nimbus-eth2/beacon_chain/spec/light_client_sync.nim

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# beacon_chain
# Copyright (c) 2021-2023 Status Research & Development GmbH
# Licensed and distributed under either of
# * MIT license (license terms in the root directory or at https://opensource.org/licenses/MIT).
# * Apache v2 license (license terms in the root directory or at https://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: [].}
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import
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stew/[bitops2, objects],
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datatypes/altair,
helpers
from ../consensus_object_pools/block_pools_types import VerifierError
export block_pools_types.VerifierError
# https://github.com/ethereum/consensus-specs/blob/v1.4.0-alpha.3/specs/altair/light-client/sync-protocol.md#initialize_light_client_store
func initialize_light_client_store*(
trusted_block_root: Eth2Digest,
bootstrap: ForkyLightClientBootstrap,
cfg: RuntimeConfig
): auto =
type ResultType =
Result[typeof(bootstrap).kind.LightClientStore, VerifierError]
if not is_valid_light_client_header(bootstrap.header, cfg):
return ResultType.err(VerifierError.Invalid)
if hash_tree_root(bootstrap.header.beacon) != trusted_block_root:
return ResultType.err(VerifierError.Invalid)
if not is_valid_merkle_branch(
hash_tree_root(bootstrap.current_sync_committee),
bootstrap.current_sync_committee_branch,
log2trunc(altair.CURRENT_SYNC_COMMITTEE_INDEX),
get_subtree_index(altair.CURRENT_SYNC_COMMITTEE_INDEX),
bootstrap.header.beacon.state_root):
return ResultType.err(VerifierError.Invalid)
return ResultType.ok(typeof(bootstrap).kind.LightClientStore(
finalized_header: bootstrap.header,
current_sync_committee: bootstrap.current_sync_committee,
optimistic_header: bootstrap.header))
# https://github.com/ethereum/consensus-specs/blob/v1.4.0-alpha.3/specs/altair/light-client/sync-protocol.md#validate_light_client_update
proc validate_light_client_update*(
store: ForkyLightClientStore,
update: SomeForkyLightClientUpdate,
current_slot: Slot,
cfg: RuntimeConfig,
genesis_validators_root: Eth2Digest): Result[void, VerifierError] =
# Verify sync committee has sufficient participants
template sync_aggregate(): auto = update.sync_aggregate
template sync_committee_bits(): auto = sync_aggregate.sync_committee_bits
let num_active_participants = countOnes(sync_committee_bits).uint64
if num_active_participants < MIN_SYNC_COMMITTEE_PARTICIPANTS:
return err(VerifierError.Invalid)
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# Verify update does not skip a sync committee period
if not is_valid_light_client_header(update.attested_header, cfg):
return err(VerifierError.Invalid)
when update is SomeForkyLightClientUpdateWithFinality:
if update.attested_header.beacon.slot < update.finalized_header.beacon.slot:
return err(VerifierError.Invalid)
if update.signature_slot <= update.attested_header.beacon.slot:
return err(VerifierError.Invalid)
if current_slot < update.signature_slot:
return err(VerifierError.UnviableFork)
let
store_period = store.finalized_header.beacon.slot.sync_committee_period
signature_period = update.signature_slot.sync_committee_period
is_next_sync_committee_known = store.is_next_sync_committee_known
if is_next_sync_committee_known:
if signature_period notin [store_period, store_period + 1]:
return err(VerifierError.MissingParent)
else:
if signature_period != store_period:
return err(VerifierError.MissingParent)
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# Verify update is relevant
let attested_period = update.attested_header.beacon.slot.sync_committee_period
when update is SomeForkyLightClientUpdateWithSyncCommittee:
let is_sync_committee_update = update.is_sync_committee_update
if update.attested_header.beacon.slot <= store.finalized_header.beacon.slot:
when update is SomeForkyLightClientUpdateWithSyncCommittee:
if is_next_sync_committee_known:
return err(VerifierError.Duplicate)
if attested_period != store_period or not is_sync_committee_update:
return err(VerifierError.Duplicate)
else:
return err(VerifierError.Duplicate)
