59 KiB
Ethereum 2.0 Phase 0 -- The Beacon Chain
Notice: This document is a work-in-progress for researchers and implementers.
Table of contents
- Introduction
- Notation
- Custom types
- Constants
- Configuration
- Containers
- Helper functions
- Math
- Crypto
- Predicates
- Misc
- Beacon state accessors
get_current_epoch
get_previous_epoch
get_block_root
get_block_root_at_slot
get_randao_mix
get_active_validator_indices
get_validator_churn_limit
get_seed
get_committee_count_at_slot
get_beacon_committee
get_beacon_proposer_index
get_total_balance
get_total_active_balance
get_domain
get_indexed_attestation
get_attesting_indices
- Beacon state mutators
- Genesis
- Beacon chain state transition function
Introduction
This document represents the specification for Phase 0 of Ethereum 2.0 -- The Beacon Chain.
At the core of Ethereum 2.0 is a system chain called the "beacon chain". The beacon chain stores and manages the registry of validators. In the initial deployment phases of Ethereum 2.0, the only mechanism to become a validator is to make a one-way ETH transaction to a deposit contract on Ethereum 1.0. Activation as a validator happens when Ethereum 1.0 deposit receipts are processed by the beacon chain, the activation balance is reached, and a queuing process is completed. Exit is either voluntary or done forcibly as a penalty for misbehavior. The primary source of load on the beacon chain is "attestations". Attestations are simultaneously availability votes for a shard block (Phase 1) and proof-of-stake votes for a beacon block (Phase 0).
Notation
Code snippets appearing in this style
are to be interpreted as Python 3 code.
Custom types
We define the following Python custom types for type hinting and readability:
Name | SSZ equivalent | Description |
---|---|---|
Slot |
uint64 |
a slot number |
Epoch |
uint64 |
an epoch number |
CommitteeIndex |
uint64 |
a committee index at a slot |
ValidatorIndex |
uint64 |
a validator registry index |
Gwei |
uint64 |
an amount in Gwei |
Root |
Bytes32 |
a Merkle root |
Version |
Bytes4 |
a fork version number |
DomainType |
Bytes4 |
a domain type |
Domain |
Bytes8 |
a signature domain |
BLSPubkey |
Bytes48 |
a BLS12-381 public key |
BLSSignature |
Bytes96 |
a BLS12-381 signature |
Constants
The following values are (non-configurable) constants used throughout the specification.
Name | Value |
---|---|
GENESIS_SLOT |
Slot(0) |
GENESIS_EPOCH |
Epoch(0) |
FAR_FUTURE_EPOCH |
Epoch(2**64 - 1) |
BASE_REWARDS_PER_EPOCH |
4 |
DEPOSIT_CONTRACT_TREE_DEPTH |
2**5 (= 32) |
JUSTIFICATION_BITS_LENGTH |
4 |
ENDIANNESS |
'little' |
Configuration
Note: The default mainnet configuration values are included here for spec-design purposes. The different configurations for mainnet, testnets, and YAML-based testing can be found in the configs/constant_presets
directory. These configurations are updated for releases and may be out of sync during dev
changes.
Misc
Name | Value |
---|---|
MAX_COMMITTEES_PER_SLOT |
2**6 (= 64) |
TARGET_COMMITTEE_SIZE |
2**7 (= 128) |
MAX_VALIDATORS_PER_COMMITTEE |
2**11 (= 2,048) |
MIN_PER_EPOCH_CHURN_LIMIT |
2**2 (= 4) |
CHURN_LIMIT_QUOTIENT |
2**16 (= 65,536) |
SHUFFLE_ROUND_COUNT |
90 |
MIN_GENESIS_ACTIVE_VALIDATOR_COUNT |
2**14 (= 16,384) |
MIN_GENESIS_TIME |
1578009600 (Jan 3, 2020) |
- For the safety of committees,
TARGET_COMMITTEE_SIZE
exceeds the recommended minimum committee size of 111; with sufficient active validators (at leastSLOTS_PER_EPOCH * TARGET_COMMITTEE_SIZE
), the shuffling algorithm ensures committee sizes of at leastTARGET_COMMITTEE_SIZE
. (Unbiasable randomness with a Verifiable Delay Function (VDF) will improve committee robustness and lower the safe minimum committee size.)
