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Altair -- The Beacon Chain

Introduction
Custom types
Constants
Preset
- Updated penalty values
- Sync committee
Configuration
- Inactivity penalties
Containers
- Modified containers
  - BeaconBlockBody
  - BeaconState
- New containers
  - SyncAggregate
  - SyncCommittee
Helper functions
Initialize state for pure Altair testnets and test vectors

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 towards their planned maximally punitive values

Custom types

Name	SSZ equivalent	Description
`ParticipationFlags`	`uint8`	a succinct representation of 8 boolean participation flags

Constants

Participation flag indices

Name	Value
`TIMELY_SOURCE_FLAG_INDEX`	`0`
`TIMELY_TARGET_FLAG_INDEX`	`1`
`TIMELY_HEAD_FLAG_INDEX`	`2`

Incentivization weights

Name	Value
`TIMELY_SOURCE_WEIGHT`	`uint64(14)`
`TIMELY_TARGET_WEIGHT`	`uint64(26)`
`TIMELY_HEAD_WEIGHT`	`uint64(14)`
`SYNC_REWARD_WEIGHT`	`uint64(2)`
`PROPOSER_WEIGHT`	`uint64(8)`
`WEIGHT_DENOMINATOR`	`uint64(64)`

Note: The sum of the weights equal WEIGHT_DENOMINATOR.

Domain types

Name	Value
`DOMAIN_SYNC_COMMITTEE`	`DomainType('0x07000000')`
`DOMAIN_SYNC_COMMITTEE_SELECTION_PROOF`	`DomainType('0x08000000')`
`DOMAIN_CONTRIBUTION_AND_PROOF`	`DomainType('0x09000000')`

Misc

Name	Value
`PARTICIPATION_FLAG_WEIGHTS`	`[TIMELY_SOURCE_WEIGHT, TIMELY_TARGET_WEIGHT, TIMELY_HEAD_WEIGHT]`

Preset

Updated penalty values

This patch updates a few configuration values to move penalty parameters closer to their final, maximum security values.

Note: The spec does not override previous configuration values but instead creates new values and replaces usage throughout.

Name	Value
`INACTIVITY_PENALTY_QUOTIENT_ALTAIR`	`uint64(3 * 2**24)` (= 50,331,648)
`MIN_SLASHING_PENALTY_QUOTIENT_ALTAIR`	`uint64(2**6)` (= 64)
`PROPORTIONAL_SLASHING_MULTIPLIER_ALTAIR`	`uint64(2)`

Sync committee

Name	Value	Unit	Duration
`SYNC_COMMITTEE_SIZE`	`uint64(2**9)` (= 512)	validators
`EPOCHS_PER_SYNC_COMMITTEE_PERIOD`	`uint64(2**8)` (= 256)	epochs	~27 hours

Configuration

Inactivity penalties

Name	Value	Description
`INACTIVITY_SCORE_BIAS`	`uint64(2**2)` (= 4)	score points per inactive epoch
`INACTIVITY_SCORE_RECOVERY_RATE`	`uint64(2**4)` (= 16)	score points per leak-free epoch

Containers

Modified containers

`BeaconBlockBody`

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_aggregate: SyncAggregate  # [New in Altair]

`BeaconState`

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

`SyncAggregate`

class SyncAggregate(Container):
    sync_committee_bits: Bitvector[SYNC_COMMITTEE_SIZE]
    sync_committee_signature: BLSSignature

`SyncCommittee`

class SyncCommittee(Container):
    pubkeys: Vector[BLSPubkey, SYNC_COMMITTEE_SIZE]
    aggregate_pubkey: BLSPubkey

Helper functions

Crypto

Refer to the definitions in the phase 0 document regarding BLS signatures and the extensions defined in the Altair BLS document. This specification assumes knowledge of the functionality described in those documents.

