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nimbus-eth2/beacon_chain/gossip_processing/batch_validation.nim

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# beacon_chain
# Copyright (c) 2019-2021 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/[deques, sequtils],
metrics,
# Status
chronicles, chronos,
../spec/signatures_batch,
../consensus_object_pools/[blockchain_dag, spec_cache]
export signatures_batch, blockchain_dag
logScope:
topics = "gossip_checks"
declareCounter batch_verification_batches,
"Total number of batches processed"
declareCounter batch_verification_signatures,
"Total number of verified signatures before aggregation"
declareCounter batch_verification_aggregates,
"Total number of verified signatures after aggregation"
# Batched gossip validation
# ----------------------------------------------------------------
# Batching in the context of BLS means collecting the signatures of several
# messages and verifying them all at once - this can be done more efficiently
# than verifying each message one by one, but the downside is that we get an
# all-or-nothing response - in case of an invalid signature, we must re-check
# each message separately.
#
# In addition to batching, we also perform lazy aggregation:
#
# * batching speeds up the verification of multiple signatures over different
# messages, by a decent amount
# * lazy aggregation speeds up the verification of multiple signatures over the
# same message, by a lot
#
# Due to the nature of gossip validation in eth2, it is common for messages
# to arrive in bursts - because most traffic on the network is valid (honest
# nodes don't re-broadcast invalid traffic and dishonest nodes quickly get
# disconnected), valid messages by far make up the bulk of traffic.
#
# Further, traffic is divided into topics - on a single topic it will be
# highly likely that the same message appears over and over again, but with
# different signatures, as most validators have the same view of the network -
# at least 2/3 or we're in deep trouble :)
type
BatchResult* {.pure.} = enum
Invalid # Invalid by default
Valid
Timeout
Eager = proc(): bool {.gcsafe, raises: [Defect].} ##\
## Callback that returns true if eager processing should be done to lower
## latency at the expense of spending more cycles validating things, creating
## a crude timesharing priority mechanism.
BatchItem* = object
sigset: SignatureSet
fut: Future[BatchResult]
Batch* = object
created: Moment
sigsets: seq[SignatureSet]
items: seq[BatchItem]
BatchCrypto* = object
# Each batch is bounded by BatchedCryptoSize which was chosen:
# - based on "nimble bench" in nim-blscurve
# so that low power devices like Raspberry Pi 4 can process
# that many batched verifications within ~30ms on average
# - based on the accumulation rate of attestations and aggregates
# in large instances which were 12000 per slot (12s)
# hence 1 per ms (but the pattern is bursty around the 4s mark)
# The number of batches is bounded by time - batch validation is skipped if
# we can't process them in the time that one slot takes, and we return
# timeout instead which prevents the gossip layer from forwarding the
# batch.
batches: Deque[ref Batch]
eager: Eager ##\
## Eager is used to enable eager processing of attestations when it's
## prudent to do so (instead of leaving the CPU for other, presumably more
## important work like block processing)
##
verifier: BatchVerifier
pruneTime: Moment ## last time we had to prune something
# `nim-metrics` library is a bit too slow to update on every batch, so
# we accumulate here instead
counts: tuple[signatures, batches, aggregates: int64]