Gwei values
Name | Value |
---|---|
MIN_DEPOSIT_AMOUNT |
Gwei(2**0 * 10**9) (= 1,000,000,000) |
MAX_EFFECTIVE_BALANCE |
Gwei(2**5 * 10**9) (= 32,000,000,000) |
EJECTION_BALANCE |
Gwei(2**4 * 10**9) (= 16,000,000,000) |
EFFECTIVE_BALANCE_INCREMENT |
Gwei(2**0 * 10**9) (= 1,000,000,000) |
Initial values
Name | Value |
---|---|
GENESIS_FORK_VERSION |
Version('0x00000000') |
BLS_WITHDRAWAL_PREFIX |
Bytes1('0x00') |
Time parameters
Name | Value | Unit | Duration |
---|---|---|---|
MIN_GENESIS_DELAY |
86400 |
seconds | 1 day |
SECONDS_PER_SLOT |
12 |
seconds | 12 seconds |
MIN_ATTESTATION_INCLUSION_DELAY |
2**0 (= 1) |
slots | 12 seconds |
SLOTS_PER_EPOCH |
2**5 (= 32) |
slots | 6.4 minutes |
MIN_SEED_LOOKAHEAD |
2**0 (= 1) |
epochs | 6.4 minutes |
MAX_SEED_LOOKAHEAD |
2**2 (= 4) |
epochs | 25.6 minutes |
MIN_EPOCHS_TO_INACTIVITY_PENALTY |
2**2 (= 4) |
epochs | 25.6 minutes |
EPOCHS_PER_ETH1_VOTING_PERIOD |
2**5 (= 32) |
epochs | ~3.4 hours |
SLOTS_PER_HISTORICAL_ROOT |
2**13 (= 8,192) |
slots | ~27 hours |
MIN_VALIDATOR_WITHDRAWABILITY_DELAY |
2**8 (= 256) |
epochs | ~27 hours |
PERSISTENT_COMMITTEE_PERIOD |
2**11 (= 2,048) |
epochs | 9 days |
State list lengths
Name | Value | Unit | Duration |
---|---|---|---|
EPOCHS_PER_HISTORICAL_VECTOR |
2**16 (= 65,536) |
epochs | ~0.8 years |
EPOCHS_PER_SLASHINGS_VECTOR |
2**13 (= 8,192) |
epochs | ~36 days |
HISTORICAL_ROOTS_LIMIT |
2**24 (= 16,777,216) |
historical roots | ~52,262 years |
VALIDATOR_REGISTRY_LIMIT |
2**40 (= 1,099,511,627,776) |
validators |
Rewards and penalties
Name | Value |
---|---|
BASE_REWARD_FACTOR |
2**6 (= 64) |
WHISTLEBLOWER_REWARD_QUOTIENT |
2**9 (= 512) |
PROPOSER_REWARD_QUOTIENT |
2**3 (= 8) |
INACTIVITY_PENALTY_QUOTIENT |
2**25 (= 33,554,432) |
MIN_SLASHING_PENALTY_QUOTIENT |
2**5 (= 32) |
- The
INACTIVITY_PENALTY_QUOTIENT
equalsINVERSE_SQRT_E_DROP_TIME**2
whereINVERSE_SQRT_E_DROP_TIME := 2**12 epochs
(about 18 days) is the time it takes the inactivity penalty to reduce the balance of non-participating validators to about1/sqrt(e) ~= 60.6%
. Indeed, the balance retained by offline validators aftern
epochs is about(1 - 1/INACTIVITY_PENALTY_QUOTIENT)**(n**2/2)
; so afterINVERSE_SQRT_E_DROP_TIME
epochs, it is roughly(1 - 1/INACTIVITY_PENALTY_QUOTIENT)**(INACTIVITY_PENALTY_QUOTIENT/2) ~= 1/sqrt(e)
.
Max operations per block
Name | Value |
---|---|
MAX_PROPOSER_SLASHINGS |
2**4 (= 16) |
MAX_ATTESTER_SLASHINGS |
2**0 (= 1) |
MAX_ATTESTATIONS |
2**7 (= 128) |
MAX_DEPOSITS |
2**4 (= 16) |
MAX_VOLUNTARY_EXITS |
2**4 (= 16) |
Domain types
Name | Value |
---|---|
DOMAIN_BEACON_PROPOSER |
DomainType('0x00000000') |
DOMAIN_BEACON_ATTESTER |
DomainType('0x01000000') |
DOMAIN_RANDAO |
DomainType('0x02000000') |
DOMAIN_DEPOSIT |
DomainType('0x03000000') |
DOMAIN_VOLUNTARY_EXIT |
DomainType('0x04000000') |
DOMAIN_SELECTION_PROOF |
DomainType('0x05000000') |
DOMAIN_AGGREGATE_AND_PROOF |
DomainType('0x06000000') |
Containers
The following types are SimpleSerialize (SSZ) containers.
Note: The definitions are ordered topologically to facilitate execution of the spec.
Note: Fields missing in container instantiations default to their zero value.
Misc dependencies
Fork
class Fork(Container):
previous_version: Version
current_version: Version
epoch: Epoch # Epoch of latest fork
Checkpoint
class Checkpoint(Container):
epoch: Epoch
root: Root
Validator
class Validator(Container):
pubkey: BLSPubkey
withdrawal_credentials: Bytes32 # Commitment to pubkey for withdrawals
effective_balance: Gwei # Balance at stake
slashed: boolean
# Status epochs
activation_eligibility_epoch: Epoch # When criteria for activation were met
activation_epoch: Epoch
exit_epoch: Epoch
withdrawable_epoch: Epoch # When validator can withdraw funds
AttestationData
class AttestationData(Container):
slot: Slot
index: CommitteeIndex
# LMD GHOST vote
beacon_block_root: Root
# FFG vote
source: Checkpoint
target: Checkpoint
IndexedAttestation
class IndexedAttestation(Container):
attesting_indices: List[ValidatorIndex, MAX_VALIDATORS_PER_COMMITTEE]
data: AttestationData
signature: BLSSignature
PendingAttestation
class PendingAttestation(Container):
aggregation_bits: Bitlist[MAX_VALIDATORS_PER_COMMITTEE]
data: AttestationData
inclusion_delay: Slot
proposer_index: ValidatorIndex
Eth1Data
class Eth1Data(Container):
deposit_root: Root
deposit_count: uint64
block_hash: Bytes32
HistoricalBatch
class HistoricalBatch(Container):
block_roots: Vector[Root, SLOTS_PER_HISTORICAL_ROOT]
state_roots: Vector[Root, SLOTS_PER_HISTORICAL_ROOT]
DepositMessage
class DepositMessage(Container):
pubkey: BLSPubkey
withdrawal_credentials: Bytes32
amount: Gwei
DepositData
class DepositData(Container):
pubkey: BLSPubkey
withdrawal_credentials: Bytes32
amount: Gwei
signature: BLSSignature # Signing over DepositMessage
BeaconBlockHeader
class BeaconBlockHeader(Container):
slot: Slot
parent_root: Root
state_root: Root
body_root: Root
SigningRoot
class SigningRoot(Container):
object_root: Root
domain: Domain
Beacon operations
ProposerSlashing
class ProposerSlashing(Container):
proposer_index: ValidatorIndex
signed_header_1: SignedBeaconBlockHeader
signed_header_2: SignedBeaconBlockHeader
AttesterSlashing
class AttesterSlashing(Container):
attestation_1: IndexedAttestation
attestation_2: IndexedAttestation
Attestation
class Attestation(Container):
aggregation_bits: Bitlist[MAX_VALIDATORS_PER_COMMITTEE]
data: AttestationData
signature: BLSSignature
Deposit
class Deposit(Container):
proof: Vector[Bytes32, DEPOSIT_CONTRACT_TREE_DEPTH + 1] # Merkle path to deposit root
data: DepositData
VoluntaryExit
class VoluntaryExit(Container):
epoch: Epoch # Earliest epoch when voluntary exit can be processed
validator_index: ValidatorIndex
Beacon blocks
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]
BeaconBlock
class BeaconBlock(Container):
slot: Slot
parent_root: Root
state_root: Root
body: BeaconBlockBody
Beacon state
BeaconState
class BeaconState(Container):
# Versioning
genesis_time: uint64
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
# Attestations
previous_epoch_attestations: List[PendingAttestation, MAX_ATTESTATIONS * SLOTS_PER_EPOCH]
current_epoch_attestations: List[PendingAttestation, MAX_ATTESTATIONS * SLOTS_PER_EPOCH]
# Finality
justification_bits: Bitvector[JUSTIFICATION_BITS_LENGTH] # Bit set for every recent justified epoch
previous_justified_checkpoint: Checkpoint # Previous epoch snapshot
current_justified_checkpoint: Checkpoint
finalized_checkpoint: Checkpoint
Signed envelopes
SignedVoluntaryExit
class SignedVoluntaryExit(Container):
message: VoluntaryExit
signature: BLSSignature
SignedBeaconBlock
class SignedBeaconBlock(Container):
message: BeaconBlock
signature: BLSSignature
SignedBeaconBlockHeader
class SignedBeaconBlockHeader(Container):
message: BeaconBlockHeader
signature: BLSSignature
Helper functions
Note: The definitions below are for specification purposes and are not necessarily optimal implementations.
