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Merge pull request #1525 from ethereum/JustinDrake-patch-2
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Minor cosmetic cleanups
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@djrtwo
djrtwo authored Jan 8, 2020
2 parents 38f947b + f01254d commit ac33b3d
Showing 1 changed file with 31 additions and 33 deletions.
64 changes: 31 additions & 33 deletions specs/core/0_beacon-chain.md
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Original file line number Diff line number Diff line change
Expand Up @@ -212,11 +212,11 @@ The following values are (non-configurable) constants used throughout the specif
| `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 |
| `SLOTS_PER_ETH1_VOTING_PERIOD` | `2**10` (= 1,024) | slots | ~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 |
| `MIN_EPOCHS_TO_INACTIVITY_PENALTY` | `2**2` (= 4) | epochs | 25.6 minutes |

### State list lengths

Expand All @@ -225,7 +225,7 @@ The following values are (non-configurable) constants used throughout the specif
| `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 | ~26,131 years |
| `VALIDATOR_REGISTRY_LIMIT` | `2**40` (= 1,099,511,627,776) | validator spots |
| `VALIDATOR_REGISTRY_LIMIT` | `2**40` (= 1,099,511,627,776) | validators |

### Rewards and penalties

Expand Down Expand Up @@ -366,7 +366,7 @@ class DepositData(Container):
pubkey: BLSPubkey
withdrawal_credentials: Bytes32
amount: Gwei
signature: BLSSignature # signing over DepositMessage
signature: BLSSignature # Signing over DepositMessage
```

#### `BeaconBlockHeader`
Expand Down Expand Up @@ -419,7 +419,7 @@ class Attestation(Container):

```python
class Deposit(Container):
proof: Vector[Bytes32, DEPOSIT_CONTRACT_TREE_DEPTH + 1] # Merkle path to deposit data list root
proof: Vector[Bytes32, DEPOSIT_CONTRACT_TREE_DEPTH + 1] # Merkle path to deposit root
data: DepositData
```

Expand Down Expand Up @@ -496,8 +496,6 @@ class BeaconState(Container):

### Signed envelopes

Some messages in the protocol are wrapped in an envelope to better facilitate adding/pruning the signature and to `hash_tree_root` the `message` separate from the signature.

#### `SignedVoluntaryExit`

```python
Expand Down Expand Up @@ -1038,7 +1036,7 @@ def initiate_validator_exit(state: BeaconState, index: ValidatorIndex) -> None:

# 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_epoch = max(exit_epochs, default=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)
Expand Down Expand Up @@ -1139,19 +1137,21 @@ 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 block `block` is defined as `state_transition(state, block)`. State transitions that trigger an unhandled exception (e.g. a failed `assert` or an out-of-range list access) are considered invalid.
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.

```python
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, signed_block.message.slot)
process_slots(state, block.slot)
# Verify signature
if validate_result:
assert verify_block_signature(state, signed_block)
# Process block
process_block(state, signed_block.message)
process_block(state, block)
# Verify state root
if validate_result:
assert signed_block.message.state_root == hash_tree_root(state) # Validate state root
assert block.state_root == hash_tree_root(state)
# Return post-state
return state
```
Expand Down Expand Up @@ -1327,9 +1327,7 @@ def get_attestation_deltas(state: BeaconState) -> Tuple[Sequence[Gwei], Sequence
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
)
rewards[index] += Gwei(max_attester_reward // attestation.inclusion_delay)

# Inactivity penalty
finality_delay = previous_epoch - state.finalized_checkpoint.epoch
Expand All @@ -1338,9 +1336,8 @@ def get_attestation_deltas(state: BeaconState) -> Tuple[Sequence[Gwei], Sequence
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:
penalties[index] += Gwei(
state.validators[index].effective_balance * finality_delay // INACTIVITY_PENALTY_QUOTIENT
)
effective_balance = state.validators[index].effective_balance
penalties[index] += Gwei(effective_balance * finality_delay // INACTIVITY_PENALTY_QUOTIENT)

return rewards, penalties
```
Expand Down Expand Up @@ -1440,13 +1437,14 @@ def process_block_header(state: BeaconState, block: BeaconBlock) -> None:
assert block.slot == state.slot
# Verify that the parent matches
assert block.parent_root == hash_tree_root(state.latest_block_header)
# Save current block as the new latest block
# Cache current block as the new latest block
state.latest_block_header = BeaconBlockHeader(
slot=block.slot,
parent_root=block.parent_root,
# `state_root` is zeroed and overwritten in the next `process_slot` call
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
Expand Down Expand Up @@ -1498,14 +1496,14 @@ def process_operations(state: BeaconState, body: BeaconBlockBody) -> None:

```python
def process_proposer_slashing(state: BeaconState, proposer_slashing: ProposerSlashing) -> None:
proposer = state.validators[proposer_slashing.proposer_index]
# Verify slots match
# Verify header slots match
assert proposer_slashing.signed_header_1.message.slot == proposer_slashing.signed_header_2.message.slot
# But the headers are different
assert proposer_slashing.signed_header_1.message != proposer_slashing.signed_header_2.message
# Check proposer is slashable
# 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))
# Signatures are valid
# 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)
Expand Down Expand Up @@ -1560,7 +1558,7 @@ def process_attestation(state: BeaconState, attestation: Attestation) -> None:
assert data.source == state.previous_justified_checkpoint
state.previous_epoch_attestations.append(pending_attestation)

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

Expand All @@ -1572,7 +1570,7 @@ def process_deposit(state: BeaconState, deposit: Deposit) -> None:
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
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,
)
Expand All @@ -1584,14 +1582,14 @@ def process_deposit(state: BeaconState, deposit: Deposit) -> None:
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) for new validators.
# Note: The deposit contract does not check signatures.
# Note: Deposits are valid across forks, thus the deposit domain is retrieved directly from `compute_domain`.
# 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)
signing_root = compute_signing_root(deposit_message, compute_domain(DOMAIN_DEPOSIT))
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

Expand Down Expand Up @@ -1620,7 +1618,7 @@ def process_voluntary_exit(state: BeaconState, signed_voluntary_exit: SignedVolu
validator = state.validators[voluntary_exit.validator_index]
# Verify the validator is active
assert is_active_validator(validator, get_current_epoch(state))
# Verify the validator has not yet exited
# 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
Expand Down

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