const
# We cap waiting for an idle slot in case there's a lot of network traffic
# taking up all CPU - we don't want to _completely_ stop processing
# attestations - doing so also allows us to benefit from more batching /
# larger network reads when under load.
BatchAttAccumTime = 10.milliseconds
# Threshold for immediate trigger of batch verification.
# A balance between throughput and worst case latency.
# At least 6 so that the constant factors
# (RNG for blinding and Final Exponentiation)
# are amortized, but not too big as we need to redo checks one-by-one if one
# failed.
# The current value is based on experiments, where 72 gives an average batch
# size of ~30 signatures per batch, or 2.5 signatures per aggregate (meaning
# an average of 12 verifications per batch which on a raspberry should be
# doable in less than 30ms). In the same experiment, a value of 36 resulted
# in 17-18 signatures per batch and 1.7-1.9 signatures per aggregate - this
# node was running on mainnet with `--subscribe-all-subnets` turned on -
# typical nodes will see smaller batches.
BatchedCryptoSize = 72
proc new*(
T: type BatchCrypto, rng: ref BrHmacDrbgContext,
eager: Eager, taskpool: TaskPoolPtr): ref BatchCrypto =
(ref BatchCrypto)(
verifier: BatchVerifier(rng: rng, taskpool: taskpool),
eager: eager,
pruneTime: Moment.now())
func len(batch: Batch): int =
batch.items.len()
func full(batch: Batch): bool =
batch.len() >= BatchedCryptoSize
proc complete(batchItem: var BatchItem, v: BatchResult) =
batchItem.fut.complete(v)
batchItem.fut = nil
proc complete(batchItem: var BatchItem, ok: bool) =
batchItem.fut.complete(if ok: BatchResult.Valid else: BatchResult.Invalid)
batchItem.fut = nil
proc skip(batch: var Batch) =
for res in batch.items.mitems():
res.complete(BatchResult.Timeout)
proc pruneBatchQueue(batchCrypto: ref BatchCrypto) =
let
now = Moment.now()
# If batches haven't been processed for more than 12 seconds
while batchCrypto.batches.len() > 0:
if batchCrypto.batches[0][].created + SECONDS_PER_SLOT.int64.seconds > now:
break
if batchCrypto.pruneTime + SECONDS_PER_SLOT.int64.seconds > now:
notice "Batch queue pruned, skipping attestation validation",
batches = batchCrypto.batches.len()
batchCrypto.pruneTime = Moment.now()
batchCrypto.batches.popFirst()[].skip()
proc combine(a: var Signature, b: Signature) =
var tmp = AggregateSignature.init(CookedSig(a))
tmp.aggregate(b)
a = Signature(tmp.finish())
proc combine(a: var PublicKey, b: PublicKey) =
var tmp = AggregatePublicKey.init(CookedPubKey(a))
tmp.aggregate(b)
a = PublicKey(tmp.finish())
proc processBatch(batchCrypto: ref BatchCrypto) =
## Process one batch, if there is any
# Pruning the queue here makes sure we catch up with processing if need be
batchCrypto.pruneBatchQueue() # Skip old batches
if batchCrypto[].batches.len() == 0:
# No more batches left, they might have been eagerly processed or pruned
return
let
batch = batchCrypto[].batches.popFirst()
batchSize = batch[].sigsets.len()
if batchSize == 0:
# Nothing to do in this batch, can happen when a batch is created without
# there being any signatures successfully added to it
discard
else:
trace "batch crypto - starting",
batchSize
let
startTick = Moment.now()
ok =
if batchSize == 1: blsVerify(batch[].sigsets[0])
else: batchCrypto.verifier.batchVerify(batch[].sigsets)
trace "batch crypto - finished",
batchSize,
cryptoVerified = ok,
batchDur = Moment.now() - startTick
if ok:
for res in batch.items.mitems():
res.complete(BatchResult.Valid)
else:
# Batched verification failed meaning that some of the signature checks
# failed, but we don't know which ones - check each signature separately
# instead
debug "batch crypto - failure, falling back",
items = batch[].items.len()
for item in batch[].items.mitems():
item.complete(blsVerify item.sigset)
batchCrypto[].counts.batches += 1
batchCrypto[].counts.signatures += batch[].items.len()
batchCrypto[].counts.aggregates += batch[].sigsets.len()
if batchCrypto[].counts.batches >= 256:
# Not too often, so as not to overwhelm our metrics
batch_verification_batches.inc(batchCrypto[].counts.batches)
batch_verification_signatures.inc(batchCrypto[].counts.signatures)
batch_verification_aggregates.inc(batchCrypto[].counts.aggregates)
reset(batchCrypto[].counts)
proc deferCryptoProcessing(batchCrypto: ref BatchCrypto) {.async.} =
## Process pending crypto check after some time has passed - the time is
## chosen such that there's time to fill the batch but not so long that
## latency across the network is negatively affected
await sleepAsync(BatchAttAccumTime)
# Take the first batch in the queue and process it - if eager processing has
# stolen it already, that's fine
batchCrypto.processBatch()
proc getBatch(batchCrypto: ref BatchCrypto): (ref Batch, bool) =
# Get a batch suitable for attestation processing - in particular, attestation
# batches might be skipped
batchCrypto.pruneBatchQueue()
if batchCrypto.batches.len() == 0 or
batchCrypto.batches.peekLast[].full():
# There are no batches in progress - start a new batch and schedule a
# deferred task to eventually handle it
let batch = (ref Batch)(created: Moment.now())
batchCrypto[].batches.addLast(batch)
(batch, true)
else:
let batch = batchCrypto[].batches.peekLast()
# len will be 0 when the batch was created but nothing added to it
# because of early failures
(batch, batch[].len() == 0)
proc scheduleBatch(batchCrypto: ref BatchCrypto, fresh: bool) =
if fresh:
# Every time we start a new round of batching, we need to launch a deferred
# task that will compute the result of the batch eventually in case the
# batch is never filled or eager processing is blocked
asyncSpawn batchCrypto.deferCryptoProcessing()
if batchCrypto.batches.len() > 0 and
batchCrypto.batches.peekFirst()[].full() and
batchCrypto.eager():
# If there's a full batch, process it eagerly assuming the callback allows
batchCrypto.processBatch()
template orReturnErr(v: Option, error: cstring): untyped =
## Returns with given error string if the option does not have a value
let tmp = v
if tmp.isNone:
return err(error) # this exits the calling scope, as templates are inlined.
