# Ethereum 2.0 Altair Beacon chain changes ## Table of contents - [Introduction](#introduction) - [Custom types](#custom-types) - [Constants](#constants) - [Participation flag indices](#participation-flag-indices) - [Participation flag fractions](#participation-flag-fractions) - [Misc](#misc) - [Configuration](#configuration) - [Updated penalty values](#updated-penalty-values) - [Misc](#misc-1) - [Time parameters](#time-parameters) - [Domain types](#domain-types) - [Containers](#containers) - [Modified containers](#modified-containers) - [`BeaconBlockBody`](#beaconblockbody) - [`BeaconState`](#beaconstate) - [New containers](#new-containers) - [`SyncCommittee`](#synccommittee) - [Helper functions](#helper-functions) - [`Predicates`](#predicates) - [`eth2_fast_aggregate_verify`](#eth2_fast_aggregate_verify) - [Misc](#misc-2) - [`get_flag_indices_and_numerators`](#get_flag_indices_and_numerators) - [`add_flag`](#add_flag) - [`has_flag`](#has_flag) - [Beacon state accessors](#beacon-state-accessors) - [`get_sync_committee_indices`](#get_sync_committee_indices) - [`get_sync_committee`](#get_sync_committee) - [`get_base_reward`](#get_base_reward) - [`get_unslashed_participating_indices`](#get_unslashed_participating_indices) - [`get_flag_index_deltas`](#get_flag_index_deltas) - [Modified `get_inactivity_penalty_deltas`](#modified-get_inactivity_penalty_deltas) - [Beacon state mutators](#beacon-state-mutators) - [Modified `slash_validator`](#modified-slash_validator) - [Block processing](#block-processing) - [Modified `process_attestation`](#modified-process_attestation) - [Modified `process_deposit`](#modified-process_deposit) - [Sync committee processing](#sync-committee-processing) - [Epoch processing](#epoch-processing) - [Justification and finalization](#justification-and-finalization) - [Inactivity scores](#inactivity-scores) - [Rewards and penalties](#rewards-and-penalties) - [Slashings](#slashings) - [Participation flags updates](#participation-flags-updates) - [Sync committee updates](#sync-committee-updates) ## Introduction Altair is the first beacon chain hard fork. Its main features are: * sync committees to support light clients * incentive accounting reforms to reduce spec complexity * penalty parameter updates to move them to their planned maximally punitive configuration ## Custom types | Name | SSZ equivalent | Description | | - | - | - | | `ParticipationFlags` | `uint8` | a succinct representation of 8 boolean participation flags | ## Constants ### Participation flag indices | Name | Value | | - | - | | `TIMELY_HEAD_FLAG_INDEX` | `0` | | `TIMELY_SOURCE_FLAG_INDEX` | `1` | | `TIMELY_TARGET_FLAG_INDEX` | `2` | ### Participation flag fractions | Name | Value | | - | - | | `TIMELY_HEAD_FLAG_NUMERATOR` | `12` | | `TIMELY_SOURCE_FLAG_NUMERATOR` | `12` | | `TIMELY_TARGET_FLAG_NUMERATOR` | `32` | | `FLAG_DENOMINATOR` | `64` | **Note**: The sum of the participatition flag fractions (7/8) plus the proposer reward fraction (1/8) equals 1. ### Misc | Name | Value | | - | - | | `G2_POINT_AT_INFINITY` | `BLSSignature(b'\xc0' + b'\x00' * 95)` | ## Configuration ### Updated penalty values This patch updates a few configuration values to move penalty parameters toward their final, maxmium security values. *Note*: The spec does *not* override previous configuration values but instead creates new values and replaces usage throughout. | Name | Value | | - | - | | `ALTAIR_INACTIVITY_PENALTY_QUOTIENT` | `uint64(3 * 2**24)` (= 50,331,648) | | `ALTAIR_MIN_SLASHING_PENALTY_QUOTIENT` | `uint64(2**6)` (= 64) | | `ALTAIR_PROPORTIONAL_SLASHING_MULTIPLIER` | `uint64(2)` | ### Misc | Name | Value | | - | - | | `SYNC_COMMITTEE_SIZE` | `uint64(2**10)` (= 1,024) | | `SYNC_SUBCOMMITTEE_SIZE` | `uint64(2**6)` (= 64) | | `INACTIVITY_SCORE_BIAS` | `uint64(4)` | ### 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 ### Modified containers #### `BeaconBlockBody` ```python class BeaconBlockBody(Container): randao_reveal: BLSSignature eth1_data: Eth1Data # Eth1 data vote graffiti: Bytes32 # Arbitrary data # Operations proposer_slashings: List[ProposerSlashing, MAX_PROPOSER_SLASHINGS] attester_slashings: List[AttesterSlashing, MAX_ATTESTER_SLASHINGS] attestations: List[Attestation, MAX_ATTESTATIONS] deposits: List[Deposit, MAX_DEPOSITS] voluntary_exits: List[SignedVoluntaryExit, MAX_VOLUNTARY_EXITS] # Sync committee aggregate signature sync_committee_bits: Bitvector[SYNC_COMMITTEE_SIZE] # [New in Altair] sync_committee_signature: BLSSignature # [New in Altair] ``` #### `BeaconState` ```python class BeaconState(Container): # Versioning genesis_time: uint64 genesis_validators_root: Root slot: Slot fork: Fork # History latest_block_header: BeaconBlockHeader block_roots: Vector[Root, SLOTS_PER_HISTORICAL_ROOT] state_roots: Vector[Root, SLOTS_PER_HISTORICAL_ROOT] historical_roots: List[Root, HISTORICAL_ROOTS_LIMIT] # Eth1 eth1_data: Eth1Data eth1_data_votes: List[Eth1Data, EPOCHS_PER_ETH1_VOTING_PERIOD * SLOTS_PER_EPOCH] eth1_deposit_index: uint64 # Registry validators: List[Validator, VALIDATOR_REGISTRY_LIMIT] balances: List[Gwei, VALIDATOR_REGISTRY_LIMIT] # Randomness randao_mixes: Vector[Bytes32, EPOCHS_PER_HISTORICAL_VECTOR] # Slashings slashings: Vector[Gwei, EPOCHS_PER_SLASHINGS_VECTOR] # Per-epoch sums of slashed effective balances # Participation previous_epoch_participation: List[ParticipationFlags, VALIDATOR_REGISTRY_LIMIT] # [Modified in Altair] current_epoch_participation: List[ParticipationFlags, VALIDATOR_REGISTRY_LIMIT] # [Modified in Altair] # Finality justification_bits: Bitvector[JUSTIFICATION_BITS_LENGTH] # Bit set for every recent justified epoch previous_justified_checkpoint: Checkpoint current_justified_checkpoint: Checkpoint finalized_checkpoint: Checkpoint # Inactivity inactivity_scores: List[uint64, VALIDATOR_REGISTRY_LIMIT] # [New in Altair] # Sync current_sync_committee: SyncCommittee # [New in Altair] next_sync_committee: SyncCommittee # [New in Altair] ``` ### New containers #### `SyncCommittee` ```python class SyncCommittee(Container): pubkeys: Vector[BLSPubkey, SYNC_COMMITTEE_SIZE] pubkey_aggregates: Vector[BLSPubkey, SYNC_COMMITTEE_SIZE // SYNC_SUBCOMMITTEE_SIZE] ``` ## Helper functions ### `Predicates` #### `eth2_fast_aggregate_verify` ```python def eth2_fast_aggregate_verify(pubkeys: Sequence[BLSPubkey], message: Bytes32, signature: BLSSignature) -> bool: """ Wrapper to ``bls.FastAggregateVerify`` accepting the ``G2_POINT_AT_INFINITY`` signature when ``pubkeys`` is empty. """ if len(pubkeys) == 0 and signature == G2_POINT_AT_INFINITY: return True return bls.FastAggregateVerify(pubkeys, message, signature) ``` ### Misc #### `get_flag_indices_and_numerators` ```python def get_flag_indices_and_numerators() -> Sequence[Tuple[int, int]]: return ( (TIMELY_HEAD_FLAG_INDEX, TIMELY_HEAD_FLAG_NUMERATOR), (TIMELY_SOURCE_FLAG_INDEX, TIMELY_SOURCE_FLAG_NUMERATOR), (TIMELY_TARGET_FLAG_INDEX, TIMELY_TARGET_FLAG_NUMERATOR), ) ``` #### `add_flag` ```python def add_flag(flags: ParticipationFlags, flag_index: int) -> ParticipationFlags: flag = ParticipationFlags(2**flag_index) return flags | flag ``` #### `has_flag` ```python def has_flag(flags: ParticipationFlags, flag_index: int) -> bool: flag = ParticipationFlags(2**flag_index) return