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vbuterin 2021-12-10 07:48:14 -06:00 committed by GitHub
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specs/altair/sync-protocol.md
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@ -53,7 +53,6 @@ uses sync committees introduced in [this beacon chain extension](./beacon-chain.
| - | - | - |
| `MIN_SYNC_COMMITTEE_PARTICIPANTS` | `1` | |
| `UPDATE_TIMEOUT` | `SLOTS_PER_EPOCH * EPOCHS_PER_SYNC_COMMITTEE_PERIOD` | ~27.3 hours |
| `SAFETY_THRESHOLD_PERIOD` | `SLOTS_PER_EPOCH * EPOCHS_PER_SYNC_COMMITTEE_PERIOD // 2` | ~13.6 hours |
## Containers
@ -70,8 +69,7 @@ class LightClientUpdate(Container):
finalized_header: BeaconBlockHeader
finality_branch: Vector[Bytes32, floorlog2(FINALIZED_ROOT_INDEX)]
# Sync committee aggregate signature
sync_committee_bits: Bitvector[SYNC_COMMITTEE_SIZE]
sync_committee_signature: BLSSignature
sync_committee_aggregate: SyncAggregate
# Fork version for the aggregate signature
fork_version: Version
```
@ -135,9 +133,16 @@ A light client maintains its state in a `store` object of type `LightClientStore
```python
def process_slot_for_light_client_store(store: LightClientStore, current_slot: Slot) -> None:
if current_slot % SAFETY_THRESHOLD_PERIOD == 0:
if current_slot % UPDATE_TIMEOUT == 0:
store.previous_max_active_participants = store.current_max_active_participants
store.current_max_active_participants = 0
if (
current_slot > store.finalized_header.slot + UPDATE_TIMEOUT
and store.best_valid_update is not None
):
# Forced best update when the update timeout has elapsed
apply_light_client_update(store, store.best_valid_update)
store.best_valid_update = None
```
#### `validate_light_client_update`
@ -157,7 +162,8 @@ def validate_light_client_update(store: LightClientStore,
update_period = compute_epoch_at_slot(active_header.slot) // EPOCHS_PER_SYNC_COMMITTEE_PERIOD
assert update_period in (finalized_period, finalized_period + 1)
# Verify update header root is the finalized root of the finality header, if specified
# Verify that the `finalized_header`, if present, actually is the finalized header saved in the
# state of the `attested header`
if update.finalized_header == BeaconBlockHeader():
assert update.finality_branch == [Bytes32() for _ in range(floorlog2(FINALIZED_ROOT_INDEX))]
else:
@ -182,15 +188,17 @@ def validate_light_client_update(store: LightClientStore,
index=get_subtree_index(NEXT_SYNC_COMMITTEE_INDEX),
root=active_header.state_root,
)
sync_aggregate = update.sync_committee_aggregate
# Verify sync committee has sufficient participants
assert sum(update.sync_committee_bits) >= MIN_SYNC_COMMITTEE_PARTICIPANTS
assert sum(sync_aggregate.sync_committee_bits) >= MIN_SYNC_COMMITTEE_PARTICIPANTS
# Verify sync committee aggregate signature
participant_pubkeys = [pubkey for (bit, pubkey) in zip(update.sync_committee_bits, sync_committee.pubkeys) if bit]
participant_pubkeys = [pubkey for (bit, pubkey) in zip(sync_aggregate.sync_committee_bits, sync_committee.pubkeys) if bit]
domain = compute_domain(DOMAIN_SYNC_COMMITTEE, update.fork_version, genesis_validators_root)
signing_root = compute_signing_root(update.attested_header, domain)
assert bls.FastAggregateVerify(participant_pubkeys, signing_root, update.sync_committee_signature)
assert bls.FastAggregateVerify(participant_pubkeys, signing_root, sync_aggregate.sync_committee_signature)
```
#### `apply_light_client_update`
@ -244,11 +252,4 @@ def process_light_client_update(store: LightClientStore,
# Normal update through 2/3 threshold
apply_light_client_update(store, update)
store.best_valid_update = None
elif (
current_slot > store.finalized_header.slot + UPDATE_TIMEOUT
and store.best_valid_update is not None
):
# Forced best update when the update timeout has elapsed
apply_light_client_update(store, store.best_valid_update)
store.best_valid_update = None
```