Math
integer_squareroot
def integer_squareroot(n: uint64) -> uint64:
"""
Return the largest integer ``x`` such that ``x**2 <= n``.
"""
x = n
y = (x + 1) // 2
while y < x:
x = y
y = (x + n // x) // 2
return x
xor
def xor(bytes_1: Bytes32, bytes_2: Bytes32) -> Bytes32:
"""
Return the exclusive-or of two 32-byte strings.
"""
return Bytes32(a ^ b for a, b in zip(bytes_1, bytes_2))
int_to_bytes
def int_to_bytes(n: uint64, length: uint64) -> bytes:
"""
Return the ``length``-byte serialization of ``n`` in ``ENDIANNESS``-endian.
"""
return n.to_bytes(length, ENDIANNESS)
bytes_to_int
def bytes_to_int(data: bytes) -> uint64:
"""
Return the integer deserialization of ``data`` interpreted as ``ENDIANNESS``-endian.
"""
return int.from_bytes(data, ENDIANNESS)
Crypto
hash
def hash(data: bytes) -> Bytes32
is SHA256.
hash_tree_root
def hash_tree_root(object: SSZSerializable) -> Root
is a function for hashing objects into a single root by utilizing a hash tree structure, as defined in the SSZ spec.
BLS Signatures
Eth2 makes use of BLS signatures as specified in the IETF draft BLS specification. Specifically, eth2 uses the BLS_SIG_BLS12381G2-SHA256-SSWU-RO-_POP_
ciphersuite which implements the following interfaces:
def Sign(SK: int, message: Bytes) -> BLSSignature
def Verify(PK: BLSPubkey, message: Bytes, signature: BLSSignature) -> bool
def Aggregate(signatures: Sequence[BLSSignature]) -> BLSSignature
def FastAggregateVerify(PKs: Sequence[BLSPubkey], message: Bytes, signature: BLSSignature) -> bool
def AggregateVerify(pairs: Sequence[PK: BLSPubkey, message: Bytes], signature: BLSSignature) -> bool
Within these specifications, BLS signatures are treated as a module for notational clarity, thus to verify a signature bls.Verify(...)
is used.
Predicates
is_active_validator
def is_active_validator(validator: Validator, epoch: Epoch) -> bool:
"""
Check if ``validator`` is active.
"""
return validator.activation_epoch <= epoch < validator.exit_epoch
is_eligible_for_activation_queue
def is_eligible_for_activation_queue(validator: Validator) -> bool:
"""
Check if ``validator`` is eligible to be placed into the activation queue.
"""
return (
validator.activation_eligibility_epoch == FAR_FUTURE_EPOCH
and validator.effective_balance == MAX_EFFECTIVE_BALANCE
)
is_eligible_for_activation
def is_eligible_for_activation(state: BeaconState, validator: Validator) -> bool:
"""
Check if ``validator`` is eligible for activation.
"""
return (
# Placement in queue is finalized
validator.activation_eligibility_epoch <= state.finalized_checkpoint.epoch
# Has not yet been activated
and validator.activation_epoch == FAR_FUTURE_EPOCH
)
is_slashable_validator
def is_slashable_validator(validator: Validator, epoch: Epoch) -> bool:
"""
Check if ``validator`` is slashable.
"""
return (not validator.slashed) and (validator.activation_epoch <= epoch < validator.withdrawable_epoch)
is_slashable_attestation_data
def is_slashable_attestation_data(data_1: AttestationData, data_2: AttestationData) -> bool:
"""
Check if ``data_1`` and ``data_2`` are slashable according to Casper FFG rules.
"""
return (
# Double vote
(data_1 != data_2 and data_1.target.epoch == data_2.target.epoch) or
# Surround vote
(data_1.source.epoch < data_2.source.epoch and data_2.target.epoch < data_1.target.epoch)
)
is_valid_indexed_attestation
def is_valid_indexed_attestation(state: BeaconState, indexed_attestation: IndexedAttestation) -> bool:
"""
Check if ``indexed_attestation`` has valid indices and signature.
