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Unified equivocation slashing #1737

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Unified equivocation slashing #1737

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22a5ba4
Unified equivocation slashing
JustinDrake Apr 21, 2020
a899157
Update beacon-chain.md
JustinDrake Apr 21, 2020
0a683df
Update beacon-chain.md
JustinDrake Apr 21, 2020
82bda04
Update beacon-chain.md
JustinDrake Apr 21, 2020
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123 changes: 58 additions & 65 deletions specs/phase0/beacon-chain.md
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Original file line number Diff line number Diff line change
Expand Up @@ -7,7 +7,6 @@
<!-- START doctoc generated TOC please keep comment here to allow auto update -->
<!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE -->


- [Introduction](#introduction)
- [Notation](#notation)
- [Custom types](#custom-types)
Expand All @@ -34,23 +33,22 @@
- [`HistoricalBatch`](#historicalbatch)
- [`DepositMessage`](#depositmessage)
- [`DepositData`](#depositdata)
- [`BeaconBlockHeader`](#beaconblockheader)
- [`SigningRoot`](#signingroot)
- [`SigningData`](#signingdata)
- [Beacon operations](#beacon-operations)
- [`ProposerSlashing`](#proposerslashing)
- [`Equivocation`](#equivocation)
- [`AttesterSlashing`](#attesterslashing)
- [`Attestation`](#attestation)
- [`Deposit`](#deposit)
- [`VoluntaryExit`](#voluntaryexit)
- [Beacon blocks](#beacon-blocks)
- [`BeaconBlockHeader`](#beaconblockheader)
- [`BeaconBlockBody`](#beaconblockbody)
- [`BeaconBlock`](#beaconblock)
- [Beacon state](#beacon-state)
- [`BeaconState`](#beaconstate)
- [Signed envelopes](#signed-envelopes)
- [`SignedVoluntaryExit`](#signedvoluntaryexit)
- [`SignedBeaconBlock`](#signedbeaconblock)
- [`SignedBeaconBlockHeader`](#signedbeaconblockheader)
- [Helper functions](#helper-functions)
- [Math](#math)
- [`integer_squareroot`](#integer_squareroot)
Expand Down Expand Up @@ -118,7 +116,7 @@
- [RANDAO](#randao)
- [Eth1 data](#eth1-data)
- [Operations](#operations)
- [Proposer slashings](#proposer-slashings)
- [Equivocations](#equivocations)
- [Attester slashings](#attester-slashings)
- [Attestations](#attestations)
- [Deposits](#deposits)
Expand Down Expand Up @@ -191,7 +189,6 @@ The following values are (non-configurable) constants used throughout the specif
| `HYSTERESIS_DOWNWARD_MULTIPLIER` | `1` |
| `HYSTERESIS_UPWARD_MULTIPLIER` | `5` |


- For the safety of committees, `TARGET_COMMITTEE_SIZE` exceeds [the recommended minimum committee size of 111](http://web.archive.org/web/20190504131341/https://vitalik.ca/files/Ithaca201807_Sharding.pdf); with sufficient active validators (at least `SLOTS_PER_EPOCH * TARGET_COMMITTEE_SIZE`), the shuffling algorithm ensures committee sizes of at least `TARGET_COMMITTEE_SIZE`. (Unbiasable randomness with a Verifiable Delay Function (VDF) will improve committee robustness and lower the safe minimum committee size.)

### Gwei values
Expand Down Expand Up @@ -251,7 +248,7 @@ The following values are (non-configurable) constants used throughout the specif

| Name | Value |
| - | - |
| `MAX_PROPOSER_SLASHINGS` | `2**4` (= 16) |
| `MAX_EQUIVOCATIONS` | `2**4` (= 16) |
| `MAX_ATTESTER_SLASHINGS` | `2**0` (= 1) |
| `MAX_ATTESTATIONS` | `2**7` (= 128) |
| `MAX_DEPOSITS` | `2**4` (= 16) |
Expand All @@ -269,7 +266,6 @@ The following values are (non-configurable) constants used throughout the specif
| `DOMAIN_SELECTION_PROOF` | `DomainType('0x05000000')` |
| `DOMAIN_AGGREGATE_AND_PROOF` | `DomainType('0x06000000')` |


## Containers

The following types are [SimpleSerialize (SSZ)](../../ssz/simple-serialize.md) containers.
Expand Down Expand Up @@ -388,33 +384,28 @@ class DepositData(Container):
signature: BLSSignature # Signing over DepositMessage
```

#### `BeaconBlockHeader`

```python
class BeaconBlockHeader(Container):
slot: Slot
proposer_index: ValidatorIndex
parent_root: Root
state_root: Root
body_root: Root
```

#### `SigningRoot`
#### `SigningData`

```python
class SigningRoot(Container):
class SigningData(Container):
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object_root: Root
equivocation_root: Root
domain: Domain
```

### Beacon operations

#### `ProposerSlashing`
#### `Equivocation`

