import stew/[bitops2, objects], datatypes/altair, helpers # https://github.com/ethereum/consensus-specs/blob/v1.1.8/specs/altair/sync-protocol.md#get_active_header func get_active_header(update: LightClientUpdate): BeaconBlockHeader = # The "active header" is the header that the update is trying to convince # us to accept. If a finalized header is present, it's the finalized # header, otherwise it's the attested header if not update.finalized_header.isZeroMemory: update.finalized_header else: update.attested_header # https://github.com/ethereum/consensus-specs/blob/v1.1.8/specs/altair/sync-protocol.md#validate_light_client_update proc validate_light_client_update*(store: LightClientStore, update: LightClientUpdate, current_slot: Slot, genesis_validators_root: Eth2Digest): bool = # Verify update slot is larger than slot of current best finalized header let active_header = get_active_header(update) if not (current_slot >= active_header.slot and active_header.slot > store.finalized_header.slot): return false # Verify update does not skip a sync committee period let finalized_period = sync_committee_period(store.finalized_header.slot) update_period = sync_committee_period(active_header.slot) if update_period notin [finalized_period, finalized_period + 1]: return false # Verify that the `finalized_header`, if present, actually is the finalized # header saved in the state of the `attested header` if update.finalized_header.isZeroMemory: if not update.finality_branch.isZeroMemory: return false else: if not is_valid_merkle_branch(hash_tree_root(update.finalized_header), update.finality_branch, log2trunc(FINALIZED_ROOT_INDEX), get_subtree_index(FINALIZED_ROOT_INDEX), update.attested_header.state_root): return false # Verify update next sync committee if the update period incremented # TODO: Use a view type instead of `unsafeAddr` let sync_committee = if update_period == finalized_period: if not update.next_sync_committee_branch.isZeroMemory: return false unsafeAddr store.current_sync_committee else: if not is_valid_merkle_branch(hash_tree_root(update.next_sync_committee), update.next_sync_committee_branch, log2trunc(NEXT_SYNC_COMMITTEE_INDEX), get_subtree_index(NEXT_SYNC_COMMITTEE_INDEX), active_header.state_root): return false unsafeAddr store.next_sync_committee template sync_aggregate(): auto = update.sync_committee_aggregate let sync_committee_participants_count = countOnes(sync_aggregate.sync_committee_bits) # Verify sync committee has sufficient participants if sync_committee_participants_count < MIN_SYNC_COMMITTEE_PARTICIPANTS: return false # Verify sync committee aggregate signature # participant_pubkeys = [pubkey for (bit, pubkey) in zip(sync_aggregate.sync_committee_bits, sync_committee.pubkeys) if bit] var participant_pubkeys = newSeqOfCap[ValidatorPubKey](sync_committee_participants_count) for idx, bit in sync_aggregate.sync_committee_bits: if bit: participant_pubkeys.add(sync_committee.pubkeys[idx]) let domain = compute_domain( DOMAIN_SYNC_COMMITTEE, update.fork_version, genesis_validators_root) let signing_root = compute_signing_root(update.attested_header, domain) blsFastAggregateVerify( participant_pubkeys, signing_root.data, sync_aggregate.sync_committee_signature) # https://github.com/ethereum/consensus-specs/blob/v1.1.8/specs/altair/sync-protocol.md#apply_light_client_update func apply_light_client_update( store: var LightClientStore, update: LightClientUpdate) = let active_header = get_active_header(update) finalized_period = sync_committee_period(store.finalized_header.slot) update_period = sync_committee_period(active_header.slot) if update_period == finalized_period + 1: store.current_sync_committee = store.next_sync_committee store.next_sync_committee = update.next_sync_committee store.finalized_header = active_header # https://github.com/ethereum/consensus-specs/blob/v1.1.8/specs/altair/sync-protocol.md#get_safety_threshold func get_safety_threshold(store: LightClientStore): uint64 = max( store.previous_max_active_participants, store.current_max_active_participants ) div 2 # https://github.com/ethereum/consensus-specs/blob/v1.1.8/specs/altair/sync-protocol.md#process_light_client_update proc process_light_client_update*(store: var LightClientStore, update: LightClientUpdate, current_slot: Slot, genesis_validators_root: Eth2Digest): bool = if not validate_light_client_update( store, update, current_slot, genesis_validators_root): return false let sync_committee_bits = update.sync_committee_aggregate.sync_committee_bits sum_sync_committee_bits = countOnes(sync_committee_bits) # Update the best update in case we have to force-update to it if the # timeout elapses if store.best_valid_update.isNone or sum_sync_committee_bits > countOnes( store.best_valid_update.get.sync_committee_aggregate.sync_committee_bits): store.best_valid_update = some(update) # Track the maximum number of active participants in the committee signatures store.current_max_active_participants = max( store.current_max_active_participants, sum_sync_committee_bits.uint64, ) # Update the optimistic header if sum_sync_committee_bits.uint64 > get_safety_threshold(store) and update.attested_header.slot > store.optimistic_header.slot: store.optimistic_header = update.attested_header # Update finalized header if sum_sync_committee_bits * 3 >= len(sync_committee_bits) * 2 and not update.finalized_header.isZeroMemory: # Normal update through 2/3 threshold apply_light_client_update(store, update) store.best_valid_update = none(LightClientUpdate) true