Misc

`add_flag`

def add_flag(flags: ParticipationFlags, flag_index: int) -> ParticipationFlags:
    """
    Return a new ``ParticipationFlags`` adding ``flag_index`` to ``flags``.
    """
    flag = ParticipationFlags(2**flag_index)
    return flags | flag

`has_flag`

def has_flag(flags: ParticipationFlags, flag_index: int) -> bool:
    """
    Return whether ``flags`` has ``flag_index`` set.
    """
    flag = ParticipationFlags(2**flag_index)
    return flags & flag == flag

Beacon state accessors

`get_next_sync_committee_indices`

def get_next_sync_committee_indices(state: BeaconState) -> Sequence[ValidatorIndex]:
    """
    Return the sync committee indices, with possible duplicates, for the next sync committee.
    """
    epoch = Epoch(get_current_epoch(state) + 1)

    MAX_RANDOM_BYTE = 2**8 - 1
    active_validator_indices = get_active_validator_indices(state, epoch)
    active_validator_count = uint64(len(active_validator_indices))
    seed = get_seed(state, 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:
            sync_committee_indices.append(candidate_index)
        i += 1
    return sync_committee_indices

`get_next_sync_committee`

Note: The function get_next_sync_committee should only be called at sync committee period boundaries and when upgrading state to Altair.

def get_next_sync_committee(state: BeaconState) -> SyncCommittee:
    """
    Return the next sync committee, with possible pubkey duplicates.
    """
    indices = get_next_sync_committee_indices(state)
    pubkeys = [state.validators[index].pubkey for index in indices]
    aggregate_pubkey = eth_aggregate_pubkeys(pubkeys)
    return SyncCommittee(pubkeys=pubkeys, aggregate_pubkey=aggregate_pubkey)

`get_base_reward_per_increment`

def get_base_reward_per_increment(state: BeaconState) -> Gwei:
    return Gwei(EFFECTIVE_BALANCE_INCREMENT * BASE_REWARD_FACTOR // integer_squareroot(get_total_active_balance(state)))

`get_base_reward`

Note: The function get_base_reward is modified with the removal of BASE_REWARDS_PER_EPOCH and the use of increment based accounting.

Note: On average an optimally performing validator earns one base reward per epoch.

def get_base_reward(state: BeaconState, index: ValidatorIndex) -> Gwei:
    """
    Return the base reward for the validator defined by ``index`` with respect to the current ``state``.
    """
    increments = state.validators[index].effective_balance // EFFECTIVE_BALANCE_INCREMENT
    return Gwei(increments * get_base_reward_per_increment(state))

`get_unslashed_participating_indices`

def get_unslashed_participating_indices(state: BeaconState, flag_index: int, epoch: Epoch) -> Set[ValidatorIndex]:
    """
    Return the set of validator indices that are both active and unslashed for the given ``flag_index`` and ``epoch``.
    """
    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_attestation_participation_flag_indices`

def get_attestation_participation_flag_indices(state: BeaconState,
                                               data: AttestationData,
                                               inclusion_delay: uint64) -> Sequence[int]:
    """
    Return the flag indices that are satisfied by an attestation.
    """
    if data.target.epoch == get_current_epoch(state):
        justified_checkpoint = state.current_justified_checkpoint
    else:
        justified_checkpoint = state.previous_justified_checkpoint

    # Matching roots
    is_matching_source = data.source == justified_checkpoint
    is_matching_target = is_matching_source and data.target.root == get_block_root(state, data.target.epoch)
    is_matching_head = is_matching_target and data.beacon_block_root == get_block_root_at_slot(state, data.slot)
    assert is_matching_source

    participation_flag_indices = []
    if is_matching_source and inclusion_delay <= integer_squareroot(SLOTS_PER_EPOCH):
        participation_flag_indices.append(TIMELY_SOURCE_FLAG_INDEX)
    if is_matching_target and inclusion_delay <= SLOTS_PER_EPOCH:
        participation_flag_indices.append(TIMELY_TARGET_FLAG_INDEX)
    if is_matching_head and inclusion_delay == MIN_ATTESTATION_INCLUSION_DELAY:
        participation_flag_indices.append(TIMELY_HEAD_FLAG_INDEX)