```python
class ProposerSlashing(Container):
signed_header_1: SignedBeaconBlockHeader
signed_header_2: SignedBeaconBlockHeader
class Equivocation(Container):
validator_index: ValidatorIndex
domain: Domain
equivocation_root: Root
object_root_1: Root
object_root_2: Root
signature_1: BLSSignature
signature_2: BLSSignature
```

#### `AttesterSlashing`
Expand Down Expand Up @@ -452,6 +443,17 @@ class VoluntaryExit(Container):

### Beacon blocks

#### `BeaconBlockHeader`

```python
class BeaconBlockHeader(Container):
slot: Slot
proposer_index: ValidatorIndex
parent_root: Root
state_root: Root
body_root: Root
```

#### `BeaconBlockBody`

```python
Expand All @@ -460,7 +462,7 @@ class BeaconBlockBody(Container):
eth1_data: Eth1Data # Eth1 data vote
graffiti: Bytes32 # Arbitrary data
# Operations
proposer_slashings: List[ProposerSlashing, MAX_PROPOSER_SLASHINGS]
equivocations: List[Equivocation, MAX_EQUIVOCATIONS]
attester_slashings: List[AttesterSlashing, MAX_ATTESTER_SLASHINGS]
attestations: List[Attestation, MAX_ATTESTATIONS]
deposits: List[Deposit, MAX_DEPOSITS]
Expand Down Expand Up @@ -533,14 +535,6 @@ class SignedBeaconBlock(Container):
signature: BLSSignature
```

#### `SignedBeaconBlockHeader`

```python
class SignedBeaconBlockHeader(Container):
message: BeaconBlockHeader
signature: BLSSignature
```

## Helper functions

*Note*: The definitions below are for specification purposes and are not necessarily optimal implementations.
Expand Down Expand Up @@ -850,15 +844,15 @@ def compute_domain(domain_type: DomainType, fork_version: Version=None, genesis_
#### `compute_signing_root`

```python
def compute_signing_root(ssz_object: SSZObject, domain: Domain) -> Root:
def compute_signing_root(ssz_object: SSZObject, domain: Domain, equivocation_root: Root=Root()) -> Root:
"""
Return the signing root of an object by calculating the root of the object-domain tree.
Return the signing root corresponding to the signing data.
"""
domain_wrapped_object = SigningRoot(
return hash_tree_root(SigningData(
object_root=hash_tree_root(ssz_object),
equivocation_root=equivocation_root,
domain=domain,
)
return hash_tree_root(domain_wrapped_object)
))
```

### Beacon state accessors
Expand Down Expand Up @@ -1217,7 +1211,9 @@ def state_transition(state: BeaconState, signed_block: SignedBeaconBlock, valida
```python
def verify_block_signature(state: BeaconState, signed_block: SignedBeaconBlock) -> bool:
proposer = state.validators[signed_block.message.proposer_index]
signing_root = compute_signing_root(signed_block.message, get_domain(state, DOMAIN_BEACON_PROPOSER))
domain = get_domain(state, DOMAIN_BEACON_PROPOSER)
equivocation_root = hash_tree_root(Slot(signed_block.slot))
signing_root = compute_signing_root(signed_block.message, domain, equivocation_root)
return bls.Verify(proposer.pubkey, signing_root, signed_block.signature)
```

Expand Down Expand Up @@ -1550,36 +1546,33 @@ def process_operations(state: BeaconState, body: BeaconBlockBody) -> None:
for operation in operations:
fn(state, operation)

for_ops(body.proposer_slashings, process_proposer_slashing)
for_ops(body.equivocations, process_equivocation)
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

```python
def process_proposer_slashing(state: BeaconState, proposer_slashing: ProposerSlashing) -> None:
header_1 = proposer_slashing.signed_header_1.message
header_2 = proposer_slashing.signed_header_2.message

# Verify header slots match
assert header_1.slot == header_2.slot
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# Verify header proposer indices match
assert header_1.proposer_index == header_2.proposer_index
# Verify the headers are different
assert header_1 != header_2
# Verify the proposer is slashable
proposer = state.validators[header_1.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, header_1.proposer_index)
##### Equivocations

```python
def process_equivocation(state: BeaconState, equivocation: Equivocation) -> None:
# Verify that the domain is eligible for equivocation slashing
assert equivocation.domain in (DOMAIN_BEACON_PROPOSER)
# Verify that the equivocation root is not all zero bytes
assert equivocation.equivocation_root != Root()
# Verify that the signing roots are distinct
signing_root_1 = hash_tree_root(SigningData(equivocation.object_root_1, equivocation_root, domain))
signing_root_2 = hash_tree_root(SigningData(equivocation.object_root_2, equivocation_root, domain))
assert signing_root_1 != signing_root_2
# Verify that the signatures are valid
validator = state.validators[equivocation.validator_index]
assert bls.Verify(validator.pubkey, signing_root_1, equivocation.signature_1)
assert bls.Verify(validator.pubkey, signing_root_2, equivocation.signature_2)
# Verify that the validator is slashable
assert is_slashable_validator(validator, get_current_epoch(state))
# Slash validator
slash_validator(state, equivocation.validator_index)
```

##### Attester slashings
Expand Down