tmp.unsafeGet()
template withBatch(
batchCrypto: ref BatchCrypto, name: cstring,
body: untyped): Future[BatchResult] =
block:
let
(batch, fresh) = batchCrypto.getBatch()
let
fut = newFuture[BatchResult](name)
sigset = body
var found = false
# Find existing signature sets with the same message - if we can verify an
# aggregate instead of several signatures, that is _much_ faster
for item in batch[].sigsets.mitems():
if item.message == sigset.message:
item.signature.combine(sigset.signature)
item.pubkey.combine(sigset.pubkey)
found = true
break
if not found:
batch[].sigsets.add sigset
# We need to keep the "original" sigset to allow verifying each signature
# one by one in the case the combined operation fails
batch[].items.add(BatchItem(sigset: sigset, fut: fut))
batchCrypto.scheduleBatch(fresh)
fut
# See also verify_attestation_signature
proc scheduleAttestationCheck*(
batchCrypto: ref BatchCrypto,
fork: Fork, genesis_validators_root: Eth2Digest,
attestationData: AttestationData,
pubkey: CookedPubKey, signature: ValidatorSig
): Result[tuple[fut: Future[BatchResult], sig: CookedSig], cstring] =
## Schedule crypto verification of an attestation
##
## The buffer is processed:
## - when eager processing is enabled and the batch is full
## - otherwise after 10ms (BatchAttAccumTime)
##
## This returns an error if crypto sanity checks failed
## and a future with the deferred attestation check otherwise.
##
let
sig = signature.load().orReturnErr("attestation: cannot load signature")
fut = batchCrypto.withBatch("batch_validation.scheduleAttestationCheck"):
attestation_signature_set(
fork, genesis_validators_root, attestationData, pubkey, sig)
ok((fut, sig))
proc scheduleAggregateChecks*(
batchCrypto: ref BatchCrypto,
fork: Fork, genesis_validators_root: Eth2Digest,
signedAggregateAndProof: SignedAggregateAndProof,
epochRef: EpochRef,
attesting_indices: openArray[ValidatorIndex]