"""
indices = indexed_attestation.attesting_indices
# Verify max number of indices
if not len(indices) <= MAX_VALIDATORS_PER_COMMITTEE:
return False
# Verify indices are sorted and unique
if not indices == sorted(set(indices)):
return False
# Verify aggregate signature
pubkeys = [state.validators[i].pubkey for i in indices]
domain = get_domain(state, DOMAIN_BEACON_ATTESTER, indexed_attestation.data.target.epoch)
signing_root = compute_signing_root(indexed_attestation.data, domain)
return bls.FastAggregateVerify(pubkeys, signing_root, indexed_attestation.signature)
is_valid_merkle_branch
def is_valid_merkle_branch(leaf: Bytes32, branch: Sequence[Bytes32], depth: uint64, index: uint64, root: Root) -> bool:
"""
Check if ``leaf`` at ``index`` verifies against the Merkle ``root`` and ``branch``.
"""
value = leaf
for i in range(depth):
if index // (2**i) % 2:
value = hash(branch[i] + value)
else:
value = hash(value + branch[i])
return value == root
Misc
compute_shuffled_index
def compute_shuffled_index(index: ValidatorIndex, index_count: uint64, seed: Bytes32) -> ValidatorIndex:
"""
Return the shuffled validator index corresponding to ``seed`` (and ``index_count``).
"""
assert index < index_count
# Swap or not (https://link.springer.com/content/pdf/10.1007%2F978-3-642-32009-5_1.pdf)
# See the 'generalized domain' algorithm on page 3
for current_round in range(SHUFFLE_ROUND_COUNT):
pivot = bytes_to_int(hash(seed + int_to_bytes(current_round, length=1))[0:8]) % index_count
flip = ValidatorIndex((pivot + index_count - index) % index_count)
position = max(index, flip)
source = hash(seed + int_to_bytes(current_round, length=1) + int_to_bytes(position // 256, length=4))
byte = source[(position % 256) // 8]
bit = (byte >> (position % 8)) % 2
index = flip if bit else index
return ValidatorIndex(index)
compute_proposer_index
def compute_proposer_index(state: BeaconState, indices: Sequence[ValidatorIndex], seed: Bytes32) -> ValidatorIndex:
"""
Return from ``indices`` a random index sampled by effective balance.
"""
assert len(indices) > 0
MAX_RANDOM_BYTE = 2**8 - 1
i = 0
while True:
candidate_index = indices[compute_shuffled_index(ValidatorIndex(i % len(indices)), len(indices), seed)]
random_byte = hash(seed + int_to_bytes(i // 32, length=8))[i % 32]
effective_balance = state.validators[candidate_index].effective_balance
if effective_balance * MAX_RANDOM_BYTE >= MAX_EFFECTIVE_BALANCE * random_byte:
return ValidatorIndex(candidate_index)
i += 1
compute_committee
def compute_committee(indices: Sequence[ValidatorIndex],
seed: Bytes32,
index: uint64,
count: uint64) -> Sequence[ValidatorIndex]:
"""
Return the committee corresponding to ``indices``, ``seed``, ``index``, and committee ``count``.
"""
start = (len(indices) * index) // count
end = (len(indices) * (index + 1)) // count
return [indices[compute_shuffled_index(ValidatorIndex(i), len(indices), seed)] for i in range(start, end)]
compute_epoch_at_slot
def compute_epoch_at_slot(slot: Slot) -> Epoch:
"""
Return the epoch number at ``slot``.
"""
return Epoch(slot // SLOTS_PER_EPOCH)
compute_start_slot_at_epoch
def compute_start_slot_at_epoch(epoch: Epoch) -> Slot:
"""
Return the start slot of ``epoch``.
"""
return Slot(epoch * SLOTS_PER_EPOCH)
compute_activation_exit_epoch
def compute_activation_exit_epoch(epoch: Epoch) -> Epoch:
"""
Return the epoch during which validator activations and exits initiated in ``epoch`` take effect.
"""
return Epoch(epoch + 1 + MAX_SEED_LOOKAHEAD)
compute_domain
def compute_domain(domain_type: DomainType, fork_version: Optional[Version]=None) -> Domain:
"""
Return the domain for the ``domain_type`` and ``fork_version``.
"""
if fork_version is None:
fork_version = GENESIS_FORK_VERSION
return Domain(domain_type + fork_version)
compute_signing_root
def compute_signing_root(ssz_object: SSZObject, domain: Domain) -> Root:
"""
Return the signing root of an object by calculating the root of the object-domain tree.
"""
domain_wrapped_object = SigningRoot(
object_root=hash_tree_root(ssz_object),
domain=domain,
)
return hash_tree_root(domain_wrapped_object)
Beacon state accessors
get_current_epoch
def get_current_epoch(state: BeaconState) -> Epoch:
"""
Return the current epoch.
"""
return compute_epoch_at_slot(state.slot)
get_previous_epoch
def get_previous_epoch(state: BeaconState) -> Epoch:
"""`
Return the previous epoch (unless the current epoch is ``GENESIS_EPOCH``).
"""
current_epoch = get_current_epoch(state)
return GENESIS_EPOCH if current_epoch == GENESIS_EPOCH else Epoch(current_epoch - 1)
get_block_root
def get_block_root(state: BeaconState, epoch: Epoch) -> Root:
"""
Return the block root at the start of a recent ``epoch``.
"""
return get_block_root_at_slot(state, compute_start_slot_at_epoch(epoch))
get_block_root_at_slot
def get_block_root_at_slot(state: BeaconState, slot: Slot) -> Root:
"""
Return the block root at a recent ``slot``.
"""
assert slot < state.slot <= slot + SLOTS_PER_HISTORICAL_ROOT
return state.block_roots[slot % SLOTS_PER_HISTORICAL_ROOT]
get_randao_mix
def get_randao_mix(state: BeaconState, epoch: Epoch) -> Bytes32:
"""
Return the randao mix at a recent ``epoch``.
"""
return state.randao_mixes[epoch % EPOCHS_PER_HISTORICAL_VECTOR]
get_active_validator_indices
def get_active_validator_indices(state: BeaconState, epoch: Epoch) -> Sequence[ValidatorIndex]:
"""
Return the sequence of active validator indices at ``epoch``.
"""
return [ValidatorIndex(i) for i, v in enumerate(state.validators) if is_active_validator(v, epoch)]
get_validator_churn_limit
def get_validator_churn_limit(state: BeaconState) -> uint64:
"""
Return the validator churn limit for the current epoch.
