Ethereum 2.0 Light Client Support
Table of contents
Introduction
This is a standalone beacon chain patch adding light client support via sync committees.
Constants
| Name |
Value |
BASE_REWARDS_PER_EPOCH |
uint64(5) |
Configuration
Misc
| Name |
Value |
SYNC_COMMITTEE_SIZE |
uint64(2**8) (= 256) |
Time parameters
| Name |
Value |
Unit |
Duration |
EPOCHS_PER_SYNC_COMMITTEE_PERIOD |
Epoch(2**8) (= 256) |
epochs |
~27 hours |
Domain types
| Name |
Value |
DOMAIN_SYNC_COMMITTEE |
DomainType('0x07000000') |
Containers
Extended containers
BeaconBlockBody
class BeaconBlockBody(phase0.BeaconBlockBody):
# Light client
sync_committee_bits: Bitvector[SYNC_COMMITTEE_SIZE]
sync_committee_signature: BLSSignature
BeaconState
class BeaconState(phase0.BeaconState):
# Light client
current_sync_committee: SyncCommittee
next_sync_committee: SyncCommittee
New containers
SyncCommittee
class SyncCommittee(Container):
pubkeys: Vector[BLSPubkey, SYNC_COMMITTEE_SIZE]
pubkeys_aggregate: BLSPubkey
Helper functions
Beacon state accessors
get_sync_committee_indices
def get_sync_committee_indices(state: BeaconState, epoch: Epoch) -> Sequence[ValidatorIndex]:
"""
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_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, 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:
sync_committee_indices.append(candidate_index)
i += 1
return sync_committee_indices
get_sync_committee
def get_sync_committee(state: BeaconState, epoch: Epoch) -> SyncCommittee:
"""
Return the sync committee for a given state and epoch.
"""
indices = get_sync_committee_indices(state, epoch)
validators = [state.validators[index] for index in indices]
pubkeys = [validator.pubkey for validator in validators]
return SyncCommittee(pubkeys, bls.AggregatePKs(pubkeys))
Block processing
def process_block(state: BeaconState, block: BeaconBlock) -> None:
phase0.process_block(state, block)
process_sync_committee(state, block.body)
Sync committee processing
def process_sync_committee(state: BeaconState, body: BeaconBlockBody) -> None:
# 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))
signing_root = compute_signing_root(get_block_root_at_slot(state, previous_slot), domain)
assert bls.FastAggregateVerify(participant_pubkeys, signing_root, body.sync_committee_signature)
# Reward sync committee participants
participant_rewards = Gwei(0)
active_validator_count = uint64(len(get_active_validator_indices(state, get_current_epoch(state))))
for participant_index in participant_indices:
base_reward = get_base_reward(state, participant_index)
reward = Gwei(base_reward * active_validator_count // len(committee_indices) // SLOTS_PER_EPOCH)
increase_balance(state, participant_index, reward)
participant_rewards += reward
# Reward beacon proposer
increase_balance(state, get_beacon_proposer_index(state), Gwei(participant_rewards // PROPOSER_REWARD_QUOTIENT))
Epoch processing
Final updates
def process_final_updates(state: BeaconState) -> None:
phase0.process_final_updates(state)
next_epoch = get_current_epoch(state) + Epoch(1)
if next_epoch % EPOCHS_PER_SYNC_COMMITTEE_PERIOD == 0:
state.current_sync_committee = state.next_sync_committee
state.next_sync_committee = get_sync_committee(state, next_epoch + EPOCHS_PER_SYNC_COMMITTEE_PERIOD)