): Result[tuple[
aggregatorFut, slotFut, aggregateFut: Future[BatchResult],
sig: CookedSig], cstring] =
## Schedule crypto verification of an aggregate
##
## This involves 3 checks:
## - verify_slot_signature
## - verify_aggregate_and_proof_signature
## - is_valid_indexed_attestation
##
## The buffer is processed:
## - when eager processing is enabled and the batch is full
## - otherwise after 10ms (BatchAttAccumTime)
##
## This returns None if the signatures could not be loaded.
## and 3 futures with the deferred aggregate checks otherwise.
template aggregate_and_proof: untyped = signedAggregateAndProof.message
template aggregate: untyped = aggregate_and_proof.aggregate
# Do the eager steps first to avoid polluting batches with needlessly
let
aggregatorKey =
epochRef.validatorKey(aggregate_and_proof.aggregator_index).orReturnErr(
"SignedAggregateAndProof: invalid aggregator index")
aggregatorSig = signedAggregateAndProof.signature.load().orReturnErr(
"aggregateAndProof: invalid proof signature")
slotSig = aggregate_and_proof.selection_proof.load().orReturnErr(
"aggregateAndProof: invalid selection signature")
aggregateKey = ? aggregateAll(epochRef.dag, attesting_indices)
aggregateSig = aggregate.signature.load().orReturnErr(
"aggregateAndProof: invalid aggregate signature")
let
aggregatorFut = batchCrypto.withBatch("scheduleAggregateChecks.aggregator"):
aggregate_and_proof_signature_set(
fork, genesis_validators_root, aggregate_and_proof, aggregatorKey,
aggregatorSig)
slotFut = batchCrypto.withBatch("scheduleAggregateChecks.selection_proof"):
slot_signature_set(
fork, genesis_validators_root, aggregate.data.slot, aggregatorKey,
slotSig)
aggregateFut = batchCrypto.withBatch("scheduleAggregateChecks.aggregate"):
attestation_signature_set(
fork, genesis_validators_root, aggregate.data, aggregateKey,
aggregateSig)
ok((aggregatorFut, slotFut, aggregateFut, aggregateSig))
proc scheduleSyncCommitteeMessageCheck*(
batchCrypto: ref BatchCrypto,
fork: Fork, genesis_validators_root: Eth2Digest,
slot: Slot, beacon_block_root: Eth2Digest,
pubkey: CookedPubKey, signature: ValidatorSig
): Result[tuple[fut: Future[BatchResult], sig: CookedSig], cstring] =
## Schedule crypto verification of an attestation
##
## The buffer is processed:
## - when eager processing is enabled and the batch is full
## - otherwise after 10ms (BatchAttAccumTime)
##
## This returns an error if crypto sanity checks failed
## and a future with the deferred attestation check otherwise.
##
let
sig = signature.load().orReturnErr(
"SyncCommitteMessage: cannot load signature")
fut = batchCrypto.withBatch("scheduleSyncCommitteeMessageCheck"):
sync_committee_message_signature_set(
fork, genesis_validators_root, slot, beacon_block_root, pubkey, sig)
ok((fut, sig))
proc scheduleContributionChecks*(
batchCrypto: ref BatchCrypto,
fork: Fork, genesis_validators_root: Eth2Digest,
signedContributionAndProof: SignedContributionAndProof,
subcommitteeIdx: SyncSubcommitteeIndex,
dag: ChainDAGRef): Result[tuple[
aggregatorFut, proofFut, contributionFut: Future[BatchResult],
sig: CookedSig], cstring] =
## Schedule crypto verification of all signatures in a
## SignedContributionAndProof message
##
## The buffer is processed:
## - when eager processing is enabled and the batch is full
## - otherwise after 10ms (BatchAttAccumTime)
##
## This returns an error if crypto sanity checks failed
## and a future with the deferred check otherwise.
##
template contribution_and_proof: untyped = signedContributionAndProof.message
template contribution: untyped = contribution_and_proof.contribution
# Do the eager steps first to avoid polluting batches with needlessly
let
aggregatorKey =
dag.validatorKey(contribution_and_proof.aggregator_index).orReturnErr(
"SignedAggregateAndProof: invalid contributor index")
aggregatorSig = signedContributionAndProof.signature.load().orReturnErr(
"SignedContributionAndProof: invalid proof signature")
proofSig = contribution_and_proof.selection_proof.load().orReturnErr(
"SignedContributionAndProof: invalid selection signature")
contributionSig = contribution.signature.load().orReturnErr(
"SignedContributionAndProof: invalid contribution signature")
contributionKey = ? aggregateAll(
dag, dag.syncCommitteeParticipants(contribution.slot, subcommitteeIdx),
contribution.aggregation_bits)
let
aggregatorFut = batchCrypto.withBatch("scheduleContributionAndProofChecks.aggregator"):
contribution_and_proof_signature_set(
fork, genesis_validators_root, contribution_and_proof, aggregatorKey,
aggregatorSig)
proofFut = batchCrypto.withBatch("scheduleContributionAndProofChecks.selection_proof"):
sync_committee_selection_proof_set(
fork, genesis_validators_root, contribution.slot,
contribution.subcommittee_index, aggregatorKey, proofSig)
contributionFut = batchCrypto.withBatch("scheduleContributionAndProofChecks.contribution"):
sync_committee_message_signature_set(
fork, genesis_validators_root, contribution.slot,
contribution.beacon_block_root, contributionKey, contributionSig)
ok((aggregatorFut, proofFut, contributionFut, contributionSig))
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