"""
active_validator_indices = get_active_validator_indices(state, get_current_epoch(state))
return max(MIN_PER_EPOCH_CHURN_LIMIT, len(active_validator_indices) // CHURN_LIMIT_QUOTIENT)
get_seed
def get_seed(state: BeaconState, epoch: Epoch, domain_type: DomainType) -> Bytes32:
"""
Return the seed at ``epoch``.
"""
mix = get_randao_mix(state, Epoch(epoch + EPOCHS_PER_HISTORICAL_VECTOR - MIN_SEED_LOOKAHEAD - 1)) # Avoid underflow
return hash(domain_type + int_to_bytes(epoch, length=8) + mix)
get_committee_count_at_slot
def get_committee_count_at_slot(state: BeaconState, slot: Slot) -> uint64:
"""
Return the number of committees at ``slot``.
"""
epoch = compute_epoch_at_slot(slot)
return max(1, min(
MAX_COMMITTEES_PER_SLOT,
len(get_active_validator_indices(state, epoch)) // SLOTS_PER_EPOCH // TARGET_COMMITTEE_SIZE,
))
get_beacon_committee
def get_beacon_committee(state: BeaconState, slot: Slot, index: CommitteeIndex) -> Sequence[ValidatorIndex]:
"""
Return the beacon committee at ``slot`` for ``index``.
"""
epoch = compute_epoch_at_slot(slot)
committees_per_slot = get_committee_count_at_slot(state, slot)
return compute_committee(
indices=get_active_validator_indices(state, epoch),
seed=get_seed(state, epoch, DOMAIN_BEACON_ATTESTER),
index=(slot % SLOTS_PER_EPOCH) * committees_per_slot + index,
count=committees_per_slot * SLOTS_PER_EPOCH,
)
get_beacon_proposer_index
def get_beacon_proposer_index(state: BeaconState) -> ValidatorIndex:
"""
Return the beacon proposer index at the current slot.
"""
epoch = get_current_epoch(state)
seed = hash(get_seed(state, epoch, DOMAIN_BEACON_PROPOSER) + int_to_bytes(state.slot, length=8))
indices = get_active_validator_indices(state, epoch)
return compute_proposer_index(state, indices, seed)
get_total_balance
def get_total_balance(state: BeaconState, indices: Set[ValidatorIndex]) -> Gwei:
"""
Return the combined effective balance of the ``indices``. (1 Gwei minimum to avoid divisions by zero.)
"""
return Gwei(max(1, sum([state.validators[index].effective_balance for index in indices])))
get_total_active_balance
def get_total_active_balance(state: BeaconState) -> Gwei:
"""
Return the combined effective balance of the active validators.
"""
return get_total_balance(state, set(get_active_validator_indices(state, get_current_epoch(state))))
get_domain
def get_domain(state: BeaconState, domain_type: DomainType, epoch: Epoch=None) -> Domain:
"""
Return the signature domain (fork version concatenated with domain type) of a message.
"""
epoch = get_current_epoch(state) if epoch is None else epoch
fork_version = state.fork.previous_version if epoch < state.fork.epoch else state.fork.current_version
return compute_domain(domain_type, fork_version)
get_indexed_attestation
def get_indexed_attestation(state: BeaconState, attestation: Attestation) -> IndexedAttestation:
"""
Return the indexed attestation corresponding to ``attestation``.
"""
attesting_indices = get_attesting_indices(state, attestation.data, attestation.aggregation_bits)
return IndexedAttestation(
attesting_indices=sorted(attesting_indices),
data=attestation.data,
signature=attestation.signature,
)
get_attesting_indices
def get_attesting_indices(state: BeaconState,
data: AttestationData,
bits: Bitlist[MAX_VALIDATORS_PER_COMMITTEE]) -> Set[ValidatorIndex]:
"""
Return the set of attesting indices corresponding to ``data`` and ``bits``.
"""
committee = get_beacon_committee(state, data.slot, data.index)
return set(index for i, index in enumerate(committee) if bits[i])
Beacon state mutators
increase_balance
def increase_balance(state: BeaconState, index: ValidatorIndex, delta: Gwei) -> None:
"""
Increase the validator balance at index ``index`` by ``delta``.
"""
state.balances[index] += delta
decrease_balance
def decrease_balance(state: BeaconState, index: ValidatorIndex, delta: Gwei) -> None:
"""
Decrease the validator balance at index ``index`` by ``delta``, with underflow protection.
"""
state.balances[index] = 0 if delta > state.balances[index] else state.balances[index] - delta
initiate_validator_exit
def initiate_validator_exit(state: BeaconState, index: ValidatorIndex) -> None:
"""
Initiate the exit of the validator with index ``index``.
"""
# Return if validator already initiated exit
validator = state.validators[index]
if validator.exit_epoch != FAR_FUTURE_EPOCH:
return
# Compute exit queue epoch
exit_epochs = [v.exit_epoch for v in state.validators if v.exit_epoch != FAR_FUTURE_EPOCH]
exit_queue_epoch = max(exit_epochs + [compute_activation_exit_epoch(get_current_epoch(state))])
exit_queue_churn = len([v for v in state.validators if v.exit_epoch == exit_queue_epoch])
if exit_queue_churn >= get_validator_churn_limit(state):
exit_queue_epoch += Epoch(1)
# Set validator exit epoch and withdrawable epoch
validator.exit_epoch = exit_queue_epoch
validator.withdrawable_epoch = Epoch(validator.exit_epoch + MIN_VALIDATOR_WITHDRAWABILITY_DELAY)
slash_validator
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)
# 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, whistleblower_reward - proposer_reward)
Genesis
Before the Ethereum 2.0 genesis has been triggered, and for every Ethereum 1.0 block, let candidate_state = initialize_beacon_state_from_eth1(eth1_block_hash, eth1_timestamp, deposits)
where:
eth1_block_hash
is the hash of the Ethereum 1.0 blocketh1_timestamp
is the Unix timestamp corresponding toeth1_block_hash
deposits
is the sequence of all deposits, ordered chronologically, up to (and including) the block with hasheth1_block_hash
def initialize_beacon_state_from_eth1(eth1_block_hash: Bytes32,
eth1_timestamp: uint64,
deposits: Sequence[Deposit]) -> BeaconState:
fork = Fork(
previous_version=GENESIS_FORK_VERSION,
current_version=GENESIS_FORK_VERSION,
epoch=GENESIS_EPOCH,
)
state = BeaconState(
genesis_time=eth1_timestamp - eth1_timestamp % MIN_GENESIS_DELAY + 2 * MIN_GENESIS_DELAY,
fork=fork,
eth1_data=Eth1Data(block_hash=eth1_block_hash, deposit_count=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
return state
Genesis state
Let genesis_state = candidate_state
whenever is_valid_genesis_state(candidate_state) is True
for the first time.