    return participation_flag_indices

`get_flag_index_deltas`

def get_flag_index_deltas(state: BeaconState, flag_index: int) -> 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)
    previous_epoch = get_previous_epoch(state)
    unslashed_participating_indices = get_unslashed_participating_indices(state, flag_index, previous_epoch)
    weight = PARTICIPATION_FLAG_WEIGHTS[flag_index]
    unslashed_participating_balance = get_total_balance(state, unslashed_participating_indices)
    unslashed_participating_increments = unslashed_participating_balance // EFFECTIVE_BALANCE_INCREMENT
    active_increments = get_total_active_balance(state) // EFFECTIVE_BALANCE_INCREMENT
    for index in get_eligible_validator_indices(state):
        base_reward = get_base_reward(state, index)
        if index in unslashed_participating_indices:
            if not is_in_inactivity_leak(state):
                reward_numerator = base_reward * weight * unslashed_participating_increments
                rewards[index] += Gwei(reward_numerator // (active_increments * WEIGHT_DENOMINATOR))
        elif flag_index != TIMELY_HEAD_FLAG_INDEX:
            penalties[index] += Gwei(base_reward * weight // WEIGHT_DENOMINATOR)
    return rewards, penalties

Modified `get_inactivity_penalty_deltas`

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))]
    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):
        if index not in matching_target_indices:
            penalty_numerator = state.validators[index].effective_balance * state.inactivity_scores[index]
            penalty_denominator = INACTIVITY_SCORE_BIAS * INACTIVITY_PENALTY_QUOTIENT_ALTAIR
            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 MIN_SLASHING_PENALTY_QUOTIENT_ALTAIR and use PROPOSER_WEIGHT when calculating the proposer reward.

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 // MIN_SLASHING_PENALTY_QUOTIENT_ALTAIR)

    # 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_WEIGHT // WEIGHT_DENOMINATOR)
    increase_balance(state, proposer_index, proposer_reward)
    increase_balance(state, whistleblower_index, Gwei(whistleblower_reward - proposer_reward))

Block processing

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_aggregate(state, block.body.sync_aggregate)  # [New in Altair]

Modified `process_attestation`

Note: The function process_attestation is modified to do incentive accounting with epoch participation flags.

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)

    # Participation flag indices
    participation_flag_indices = get_attestation_participation_flag_indices(state, data, state.slot - data.slot)

    # Verify signature
    assert is_valid_indexed_attestation(state, get_indexed_attestation(state, attestation))

    # Update epoch participation flags
    if data.target.epoch == get_current_epoch(state):
        epoch_participation = state.current_epoch_participation
    else:
        epoch_participation = state.previous_epoch_participation

    proposer_reward_numerator = 0
    for index in get_attesting_indices(state, data, attestation.aggregation_bits):
        for flag_index, weight in enumerate(PARTICIPATION_FLAG_WEIGHTS):
            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) * weight

    # Reward proposer
    proposer_reward_denominator = (WEIGHT_DENOMINATOR - PROPOSER_WEIGHT) * WEIGHT_DENOMINATOR // PROPOSER_WEIGHT
    proposer_reward = Gwei(proposer_reward_numerator // proposer_reward_denominator)
    increase_balance(state, get_beacon_proposer_index(state), proposer_reward)

Modified `apply_deposit`

Note: The function apply_deposit is modified to initialize inactivity_scores, previous_epoch_participation, and current_epoch_participation.

def apply_deposit(state: BeaconState,
                  pubkey: BLSPubkey,
                  withdrawal_credentials: Bytes32,
                  amount: uint64,
                  signature: BLSSignature) -> None:
    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=pubkey,
            withdrawal_credentials=withdrawal_credentials,
            amount=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, signature):
            state.validators.append(get_validator_from_deposit(pubkey, withdrawal_credentials, amount))
            state.balances.append(amount)
            # [New in Altair]
            state.previous_epoch_participation.append(ParticipationFlags(0b0000_0000))
            state.current_epoch_participation.append(ParticipationFlags(0b0000_0000))
            state.inactivity_scores.append(uint64(0))
    else:
        # Increase balance by deposit amount
        index = ValidatorIndex(validator_pubkeys.index(pubkey))
        increase_balance(state, index, amount)

