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Optimized sync committee signature verification #4687

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jtraglia merged 3 commits into from
Oct 29, 2025
Merged

Optimized sync committee signature verification #4687

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4d5e153
optimized sync committee signature verification to leverage precomput…
AbolareRoheemah Oct 22, 2025
1aa0d9f
minor comment fix & documented eth_fast_aggregate_verify's usability …
AbolareRoheemah Oct 23, 2025
3f5888d
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jtraglia Oct 23, 2025
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30 changes: 27 additions & 3 deletions specs/altair/beacon-chain.md
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Original file line number Diff line number Diff line change
Expand Up @@ -571,12 +571,36 @@ def add_validator_to_registry(
def process_sync_aggregate(state: BeaconState, sync_aggregate: SyncAggregate) -> None:
# Verify sync committee aggregate signature signing over the previous slot block root
committee_pubkeys = state.current_sync_committee.pubkeys
participant_pubkeys = [
pubkey for pubkey, bit in zip(committee_pubkeys, sync_aggregate.sync_committee_bits) if bit
]
committee_bits = sync_aggregate.sync_committee_bits
if sum(committee_bits) == SYNC_COMMITTEE_SIZE:
# All members participated - use precomputed aggregate key
participant_pubkeys = [state.current_sync_committee.aggregate_pubkey]
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elif sum(committee_bits) > SYNC_COMMITTEE_SIZE // 2:
# More than half participated - subtract non-participant keys.
# First determine nonparticipating members
non_participant_pubkeys = [
pubkey for pubkey, bit in zip(committee_pubkeys, committee_bits) if not bit
]
# Compute aggregate of non-participants
non_participant_aggregate = eth_aggregate_pubkeys(non_participant_pubkeys)
# Subtract non-participants from the full aggregate
# This is equivalent to: aggregate_pubkey + (-non_participant_aggregate)
participant_pubkey = bls.add(
bls.bytes48_to_G1(state.current_sync_committee.aggregate_pubkey),
bls.neg(bls.bytes48_to_G1(non_participant_aggregate)),
)
participant_pubkeys = [BLSPubkey(bls.G1_to_bytes48(participant_pubkey))]
else:
# Less than half participated - aggregate participant keys
participant_pubkeys = [
pubkey
for pubkey, bit in zip(committee_pubkeys, sync_aggregate.sync_committee_bits)
if bit
]
previous_slot = max(state.slot, Slot(1)) - Slot(1)
domain = get_domain(state, DOMAIN_SYNC_COMMITTEE, compute_epoch_at_slot(previous_slot))
signing_root = compute_signing_root(get_block_root_at_slot(state, previous_slot), domain)
# Note: eth_fast_aggregate_verify works with a singleton list containing an aggregated key
assert eth_fast_aggregate_verify(
participant_pubkeys, signing_root, sync_aggregate.sync_committee_signature
)
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