def is_valid_genesis_state(state: BeaconState) -> bool:
if state.genesis_time < MIN_GENESIS_TIME:
return False
if len(get_active_validator_indices(state, GENESIS_EPOCH)) < MIN_GENESIS_ACTIVE_VALIDATOR_COUNT:
return False
return True
Note: The is_valid_genesis_state
function (including MIN_GENESIS_TIME
and MIN_GENESIS_ACTIVE_VALIDATOR_COUNT
) is a placeholder for testing. It has yet to be finalized by the community, and can be updated as necessary.
Genesis block
Let genesis_block = BeaconBlock(state_root=hash_tree_root(genesis_state))
.
Beacon chain state transition function
The post-state corresponding to a pre-state state
and a signed block signed_block
is defined as state_transition(state, signed_block)
. State transitions that trigger an unhandled exception (e.g. a failed assert
or an out-of-range list access) are considered invalid.
def state_transition(state: BeaconState, signed_block: SignedBeaconBlock, validate_result: bool=True) -> BeaconState:
block = signed_block.message
# Process slots (including those with no blocks) since block
process_slots(state, block.slot)
# Verify signature
if validate_result:
assert verify_block_signature(state, signed_block)
# Process block
process_block(state, block)
# Verify state root
if validate_result:
assert block.state_root == hash_tree_root(state)
# Return post-state
return state
def verify_block_signature(state: BeaconState, signed_block: SignedBeaconBlock) -> bool:
proposer = state.validators[get_beacon_proposer_index(state)]
signing_root = compute_signing_root(signed_block.message, get_domain(state, DOMAIN_BEACON_PROPOSER))
return bls.Verify(proposer.pubkey, signing_root, signed_block.signature)
def process_slots(state: BeaconState, slot: Slot) -> None:
assert state.slot <= slot
while state.slot < slot:
process_slot(state)
# Process epoch on the start slot of the next epoch
if (state.slot + 1) % SLOTS_PER_EPOCH == 0:
process_epoch(state)
state.slot += Slot(1)
def process_slot(state: BeaconState) -> None:
# Cache state root
previous_state_root = hash_tree_root(state)
state.state_roots[state.slot % SLOTS_PER_HISTORICAL_ROOT] = previous_state_root
# Cache latest block header state root
if state.latest_block_header.state_root == Bytes32():
state.latest_block_header.state_root = previous_state_root
# Cache block root
previous_block_root = hash_tree_root(state.latest_block_header)
state.block_roots[state.slot % SLOTS_PER_HISTORICAL_ROOT] = previous_block_root
Epoch processing
def process_epoch(state: BeaconState) -> None:
process_justification_and_finalization(state)
process_rewards_and_penalties(state)
process_registry_updates(state)
process_slashings(state)
process_final_updates(state)
Helper functions
def get_matching_source_attestations(state: BeaconState, epoch: Epoch) -> Sequence[PendingAttestation]:
assert epoch in (get_previous_epoch(state), get_current_epoch(state))
return state.current_epoch_attestations if epoch == get_current_epoch(state) else state.previous_epoch_attestations
def get_matching_target_attestations(state: BeaconState, epoch: Epoch) -> Sequence[PendingAttestation]:
return [
a for a in get_matching_source_attestations(state, epoch)
if a.data.target.root == get_block_root(state, epoch)
]
def get_matching_head_attestations(state: BeaconState, epoch: Epoch) -> Sequence[PendingAttestation]:
return [
a for a in get_matching_source_attestations(state, epoch)
if a.data.beacon_block_root == get_block_root_at_slot(state, a.data.slot)
]
def get_unslashed_attesting_indices(state: BeaconState,
attestations: Sequence[PendingAttestation]) -> Set[ValidatorIndex]:
output = set() # type: Set[ValidatorIndex]
for a in attestations:
output = output.union(get_attesting_indices(state, a.data, a.aggregation_bits))
return set(filter(lambda index: not state.validators[index].slashed, output))
def get_attesting_balance(state: BeaconState, attestations: Sequence[PendingAttestation]) -> Gwei:
return get_total_balance(state, get_unslashed_attesting_indices(state, attestations))
Justification and finalization
def process_justification_and_finalization(state: BeaconState) -> None:
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[:-1]
state.justification_bits[0] = 0b0
matching_target_attestations = get_matching_target_attestations(state, previous_epoch) # Previous epoch
if get_attesting_balance(state, matching_target_attestations) * 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_attestations = get_matching_target_attestations(state, current_epoch) # Current epoch
if get_attesting_balance(state, matching_target_attestations) * 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
Rewards and penalties
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) // BASE_REWARDS_PER_EPOCH)
def get_attestation_deltas(state: BeaconState) -> Tuple[Sequence[Gwei], Sequence[Gwei]]:
previous_epoch = get_previous_epoch(state)
total_balance = get_total_active_balance(state)
rewards = [Gwei(0) for _ in range(len(state.validators))]
penalties = [Gwei(0) for _ in range(len(state.validators))]
eligible_validator_indices = [
ValidatorIndex(index) for index, v in enumerate(state.validators)
if is_active_validator(v, previous_epoch) or (v.slashed and previous_epoch + 1 < v.withdrawable_epoch)
]
# Micro-incentives for matching FFG source, FFG target, and head
matching_source_attestations = get_matching_source_attestations(state, previous_epoch)
matching_target_attestations = get_matching_target_attestations(state, previous_epoch)
matching_head_attestations = get_matching_head_attestations(state, previous_epoch)
