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Polish and fixes including fixed-size sync committees

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Justin 2020-11-18 09:19:32 +00:00 committed by GitHub
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35
specs/lightclient/beacon-chain.md
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@ -8,7 +8,6 @@
- [Introduction](#introduction)
- [Custom types](#custom-types)
- [Constants](#constants)
- [Configuration](#configuration)
- [Misc](#misc)
@ -21,7 +20,6 @@
- [New containers](#new-containers)
- [`SyncCommittee`](#synccommittee)
- [Helper functions](#helper-functions)
- [Misc](#misc-1)
- [Beacon state accessors](#beacon-state-accessors)
- [`get_sync_committee_indices`](#get_sync_committee_indices)
- [`get_sync_committee`](#get_sync_committee)
@ -37,11 +35,6 @@
This is a standalone beacon chain patch adding light client support via sync committees.
## Custom types
| Name | SSZ equivalent | Description |
| - | - | - |
## Constants
| Name | Value |
@ -54,7 +47,7 @@ This is a standalone beacon chain patch adding light client support via sync com
| Name | Value |
| - | - |
| `MAX_SYNC_COMMITTEE_SIZE` | `uint64(2**8)` (= 256) |
| `SYNC_COMMITTEE_SIZE` | `uint64(2**8)` (= 256) |
### Time parameters
@ -77,7 +70,7 @@ This is a standalone beacon chain patch adding light client support via sync com
```python
class BeaconBlockBody(phase0.BeaconBlockBody):
# Light client
sync_committee_bits: Bitlist[MAX_SYNC_COMMITTEE_SIZE]
sync_committee_bits: Bitvector[SYNC_COMMITTEE_SIZE]
sync_committee_signature: BLSSignature
```
@ -96,14 +89,12 @@ class BeaconState(phase0.BeaconState):
```python
class SyncCommittee(Container):
pubkeys: List[BLSPubkey, MAX_SYNC_COMMITTEE_SIZE]
pubkeys: Vector[BLSPubkey, SYNC_COMMITTEE_SIZE]
pubkeys_aggregate: BLSPubkey
```
## Helper functions
### Misc
### Beacon state accessors
#### `get_sync_committee_indices`
@ -114,18 +105,19 @@ def get_sync_committee_indices(state: BeaconState, epoch: Epoch) -> Sequence[Val
Return the sync committee indices for a given state and epoch.
"""
base_epoch = Epoch((max(epoch // EPOCHS_PER_SYNC_COMMITTEE_PERIOD, 1) - 1) * EPOCHS_PER_SYNC_COMMITTEE_PERIOD)
active_validator_count = uint64(len(get_active_validator_indices(state, base_epoch)))
sync_committee_size = min(active_validator_count, MAX_SYNC_COMMITTEE_SIZE)
active_validator_indices = get_active_validator_indices(state, base_epoch)
active_validator_count = uint64(len(active_validator_indices))
seed = get_seed(state, base_epoch, DOMAIN_SYNC_COMMITTEE)
i, output = 0, []
while i < active_validator_count and len(output) < sync_committee_size:
candidate_index = indices[compute_shuffled_index(uint64(i), active_validator_count, seed)]
i, sync_committee_indices = 0, []
while len(sync_committee_indices) < SYNC_COMMITTEE_SIZE:
shuffled_index = compute_shuffled_index(uint64(i % active_validator_count), active_validator_count, seed)
candidate_index = active_validator_indices[shuffled_index]
random_byte = hash(seed + uint_to_bytes(uint64(i // 32)))[i % 32]
effective_balance = state.validators[candidate_index].effective_balance
if effective_balance * MAX_RANDOM_BYTE >= MAX_EFFECTIVE_BALANCE * random_byte:
output.append(candidate_index)
sync_committee_indices.append(candidate_index)
i += 1
return output
return sync_committee_indices
```
#### `get_sync_committee`
@ -153,12 +145,9 @@ def process_block(state: BeaconState, block: BeaconBlock) -> None:
```python
def process_sync_committee(state: BeaconState, body: BeaconBlockBody) -> None:
# Verify sync committee bitfield length
committee_indices = get_sync_committee_indices(state, get_current_epoch(state))
assert len(body.sync_committee_bits) == len(committee_indices)
# Verify sync committee aggregate signature signing over the previous slot block root
previous_slot = max(state.slot, Slot(1)) - Slot(1)
committee_indices = get_sync_committee_indices(state, get_current_epoch(state))
participant_indices = [committee_indices[i] for i in range(len(committee_indices)) if body.sync_committee_bits[i]]
participant_pubkeys = [state.validators[participant_index].pubkey for participant_index in participant_indices]
domain = get_domain(state, DOMAIN_SYNC_COMMITTEE, compute_epoch_at_slot(previous_slot))