flags & flag == flag ``` ### Beacon state accessors #### `get_sync_committee_indices` ```python def get_sync_committee_indices(state: BeaconState, epoch: Epoch) -> Sequence[ValidatorIndex]: """ Return the sequence of sync committee indices (which may include duplicate indices) for a given state and epoch. """ MAX_RANDOM_BYTE = 2**8 - 1 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 = 0 sync_committee_indices: List[ValidatorIndex] = [] 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: # Sample with replacement sync_committee_indices.append(candidate_index) i += 1 return sync_committee_indices ``` #### `get_sync_committee` ```python 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) pubkeys = [state.validators[index].pubkey for index in indices] subcommitees = [pubkeys[i:i + SYNC_SUBCOMMITTEE_SIZE] for i in range(0, len(pubkeys), SYNC_SUBCOMMITTEE_SIZE)] pubkey_aggregates = [bls.AggregatePKs(subcommitee) for subcommitee in subcommitees] return SyncCommittee(pubkeys=pubkeys, pubkey_aggregates=pubkey_aggregates) ``` #### `get_base_reward` *Note*: The function `get_base_reward` is modified with the removal of `BASE_REWARDS_PER_EPOCH`. ```python def get_base_reward(state: BeaconState, index: ValidatorIndex) -> Gwei: total_balance = get_total_active_balance(state) effective_balance = state.validators[index].effective_balance return Gwei(effective_balance * BASE_REWARD_FACTOR // integer_squareroot(total_balance)) ``` #### `get_unslashed_participating_indices` ```python def get_unslashed_participating_indices(state: BeaconState, flag_index: int, epoch: Epoch) -> Set[ValidatorIndex]: """ Return the active and unslashed validator indices for the given epoch and flag index. """ assert epoch in (get_previous_epoch(state), get_current_epoch(state)) if epoch == get_current_epoch(state): epoch_participation = state.current_epoch_participation else: epoch_participation = state.previous_epoch_participation active_validator_indices = get_active_validator_indices(state, epoch) participating_indices = [i for i in active_validator_indices if has_flag(epoch_participation[i], flag_index)] return set(filter(lambda index: not state.validators[index].slashed, participating_indices)) ``` #### `get_flag_index_deltas` ```python def get_flag_index_deltas(state: BeaconState, flag_index: int, numerator: uint64) -> Tuple[Sequence[Gwei], Sequence[Gwei]]: """ Return the deltas for a given flag index by scanning through the participation flags. """ rewards = [Gwei(0)] * len(state.validators) penalties = [Gwei(0)] * len(state.validators) unslashed_participating_indices = get_unslashed_participating_indices(state, flag_index, get_previous_epoch(state)) increment = EFFECTIVE_BALANCE_INCREMENT # Factored out from balances to avoid uint64 overflow unslashed_participating_increments = get_total_balance(state, unslashed_participating_indices) // increment active_increments = get_total_active_balance(state) // increment for index in get_eligible_validator_indices(state): base_reward = get_base_reward(state, index) if index in unslashed_participating_indices: if is_in_inactivity_leak(state): # This flag reward cancels the inactivity penalty corresponding to the flag index rewards[index] += Gwei(base_reward * numerator // FLAG_DENOMINATOR) else: reward_numerator = base_reward * numerator * unslashed_participating_increments rewards[index] += Gwei(reward_numerator // (active_increments * FLAG_DENOMINATOR)) else: penalties[index] += Gwei(base_reward * numerator // FLAG_DENOMINATOR) return rewards, penalties ``` #### Modified `get_inactivity_penalty_deltas` *Note*: The function `get_inactivity_penalty_deltas` is modified in the selection of matching target indices and the removal of `BASE_REWARDS_PER_EPOCH`. ```python def get_inactivity_penalty_deltas(state: BeaconState) -> Tuple[Sequence[Gwei], Sequence[Gwei]]: """ Return the inactivity penalty deltas by considering timely target participation flags and inactivity scores. """ rewards = [Gwei(0) for _ in range(len(state.validators))] penalties = [Gwei(0) for _ in range(len(state.validators))] if is_in_inactivity_leak(state): previous_epoch = get_previous_epoch(state) matching_target_indices = get_unslashed_participating_indices(state, TIMELY_TARGET_FLAG_INDEX, previous_epoch) for index in get_eligible_validator_indices(state): for (_, numerator) in get_flag_indices_and_numerators(): # This inactivity penalty cancels the flag reward corresponding to the flag index penalties[index] += Gwei(get_base_reward(state, index) * numerator // FLAG_DENOMINATOR) if index not in matching_target_indices: penalty_numerator = state.validators[index].effective_balance * state.inactivity_scores[index] penalty_denominator = INACTIVITY_SCORE_BIAS * ALTAIR_INACTIVITY_PENALTY_QUOTIENT penalties[index] += Gwei(penalty_numerator // penalty_denominator) return rewards, penalties ``` ### Beacon state mutators #### Modified `slash_validator` *Note*: The function `slash_validator` is modified to use `ALTAIR_MIN_SLASHING_PENALTY_QUOTIENT`. ```python def slash_validator(state: BeaconState, slashed_index: ValidatorIndex, whistleblower_index: ValidatorIndex=None) -> None: """ Slash the validator with index ``slashed_index``. """ epoch = get_current_epoch(state) initiate_validator_exit(state, slashed_index) validator = state.validators[slashed_index] validator.slashed = True validator.withdrawable_epoch = max(validator.withdrawable_epoch, Epoch(epoch + EPOCHS_PER_SLASHINGS_VECTOR)) state.slashings[epoch % EPOCHS_PER_SLASHINGS_VECTOR] += validator.effective_balance decrease_balance(state, slashed_index, validator.effective_balance // ALTAIR_MIN_SLASHING_PENALTY_QUOTIENT) # Apply proposer and whistleblower rewards proposer_index = get_beacon_proposer_index(state) if whistleblower_index is None: whistleblower_index = proposer_index whistleblower_reward = Gwei(validator.effective_balance // WHISTLEBLOWER_REWARD_QUOTIENT) proposer_reward = Gwei(whistleblower_reward // PROPOSER_REWARD_QUOTIENT) increase_balance(state, proposer_index, proposer_reward) increase_balance(state, whistleblower_index, Gwei(whistleblower_reward - proposer_reward)) ``` ### Block processing ```python def process_block(state: BeaconState, block: BeaconBlock) -> None: process_block_header(state, block) process_randao(state, block.body) process_eth1_data(state, block.body) process_operations(state, block.body) # [Modified in Altair] process_sync_committee(state, block.body) # [New in Altair] ``` #### Modified `process_attestation` *Note*: The function `process_attestation` is modified to do incentive accounting with epoch participation flags. ```python def process_attestation(state: BeaconState, attestation: Attestation) -> None: data = attestation.data assert data.target.epoch in (get_previous_epoch(state), get_current_epoch(state)) assert data.target.epoch == compute_epoch_at_slot(data.slot) assert data.slot + MIN_ATTESTATION_INCLUSION_DELAY <= state.slot <= data.slot + SLOTS_PER_EPOCH assert data.index < get_committee_count_per_slot(state, data.target.epoch) committee = get_beacon_committee(state, data.slot, data.index) assert len(attestation.aggregation_bits) == len(committee) if data.target.epoch == get_current_epoch(state): epoch_participation = state.current_epoch_participation justified_checkpoint = state.current_justified_checkpoint else: epoch_participation = state.previous_epoch_participation justified_checkpoint = state.previous_justified_checkpoint # Matching roots is_matching_head = data.beacon_block_root == get_block_root_at_slot(state, data.slot) is_matching_source = data.source == justified_checkpoint is_matching_target = data.target.root == get_block_root(state, data.target.epoch) assert is_matching_source # Verify signature assert is_valid_indexed_attestation(state, get_indexed_attestation(state, attestation)) # Participation flag indices participation_flag_indices = [] if is_matching_head and is_matching_target and state.slot <= data.slot + MIN_ATTESTATION_INCLUSION_DELAY: participation_flag_indices.append(TIMELY_HEAD_FLAG_INDEX) if is_matching_source and state.slot <= data.slot + integer_squareroot(SLOTS_PER_EPOCH): participation_flag_indices.append(TIMELY_SOURCE_FLAG_INDEX) if is_matching_target and state.slot <= data.slot + SLOTS_PER_EPOCH: participation_flag_indices.append(TIMELY_TARGET_FLAG_INDEX) # Update epoch participation flags proposer_reward_numerator = 0 for index in get_attesting_indices(state, data, attestation.aggregation_bits): for flag_index, flag_numerator in get_flag_indices_and_numerators(): if flag_index in participation_flag_indices and not has_flag(epoch_participation[index], flag_index): epoch_participation[index] = add_flag(epoch_participation[index], flag_index) proposer_reward_numerator += get_base_reward(state, index) * flag_numerator # Reward proposer proposer_reward = Gwei(proposer_reward_numerator // (FLAG_DENOMINATOR * PROPOSER_REWARD_QUOTIENT)) increase_balance(state, get_beacon_proposer_index(state), proposer_reward) ``` #### Modified `process_deposit` *Note*: The function `process_deposit` is modified to initialize `inactivity_scores`, `previous_epoch_participation`, `current_epoch_participation`. ```python def process_deposit(state: BeaconState, deposit: Deposit) -> None: # Verify the Merkle branch assert is_valid_merkle_branch( leaf=hash_tree_root(deposit.data), branch=deposit.proof, depth=DEPOSIT_CONTRACT_TREE_DEPTH + 1, # Add 1 for the List length mix-in index=state.eth1_deposit_index, root=state.eth1_data.deposit_root, ) # Deposits must be processed in order state.eth1_deposit_index += 1 pubkey = deposit.data.pubkey amount = deposit.data.amount validator_pubkeys = [validator.pubkey for validator in state.validators] if pubkey not in validator_pubkeys: # Verify the deposit signature (proof of possession) which is not checked by the deposit contract deposit_message = DepositMessage( pubkey=deposit.data.pubkey, withdrawal_credentials=deposit.data.withdrawal_credentials, amount=deposit.data.amount, ) domain = compute_domain(DOMAIN_DEPOSIT) # Fork-agnostic domain since deposits are valid across forks signing_root = compute_signing_root(deposit_message, domain) # Initialize validator if the deposit signature is valid if bls.Verify(pubkey, signing_root, deposit.data.signature): state.validators.append(get_validator_from_deposit(state, deposit)) state.balances.append(amount) state.previous_epoch_participation.append(ParticipationFlags(0b0000_0000)) state.current_epoch_participation.append(ParticipationFlags(0b0000_0000)) state.inactivity_scores.append(0) else: # Increase balance by deposit amount index = ValidatorIndex(validator_pubkeys.index(pubkey)) increase_balance(state, index, amount) ``` #### Sync committee processing ```python def process_sync_committee(state: BeaconState, body: BeaconBlockBody) -> None: # Verify sync committee aggregate signature signing over