# Verify that the `finality_branch`, if present, confirms `finalized_header`
# to match the finalized checkpoint root saved in the state of
# `attested_header`. Note that the genesis finalized checkpoint root is
# represented as a zero hash.
when update is SomeForkyLightClientUpdateWithFinality:
if not update.is_finality_update:
if update.finalized_header != default(typeof(update.finalized_header)):
return err(VerifierError.Invalid)
else:
var finalized_root {.noinit.}: Eth2Digest
if update.finalized_header.beacon.slot != GENESIS_SLOT:
if not is_valid_light_client_header(update.finalized_header, cfg):
return err(VerifierError.Invalid)
finalized_root = hash_tree_root(update.finalized_header.beacon)
elif update.finalized_header == default(typeof(update.finalized_header)):
finalized_root.reset()
else:
return err(VerifierError.Invalid)
if not is_valid_merkle_branch(
finalized_root,
update.finality_branch,
log2trunc(altair.FINALIZED_ROOT_INDEX),
get_subtree_index(altair.FINALIZED_ROOT_INDEX),
update.attested_header.beacon.state_root):
return err(VerifierError.Invalid)
# Verify that the `next_sync_committee`, if present, actually is the
# next sync committee saved in the state of the `attested_header`
when update is SomeForkyLightClientUpdateWithSyncCommittee:
if not is_sync_committee_update:
if update.next_sync_committee !=
default(typeof(update.next_sync_committee)):
return err(VerifierError.Invalid)
else:
if attested_period == store_period and is_next_sync_committee_known:
if update.next_sync_committee != store.next_sync_committee:
return err(VerifierError.UnviableFork)
if not is_valid_merkle_branch(
hash_tree_root(update.next_sync_committee),
update.next_sync_committee_branch,
log2trunc(altair.NEXT_SYNC_COMMITTEE_INDEX),
get_subtree_index(altair.NEXT_SYNC_COMMITTEE_INDEX),
update.attested_header.beacon.state_root):
return err(VerifierError.Invalid)
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# Verify sync committee aggregate signature
let sync_committee =
if signature_period == store_period:
unsafeAddr store.current_sync_committee
else:
unsafeAddr store.next_sync_committee
var participant_pubkeys =
newSeqOfCap[ValidatorPubKey](num_active_participants)
for idx, bit in sync_aggregate.sync_committee_bits:
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if bit:
participant_pubkeys.add(sync_committee.pubkeys.data[idx])
let
fork_version_slot = max(update.signature_slot, 1.Slot) - 1
fork_version = cfg.forkVersionAtEpoch(fork_version_slot.epoch)
domain = compute_domain(
DOMAIN_SYNC_COMMITTEE, fork_version, genesis_validators_root)
signing_root = compute_signing_root(update.attested_header.beacon, domain)
if not blsFastAggregateVerify(
participant_pubkeys, signing_root.data,
sync_aggregate.sync_committee_signature):
return err(VerifierError.UnviableFork)
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ok()
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# https://github.com/ethereum/consensus-specs/blob/v1.4.0-alpha.3/specs/altair/light-client/sync-protocol.md#apply_light_client_update
func apply_light_client_update(
store: var ForkyLightClientStore,
update: SomeForkyLightClientUpdate): bool =
var didProgress = false
let
store_period = store.finalized_header.beacon.slot.sync_committee_period
finalized_period = update.finalized_header.beacon.slot.sync_committee_period
if not store.is_next_sync_committee_known:
assert finalized_period == store_period
when update is SomeForkyLightClientUpdateWithSyncCommittee:
store.next_sync_committee = update.next_sync_committee
if store.is_next_sync_committee_known:
didProgress = true
elif finalized_period == store_period + 1:
store.current_sync_committee = store.next_sync_committee
when update is SomeForkyLightClientUpdateWithSyncCommittee:
store.next_sync_committee = update.next_sync_committee
else:
store.next_sync_committee.reset()
store.previous_max_active_participants =
store.current_max_active_participants
store.current_max_active_participants = 0
didProgress = true
if update.finalized_header.beacon.slot > store.finalized_header.beacon.slot:
store.finalized_header = update.finalized_header
if store.finalized_header.beacon.slot > store.optimistic_header.beacon.slot:
store.optimistic_header = store.finalized_header
didProgress = true
didProgress
# https://github.com/ethereum/consensus-specs/blob/v1.4.0-alpha.3/specs/altair/light-client/sync-protocol.md#process_light_client_store_force_update
type
ForceUpdateResult* = enum
NoUpdate,
DidUpdateWithoutSupermajority,
DidUpdateWithoutFinality
func process_light_client_store_force_update*(
store: var ForkyLightClientStore,
current_slot: Slot): ForceUpdateResult {.discardable.} =
var res = NoUpdate
if store.best_valid_update.isSome and
current_slot > store.finalized_header.beacon.slot + UPDATE_TIMEOUT:
