttestationEpoch.lenu64.ValidatorIndex > validator_index):
pool.nextAttestationEpoch.setLen(validator_index.int + 1)
pool.nextAttestationEpoch[validator_index].subnet =
attestation.data.target.epoch + 1
ok(attesting_indices)
# https://github.com/ethereum/eth2.0-specs/blob/v1.0.0/specs/phase0/p2p-interface.md#beacon_aggregate_and_proof
proc validateAggregate*(
pool: var AttestationPool,
signedAggregateAndProof: SignedAggregateAndProof, wallTime: BeaconTime):
Result[HashSet[ValidatorIndex], (ValidationResult, cstring)] =
let
aggregate_and_proof = signedAggregateAndProof.message
aggregate = aggregate_and_proof.aggregate
# [IGNORE] aggregate.data.slot is within the last
# ATTESTATION_PROPAGATION_SLOT_RANGE slots (with a
# MAXIMUM_GOSSIP_CLOCK_DISPARITY allowance) -- i.e. aggregate.data.slot +
# ATTESTATION_PROPAGATION_SLOT_RANGE >= current_slot >= aggregate.data.slot
? check_propagation_slot_range(aggregate.data, wallTime) # [IGNORE]
# [REJECT] The aggregate attestation's epoch matches its target -- i.e.
# `aggregate.data.target.epoch == compute_epoch_at_slot(aggregate.data.slot)`
block:
let v = check_attestation_slot_target(aggregate.data)
if v.isErr():
return err((ValidationResult.Reject, v.error))
# [IGNORE] The valid aggregate attestation defined by
# hash_tree_root(aggregate) has not already been seen (via aggregate gossip,
# within a verified block, or through the creation of an equivalent aggregate
# locally).
#
# This is [IGNORE] and already checked by attestation pool when aggregate is
# added.
# [IGNORE] The aggregate is the first valid aggregate received for the
# aggregator with index aggregate_and_proof.aggregator_index for the epoch
# aggregate.data.target.epoch.
# Slightly modified to allow only newer attestations than were previously
# seen (no point in propagating older votes)
if (pool.nextAttestationEpoch.lenu64 >
aggregate_and_proof.aggregator_index) and
pool.nextAttestationEpoch[
aggregate_and_proof.aggregator_index].aggregate >
aggregate.data.target.epoch:
return err((ValidationResult.Ignore, cstring(
"Validator has already aggregated in epoch")))
# [REJECT] The attestation has participants -- that is,
# len(get_attesting_indices(state, aggregate.data, aggregate.aggregation_bits)) >= 1.
#
# get_attesting_indices() is:
# committee = get_beacon_committee(state, data.slot, data.index)
# return set(index for i, index in enumerate(committee) if bits[i])
#
# the attestation doesn't have participants is iff either:
# (1) the aggregation bits are all 0; or
# (2) the non-zero aggregation bits don't overlap with extant committee
# members, i.e. they counts don't match.
# But (2) would reflect an invalid aggregation in other ways, so reject it
# either way.
? check_aggregation_count(aggregate, singular = false)
# [REJECT] The block being voted for (aggregate.data.beacon_block_root)
# passes validation.
? check_attestation_beacon_block(pool, aggregate)
# [REJECT] aggregate_and_proof.selection_proof selects the validator as an
# aggregator for the slot -- i.e. is_aggregator(state, aggregate.data.slot,
# aggregate.data.index, aggregate_and_proof.selection_proof) returns True.
let tgtBlck = pool.chainDag.getRef(aggregate.data.target.root)
if tgtBlck.isNil:
pool.quarantine.addMissing(aggregate.data.target.root)
return err((ValidationResult.Ignore, cstring(
"Aggregate target block unknown")))
let epochRef = pool.chainDag.getEpochRef(tgtBlck, aggregate.data.target.epoch)
if not is_aggregator(
epochRef, aggregate.data.slot, aggregate.data.index.CommitteeIndex,
aggregate_and_proof.selection_proof):
return err((ValidationResult.Reject, cstring("Incorrect aggregator")))
# [REJECT] The aggregator's validator index is within the committee -- i.e.
# aggregate_and_proof.aggregator_index in get_beacon_committee(state,
# aggregate.data.slot, aggregate.data.index).
if aggregate_and_proof.aggregator_index.ValidatorIndex notin
get_beacon_committee(
epochRef, aggregate.data.slot, aggregate.data.index.CommitteeIndex):
return err((ValidationResult.Reject, cstring(
"Aggregator's validator index not in committee")))
# [REJECT] The aggregate_and_proof.selection_proof is a valid signature of the
# aggregate.data.slot by the validator with index
# aggregate_and_proof.aggregator_index.
# get_slot_signature(state, aggregate.data.slot, privkey)
if aggregate_and_proof.aggregator_index >= epochRef.validator_keys.lenu64:
return err((ValidationResult.Reject, cstring("Invalid aggregator_index")))
let
fork = pool.chainDag.headState.data.data.fork
genesis_validators_root =
pool.chainDag.headState.data.data.genesis_validators_root
if not verify_slot_signature(
fork, genesis_validators_root, aggregate.data.slot,
epochRef.validator_keys[aggregate_and_proof.aggregator_index],
aggregate_and_proof.selection_proof):
return err((ValidationResult.Reject, cstring(
"Selection_proof signature verification failed")))
# [REJECT] The aggregator signature, signed_aggregate_and_proof.signature, is valid.
if not verify_aggregate_and_proof_signature(
fork, genesis_validators_root, aggregate_and_proof,
epochRef.validator_keys[aggregate_and_proof.aggregator_index],
signed_aggregate_and_proof.signature):
return err((ValidationResult.Reject, cstring(
"signed_aggregate_and_proof signature verification failed")))
let attesting_indices = get_attesting_indices(
epochRef, aggregate.data, aggregate.aggregation_bits)
# [REJECT] The signature of aggregate is valid.
block:
let v = is_valid_indexed_attestation(
fork, genesis_validators_root, epochRef, attesting_indices,
aggregate, {})
if v.isErr():
return err((ValidationResult.Reject, v.error))
# The following rule follows implicitly from that we clear out any
# unviable blocks from the chain dag:
#
# The current finalized_checkpoint is an ancestor of the block defined by
# aggregate.data.beacon_block_root -- i.e. get_ancestor(store,
# aggregate.data.beacon_block_root,
# compute_start_slot_at_epoch(store.finalized_checkpoint.epoch)) ==
# store.finalized_checkpoint.root
# Only valid aggregates go in the list
if pool.nextAttestationEpoch.lenu64 <= aggregate_and_proof.aggregator_index:
pool.nextAttestationEpoch.setLen(
aggregate_and_proof.aggregator_index.int + 1)
pool.nextAttestationEpoch[aggregate_and_proof.aggregator_index].aggregate =
aggregate.data.target.epoch + 1
ok(attesting_indices)