the previous slot block root previous_slot = Slot(max(int(state.slot), 1) - 1) committee_indices = get_sync_committee_indices(state, get_current_epoch(state)) participant_indices = [index for index, bit in zip(committee_indices, body.sync_committee_bits) if bit] committee_pubkeys = state.current_sync_committee.pubkeys participant_pubkeys = [pubkey for pubkey, bit in zip(committee_pubkeys, body.sync_committee_bits) if bit] 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 eth2_fast_aggregate_verify(participant_pubkeys, signing_root, body.sync_committee_signature) # Reward sync committee participants proposer_rewards = Gwei(0) active_validator_count = uint64(len(get_active_validator_indices(state, get_current_epoch(state)))) for participant_index in participant_indices: proposer_reward = get_proposer_reward(state, participant_index) proposer_rewards += proposer_reward base_reward = get_base_reward(state, participant_index) max_participant_reward = base_reward - proposer_reward reward = Gwei(max_participant_reward * active_validator_count // (len(committee_indices) * SLOTS_PER_EPOCH)) increase_balance(state, participant_index, reward) # Reward beacon proposer increase_balance(state, get_beacon_proposer_index(state), proposer_rewards) ``` ### Epoch processing ```python def process_epoch(state: BeaconState) -> None: process_justification_and_finalization(state) # [Modified in Altair] process_inactivity_updates(state) # [New in Altair] process_rewards_and_penalties(state) # [Modified in Altair] process_registry_updates(state) process_slashings(state) # [Modified in Altair] process_eth1_data_reset(state) process_effective_balance_updates(state) process_slashings_reset(state) process_randao_mixes_reset(state) process_historical_roots_update(state) process_participation_flag_updates(state) # [New in Altair] process_sync_committee_updates(state) # [New in Altair] ``` #### Justification and finalization *Note*: The function `process_justification_and_finalization` is modified with `matching_target_attestations` replaced by `matching_target_indices`. ```python def process_justification_and_finalization(state: BeaconState) -> None: # Initial FFG checkpoint values have a `0x00` stub for `root`. # Skip FFG updates in the first two epochs to avoid corner cases that might result in modifying this stub. if get_current_epoch(state) <= GENESIS_EPOCH + 1: return previous_epoch = get_previous_epoch(state) current_epoch = get_current_epoch(state) old_previous_justified_checkpoint = state.previous_justified_checkpoint old_current_justified_checkpoint = state.current_justified_checkpoint # Process justifications state.previous_justified_checkpoint = state.current_justified_checkpoint state.justification_bits[1:] = state.justification_bits[:JUSTIFICATION_BITS_LENGTH - 1] state.justification_bits[0] = 0b0 matching_target_indices = get_unslashed_participating_indices(state, TIMELY_TARGET_FLAG_INDEX, previous_epoch) if get_total_balance(state, matching_target_indices) * 3 >= get_total_active_balance(state) * 2: state.current_justified_checkpoint = Checkpoint(epoch=previous_epoch, root=get_block_root(state, previous_epoch)) state.justification_bits[1] = 0b1 matching_target_indices = get_unslashed_participating_indices(state, TIMELY_TARGET_FLAG_INDEX, current_epoch) if get_total_balance(state, matching_target_indices) * 3 >= get_total_active_balance(state) * 2: state.current_justified_checkpoint = Checkpoint(epoch=current_epoch, root=get_block_root(state, current_epoch)) state.justification_bits[0] = 0b1 # Process finalizations bits = state.justification_bits # The 2nd/3rd/4th most