Sync aggregate processing

Note: The function process_sync_aggregate is new.

def process_sync_aggregate(state: BeaconState, sync_aggregate: SyncAggregate) -> None:
    # Verify sync committee aggregate signature signing over the previous slot block root
    committee_pubkeys = state.current_sync_committee.pubkeys
    participant_pubkeys = [pubkey for pubkey, bit in zip(committee_pubkeys, sync_aggregate.sync_committee_bits) if bit]
    previous_slot = max(state.slot, Slot(1)) - Slot(1)
    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 eth_fast_aggregate_verify(participant_pubkeys, signing_root, sync_aggregate.sync_committee_signature)

    # Compute participant and proposer rewards
    total_active_increments = get_total_active_balance(state) // EFFECTIVE_BALANCE_INCREMENT
    total_base_rewards = Gwei(get_base_reward_per_increment(state) * total_active_increments)
    max_participant_rewards = Gwei(total_base_rewards * SYNC_REWARD_WEIGHT // WEIGHT_DENOMINATOR // SLOTS_PER_EPOCH)
    participant_reward = Gwei(max_participant_rewards // SYNC_COMMITTEE_SIZE)
    proposer_reward = Gwei(participant_reward * PROPOSER_WEIGHT // (WEIGHT_DENOMINATOR - PROPOSER_WEIGHT))

    # Apply participant and proposer rewards
    all_pubkeys = [v.pubkey for v in state.validators]
    committee_indices = [ValidatorIndex(all_pubkeys.index(pubkey)) for pubkey in state.current_sync_committee.pubkeys]
    for participant_index, participation_bit in zip(committee_indices, sync_aggregate.sync_committee_bits):
        if participation_bit:
            increase_balance(state, participant_index, participant_reward)
            increase_balance(state, get_beacon_proposer_index(state), proposer_reward)
        else:
            decrease_balance(state, participant_index, participant_reward)

Epoch processing

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 to adapt to the new participation records.

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_indices = get_unslashed_participating_indices(state, TIMELY_TARGET_FLAG_INDEX, get_previous_epoch(state))
    current_indices = get_unslashed_participating_indices(state, TIMELY_TARGET_FLAG_INDEX, get_current_epoch(state))
    total_active_balance = get_total_active_balance(state)
    previous_target_balance = get_total_balance(state, previous_indices)
    current_target_balance = get_total_balance(state, current_indices)
    weigh_justification_and_finalization(state, total_active_balance, previous_target_balance, current_target_balance)

Inactivity scores

Note: The function process_inactivity_updates is new.

def process_inactivity_updates(state: BeaconState) -> None:
    # Skip the genesis epoch as score updates are based on the previous epoch participation
    if get_current_epoch(state) == GENESIS_EPOCH:
        return

    for index in get_eligible_validator_indices(state):
        # Increase the inactivity score of inactive validators
        if index in get_unslashed_participating_indices(state, TIMELY_TARGET_FLAG_INDEX, get_previous_epoch(state)):
            state.inactivity_scores[index] -= min(1, state.inactivity_scores[index])
        else:
            state.inactivity_scores[index] += INACTIVITY_SCORE_BIAS
        # Decrease the inactivity score of all eligible validators during a leak-free epoch
        if not is_in_inactivity_leak(state):
            state.inactivity_scores[index] -= min(INACTIVITY_SCORE_RECOVERY_RATE, state.inactivity_scores[index])

Rewards and penalties

Note: The function process_rewards_and_penalties is modified to support the incentive accounting reforms.

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_deltas = [get_flag_index_deltas(state, flag_index) for flag_index in range(len(PARTICIPATION_FLAG_WEIGHTS))]
    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 PROPORTIONAL_SLASHING_MULTIPLIER_ALTAIR.

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) * PROPORTIONAL_SLASHING_MULTIPLIER_ALTAIR, 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.

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.

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_next_sync_committee(state)

Initialize state for pure Altair testnets and test vectors

This helper function is only for initializing the state for pure Altair testnets and tests.