for attestations in (matching_source_attestations, matching_target_attestations, matching_head_attestations):
unslashed_attesting_indices = get_unslashed_attesting_indices(state, attestations)
attesting_balance = get_total_balance(state, unslashed_attesting_indices)
for index in eligible_validator_indices:
if index in unslashed_attesting_indices:
rewards[index] += get_base_reward(state, index) * attesting_balance // total_balance
else:
penalties[index] += get_base_reward(state, index)
# Proposer and inclusion delay micro-rewards
for index in get_unslashed_attesting_indices(state, matching_source_attestations):
attestation = min([
a for a in matching_source_attestations
if index in get_attesting_indices(state, a.data, a.aggregation_bits)
], key=lambda a: a.inclusion_delay)
proposer_reward = Gwei(get_base_reward(state, index) // PROPOSER_REWARD_QUOTIENT)
rewards[attestation.proposer_index] += proposer_reward
max_attester_reward = get_base_reward(state, index) - proposer_reward
rewards[index] += Gwei(max_attester_reward // attestation.inclusion_delay)
# Inactivity penalty
finality_delay = previous_epoch - state.finalized_checkpoint.epoch
if finality_delay > MIN_EPOCHS_TO_INACTIVITY_PENALTY:
matching_target_attesting_indices = get_unslashed_attesting_indices(state, matching_target_attestations)
for index in eligible_validator_indices:
penalties[index] += Gwei(BASE_REWARDS_PER_EPOCH * get_base_reward(state, index))
if index not in matching_target_attesting_indices:
effective_balance = state.validators[index].effective_balance
penalties[index] += Gwei(effective_balance * finality_delay // INACTIVITY_PENALTY_QUOTIENT)
return rewards, penalties
def process_rewards_and_penalties(state: BeaconState) -> None:
if get_current_epoch(state) == GENESIS_EPOCH:
return
rewards, penalties = get_attestation_deltas(state)
for index in range(len(state.validators)):
increase_balance(state, ValidatorIndex(index), rewards[index])
decrease_balance(state, ValidatorIndex(index), penalties[index])
Registry updates
def process_registry_updates(state: BeaconState) -> None:
# Process activation eligibility and ejections
for index, validator in enumerate(state.validators):
if is_eligible_for_activation_queue(validator):
validator.activation_eligibility_epoch = get_current_epoch(state) + 1
if is_active_validator(validator, get_current_epoch(state)) and validator.effective_balance <= EJECTION_BALANCE:
initiate_validator_exit(state, ValidatorIndex(index))
# Queue validators eligible for activation and not yet dequeued for activation
activation_queue = sorted([
index for index, validator in enumerate(state.validators)
if is_eligible_for_activation(state, validator)
# Order by the sequence of activation_eligibility_epoch setting and then index
], key=lambda index: (state.validators[index].activation_eligibility_epoch, index))
# Dequeued validators for activation up to churn limit
for index in activation_queue[:get_validator_churn_limit(state)]:
validator = state.validators[index]
validator.activation_epoch = compute_activation_exit_epoch(get_current_epoch(state))
Slashings
def process_slashings(state: BeaconState) -> None:
epoch = get_current_epoch(state)
total_balance = get_total_active_balance(state)
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 * min(sum(state.slashings) * 3, total_balance)
penalty = penalty_numerator // total_balance * increment
decrease_balance(state, ValidatorIndex(index), penalty)
Final updates
def process_final_updates(state: BeaconState) -> None:
current_epoch = get_current_epoch(state)
next_epoch = Epoch(current_epoch + 1)
# Reset eth1 data votes
if next_epoch % EPOCHS_PER_ETH1_VOTING_PERIOD == 0:
state.eth1_data_votes = []
# Update effective balances with hysteresis
for index, validator in enumerate(state.validators):
balance = state.balances[index]
HALF_INCREMENT = EFFECTIVE_BALANCE_INCREMENT // 2
if balance < validator.effective_balance or validator.effective_balance + 3 * HALF_INCREMENT < balance:
validator.effective_balance = min(balance - balance % EFFECTIVE_BALANCE_INCREMENT, MAX_EFFECTIVE_BALANCE)
# Reset slashings
state.slashings[next_epoch % EPOCHS_PER_SLASHINGS_VECTOR] = Gwei(0)
# Set randao mix
state.randao_mixes[next_epoch % EPOCHS_PER_HISTORICAL_VECTOR] = get_randao_mix(state, current_epoch)
# Set historical root accumulator
if next_epoch % (SLOTS_PER_HISTORICAL_ROOT // SLOTS_PER_EPOCH) == 0:
historical_batch = HistoricalBatch(block_roots=state.block_roots, state_roots=state.state_roots)
state.historical_roots.append(hash_tree_root(historical_batch))
# Rotate current/previous epoch attestations
state.previous_epoch_attestations = state.current_epoch_attestations
state.current_epoch_attestations = []
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)
Block header
def process_block_header(state: BeaconState, block: BeaconBlock) -> None:
# Verify that the slots match
assert block.slot == state.slot
# Verify that the parent matches
assert block.parent_root == hash_tree_root(state.latest_block_header)
# Cache current block as the new latest block
state.latest_block_header = BeaconBlockHeader(
slot=block.slot,
parent_root=block.parent_root,
state_root=Bytes32(), # Overwritten in the next process_slot call
body_root=hash_tree_root(block.body),
)
# Verify proposer is not slashed
proposer = state.validators[get_beacon_proposer_index(state)]
assert not proposer.slashed
RANDAO
def process_randao(state: BeaconState, body: BeaconBlockBody) -> None:
epoch = get_current_epoch(state)
# Verify RANDAO reveal
proposer = state.validators[get_beacon_proposer_index(state)]