recent epochs are justified, the 2nd using the 4th as source if all(bits[1:4]) and old_previous_justified_checkpoint.epoch + 3 == current_epoch: state.finalized_checkpoint = old_previous_justified_checkpoint # The 2nd/3rd most recent epochs are justified, the 2nd using the 3rd as source if all(bits[1:3]) and old_previous_justified_checkpoint.epoch + 2 == current_epoch: state.finalized_checkpoint = old_previous_justified_checkpoint # The 1st/2nd/3rd most recent epochs are justified, the 1st using the 3rd as source if all(bits[0:3]) and old_current_justified_checkpoint.epoch + 2 == current_epoch: state.finalized_checkpoint = old_current_justified_checkpoint # The 1st/2nd most recent epochs are justified, the 1st using the 2nd as source if all(bits[0:2]) and old_current_justified_checkpoint.epoch + 1 == current_epoch: state.finalized_checkpoint = old_current_justified_checkpoint ``` #### Inactivity scores *Note*: The function `process_inactivity_updates` is new. ```python def process_inactivity_updates(state: BeaconState) -> None: for index in get_eligible_validator_indices(state): if index in get_unslashed_participating_indices(state, TIMELY_TARGET_FLAG_INDEX, get_previous_epoch(state)): if state.inactivity_scores[index] > 0: state.inactivity_scores[index] -= 1 elif is_in_inactivity_leak(state): state.inactivity_scores[index] += INACTIVITY_SCORE_BIAS ``` #### Rewards and penalties *Note*: The function `process_rewards_and_penalties` is modified to support the incentive accounting reforms. ```python def process_rewards_and_penalties(state: BeaconState) -> None: # No rewards are applied at the end of `GENESIS_EPOCH` because rewards are for work done in the previous epoch if get_current_epoch(state) == GENESIS_EPOCH: return flag_indices_and_numerators = get_flag_indices_and_numerators() flag_deltas = [get_flag_index_deltas(state, index, numerator) for (index, numerator) in flag_indices_and_numerators] deltas = flag_deltas + [get_inactivity_penalty_deltas(state)] for (rewards, penalties) in deltas: for index in range(len(state.validators)): increase_balance(state, ValidatorIndex(index), rewards[index]) decrease_balance(state, ValidatorIndex(index), penalties[index]) ``` #### Slashings *Note*: The function `process_slashings` is modified to use `ALTAIR_PROPORTIONAL_SLASHING_MULTIPLIER`. ```python def process_slashings(state: BeaconState) -> None: epoch = get_current_epoch(state) total_balance = get_total_active_balance(state) adjusted_total_slashing_balance = min(sum(state.slashings) * ALTAIR_PROPORTIONAL_SLASHING_MULTIPLIER, total_balance) for index, validator in enumerate(state.validators): if validator.slashed and epoch + EPOCHS_PER_SLASHINGS_VECTOR // 2 == validator.withdrawable_epoch: increment = EFFECTIVE_BALANCE_INCREMENT # Factored out from penalty numerator to avoid uint64 overflow penalty_numerator = validator.effective_balance // increment * adjusted_total_slashing_balance penalty = penalty_numerator // total_balance * increment decrease_balance(state, ValidatorIndex(index), penalty) ``` #### Participation flags updates *Note*: The function `process_participation_flag_updates` is new. ```python def process_participation_flag_updates(state: BeaconState) -> None: state.previous_epoch_participation = state.current_epoch_participation state.current_epoch_participation = [ParticipationFlags(0b0000_0000) for _ in range(len(state.validators))] ``` #### Sync committee updates *Note*: The function `process_sync_committee_updates` is new. ```python def process_sync_committee_updates(state: BeaconState) -> None: 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) ```