Note: The function initialize_beacon_state_from_eth1 is modified: (1) using ALTAIR_FORK_VERSION as the previous and current fork version, (2) utilizing the Altair BeaconBlockBody when constructing the initial latest_block_header, and (3) adding initial sync committees.

def initialize_beacon_state_from_eth1(eth1_block_hash: Hash32,
                                      eth1_timestamp: uint64,
                                      deposits: Sequence[Deposit]) -> BeaconState:
    fork = Fork(
        previous_version=ALTAIR_FORK_VERSION,  # [Modified in Altair] for testing only
        current_version=ALTAIR_FORK_VERSION,  # [Modified in Altair]
        epoch=GENESIS_EPOCH,
    )
    state = BeaconState(
        genesis_time=eth1_timestamp + GENESIS_DELAY,
        fork=fork,
        eth1_data=Eth1Data(block_hash=eth1_block_hash, deposit_count=uint64(len(deposits))),
        latest_block_header=BeaconBlockHeader(body_root=hash_tree_root(BeaconBlockBody())),
        randao_mixes=[eth1_block_hash] * EPOCHS_PER_HISTORICAL_VECTOR,  # Seed RANDAO with Eth1 entropy
    )

    # Process deposits
    leaves = list(map(lambda deposit: deposit.data, deposits))
    for index, deposit in enumerate(deposits):
        deposit_data_list = List[DepositData, 2**DEPOSIT_CONTRACT_TREE_DEPTH](*leaves[:index + 1])
        state.eth1_data.deposit_root = hash_tree_root(deposit_data_list)
        process_deposit(state, deposit)

    # Process activations
    for index, validator in enumerate(state.validators):
        balance = state.balances[index]
        validator.effective_balance = min(balance - balance % EFFECTIVE_BALANCE_INCREMENT, MAX_EFFECTIVE_BALANCE)
        if validator.effective_balance == MAX_EFFECTIVE_BALANCE:
            validator.activation_eligibility_epoch = GENESIS_EPOCH
            validator.activation_epoch = GENESIS_EPOCH

    # Set genesis validators root for domain separation and chain versioning
    state.genesis_validators_root = hash_tree_root(state.validators)

    # [New in Altair] Fill in sync committees
    # Note: A duplicate committee is assigned for the current and next committee at genesis
    state.current_sync_committee = get_next_sync_committee(state)
    state.next_sync_committee = get_next_sync_committee(state)

    return state

30 KiB Raw Blame History

Altair -- The Beacon Chain

Table of contents

Introduction

Custom types

Constants

Participation flag indices

Incentivization weights

Domain types

Misc

Preset

Updated penalty values

Sync committee

Configuration

Inactivity penalties

Containers

Modified containers

BeaconBlockBody

BeaconState

New containers

SyncAggregate

SyncCommittee

Helper functions

Crypto

Misc

add_flag

has_flag

Beacon state accessors

get_next_sync_committee_indices

get_next_sync_committee

get_base_reward_per_increment

get_base_reward

get_unslashed_participating_indices

get_attestation_participation_flag_indices

get_flag_index_deltas

Modified get_inactivity_penalty_deltas

Beacon state mutators

Modified slash_validator

Block processing

Modified process_attestation

Modified apply_deposit

Sync aggregate processing

Epoch processing

Justification and finalization

Inactivity scores

Rewards and penalties

Slashings

Participation flags updates

Sync committee updates

Initialize state for pure Altair testnets and test vectors

30 KiB

Raw Blame History

`BeaconBlockBody`

`BeaconState`

`SyncAggregate`

`SyncCommittee`

`add_flag`

`has_flag`

`get_next_sync_committee_indices`

`get_next_sync_committee`

`get_base_reward_per_increment`

`get_base_reward`

`get_unslashed_participating_indices`

`get_attestation_participation_flag_indices`

`get_flag_index_deltas`

Modified `get_inactivity_penalty_deltas`

Modified `slash_validator`

Modified `process_attestation`

Modified `apply_deposit`