# Forced best update when the update timeout has elapsed.
# Because the apply logic waits for `finalized_header.beacon.slot`
# to indicate sync committee finality, the `attested_header` may be
# treated as `finalized_header` in extended periods of non-finality
# to guarantee progression into later sync committee periods according
# to `is_better_update`.
template best(): auto = store.best_valid_update.get
if best.finalized_header.beacon.slot <= store.finalized_header.beacon.slot:
best.finalized_header = best.attested_header
if apply_light_client_update(store, best):
template sync_aggregate(): auto = best.sync_aggregate
template sync_committee_bits(): auto = sync_aggregate.sync_committee_bits
let num_active_participants = countOnes(sync_committee_bits).uint64
if num_active_participants * 3 < static(sync_committee_bits.len * 2):
res = DidUpdateWithoutSupermajority
else:
res = DidUpdateWithoutFinality
store.best_valid_update.reset()
res
# https://github.com/ethereum/consensus-specs/blob/v1.4.0-alpha.3/specs/altair/light-client/sync-protocol.md#process_light_client_update
proc process_light_client_update*(
store: var ForkyLightClientStore,
update: SomeForkyLightClientUpdate,
current_slot: Slot,
cfg: RuntimeConfig,
genesis_validators_root: Eth2Digest): Result[void, VerifierError] =
? validate_light_client_update(
store, update, current_slot, cfg, genesis_validators_root)
var didProgress = false
# Update the best update in case we have to force-update to it
# if the timeout elapses
if store.best_valid_update.isNone or
is_better_update(update, store.best_valid_update.get):
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store.best_valid_update = Opt.some(update.toFull)
didProgress = true
# Track the maximum number of active participants in the committee signatures
template sync_aggregate(): auto = update.sync_aggregate
template sync_committee_bits(): auto = sync_aggregate.sync_committee_bits
let num_active_participants = countOnes(sync_committee_bits).uint64
if num_active_participants > store.current_max_active_participants:
store.current_max_active_participants = num_active_participants
# Update the optimistic header
if num_active_participants > get_safety_threshold(store) and
update.attested_header.beacon.slot > store.optimistic_header.beacon.slot:
store.optimistic_header = update.attested_header
didProgress = true
# Update finalized header
when update is SomeForkyLightClientUpdateWithFinality:
if num_active_participants * 3 >= static(sync_committee_bits.len * 2):
var improvesFinality =
update.finalized_header.beacon.slot > store.finalized_header.beacon.slot
when update is SomeForkyLightClientUpdateWithSyncCommittee:
if not improvesFinality and not store.is_next_sync_committee_known:
improvesFinality =
update.is_sync_committee_update and update.is_finality_update and
update.finalized_header.beacon.slot.sync_committee_period ==
update.attested_header.beacon.slot.sync_committee_period
if improvesFinality:
# Normal update through 2/3 threshold
if apply_light_client_update(store, update):
didProgress = true
store.best_valid_update.reset()
if not didProgress:
return err(VerifierError.Duplicate)
ok()