signing_root = compute_signing_root(epoch, get_domain(state, DOMAIN_RANDAO))
assert bls.Verify(proposer.pubkey, signing_root, body.randao_reveal)
# Mix in RANDAO reveal
mix = xor(get_randao_mix(state, epoch), hash(body.randao_reveal))
state.randao_mixes[epoch % EPOCHS_PER_HISTORICAL_VECTOR] = mix
Eth1 data
def process_eth1_data(state: BeaconState, body: BeaconBlockBody) -> None:
state.eth1_data_votes.append(body.eth1_data)
if state.eth1_data_votes.count(body.eth1_data) * 2 > EPOCHS_PER_ETH1_VOTING_PERIOD * SLOTS_PER_EPOCH:
state.eth1_data = body.eth1_data
Operations
def process_operations(state: BeaconState, body: BeaconBlockBody) -> None:
# Verify that outstanding deposits are processed up to the maximum number of deposits
assert len(body.deposits) == min(MAX_DEPOSITS, state.eth1_data.deposit_count - state.eth1_deposit_index)
def for_ops(operations: Sequence[Any], fn: Callable[[BeaconState, Any], None]) -> None:
for operation in operations:
fn(state, operation)
for_ops(body.proposer_slashings, process_proposer_slashing)
for_ops(body.attester_slashings, process_attester_slashing)
for_ops(body.attestations, process_attestation)
for_ops(body.deposits, process_deposit)
for_ops(body.voluntary_exits, process_voluntary_exit)
Proposer slashings
def process_proposer_slashing(state: BeaconState, proposer_slashing: ProposerSlashing) -> None:
# Verify header slots match
assert proposer_slashing.signed_header_1.message.slot == proposer_slashing.signed_header_2.message.slot
# Verify the headers are different
assert proposer_slashing.signed_header_1 != proposer_slashing.signed_header_2
# Verify the proposer is slashable
proposer = state.validators[proposer_slashing.proposer_index]
assert is_slashable_validator(proposer, get_current_epoch(state))
# Verify signatures
for signed_header in (proposer_slashing.signed_header_1, proposer_slashing.signed_header_2):
domain = get_domain(state, DOMAIN_BEACON_PROPOSER, compute_epoch_at_slot(signed_header.message.slot))
signing_root = compute_signing_root(signed_header.message, domain)
assert bls.Verify(proposer.pubkey, signing_root, signed_header.signature)
slash_validator(state, proposer_slashing.proposer_index)
Attester slashings
def process_attester_slashing(state: BeaconState, attester_slashing: AttesterSlashing) -> None:
attestation_1 = attester_slashing.attestation_1
attestation_2 = attester_slashing.attestation_2
assert is_slashable_attestation_data(attestation_1.data, attestation_2.data)
assert is_valid_indexed_attestation(state, attestation_1)
assert is_valid_indexed_attestation(state, attestation_2)
slashed_any = False
indices = set(attestation_1.attesting_indices).intersection(attestation_2.attesting_indices)
for index in sorted(indices):
if is_slashable_validator(state.validators[index], get_current_epoch(state)):
slash_validator(state, index)
slashed_any = True
assert slashed_any
Attestations
def process_attestation(state: BeaconState, attestation: Attestation) -> None:
data = attestation.data
assert data.index < get_committee_count_at_slot(state, data.slot)
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
committee = get_beacon_committee(state, data.slot, data.index)
assert len(attestation.aggregation_bits) == len(committee)
pending_attestation = PendingAttestation(
data=data,
aggregation_bits=attestation.aggregation_bits,
inclusion_delay=state.slot - data.slot,
proposer_index=get_beacon_proposer_index(state),
)
if data.target.epoch == get_current_epoch(state):
assert data.source == state.current_justified_checkpoint
state.current_epoch_attestations.append(pending_attestation)
else:
assert data.source == state.previous_justified_checkpoint
state.previous_epoch_attestations.append(pending_attestation)
# Verify signature
assert is_valid_indexed_attestation(state, get_indexed_attestation(state, attestation))
Deposits
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 = [v.pubkey for v 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)
if not bls.Verify(pubkey, signing_root, deposit.data.signature):
return
# Add validator and balance entries
state.validators.append(Validator(
pubkey=pubkey,
withdrawal_credentials=deposit.data.withdrawal_credentials,
activation_eligibility_epoch=FAR_FUTURE_EPOCH,
activation_epoch=FAR_FUTURE_EPOCH,
exit_epoch=FAR_FUTURE_EPOCH,
withdrawable_epoch=FAR_FUTURE_EPOCH,
effective_balance=min(amount - amount % EFFECTIVE_BALANCE_INCREMENT, MAX_EFFECTIVE_BALANCE),
))
state.balances.append(amount)
else:
# Increase balance by deposit amount
index = ValidatorIndex(validator_pubkeys.index(pubkey))
increase_balance(state, index, amount)
Voluntary exits
def process_voluntary_exit(state: BeaconState, signed_voluntary_exit: SignedVoluntaryExit) -> None:
voluntary_exit = signed_voluntary_exit.message
validator = state.validators[voluntary_exit.validator_index]
# Verify the validator is active
assert is_active_validator(validator, get_current_epoch(state))
# Verify exit has not been initiated
assert validator.exit_epoch == FAR_FUTURE_EPOCH
# Exits must specify an epoch when they become valid; they are not valid before then
assert get_current_epoch(state) >= voluntary_exit.epoch
# Verify the validator has been active long enough
assert get_current_epoch(state) >= validator.activation_epoch + PERSISTENT_COMMITTEE_PERIOD
# Verify signature
domain = get_domain(state, DOMAIN_VOLUNTARY_EXIT, voluntary_exit.epoch)
signing_root = compute_signing_root(voluntary_exit, domain)
assert bls.Verify(validator.pubkey, signing_root, signed_voluntary_exit.signature)
# Initiate exit
initiate_validator_exit(state, voluntary_exit.validator_index)