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Merge pull request #633 from ethereum/JustinDrake-patch-1
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Refactor signature handling
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@djrtwo
djrtwo committed Feb 18, 2019
2 parents 5fbbb4f + 9eb3be5 commit 9dcc6b8
Showing 1 changed file with 48 additions and 88 deletions.
136 changes: 48 additions & 88 deletions specs/core/0_beacon-chain.md
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Original file line number Diff line number Diff line change
Expand Up @@ -43,7 +43,7 @@
- [Beacon chain blocks](#beacon-chain-blocks)
- [`BeaconBlock`](#beaconblock)
- [`BeaconBlockBody`](#beaconblockbody)
- [`ProposalSignedData`](#proposalsigneddata)
- [`Proposal`](#proposal)
- [Beacon chain state](#beacon-chain-state)
- [`BeaconState`](#beaconstate)
- [`Validator`](#validator)
Expand Down Expand Up @@ -94,7 +94,6 @@
- [`bls_verify`](#bls_verify)
- [`bls_verify_multiple`](#bls_verify_multiple)
- [`bls_aggregate_pubkeys`](#bls_aggregate_pubkeys)
- [`validate_proof_of_possession`](#validate_proof_of_possession)
- [`process_deposit`](#process_deposit)
- [Routines for updating validator status](#routines-for-updating-validator-status)
- [`activate_validator`](#activate_validator)
Expand All @@ -117,7 +116,7 @@
- [Block roots](#block-roots)
- [Per-block processing](#per-block-processing)
- [Slot](#slot-1)
- [Proposer signature](#proposer-signature)
- [Block signature](#block-signature)
- [RANDAO](#randao)
- [Eth1 data](#eth1-data)
- [Transactions](#transactions)
Expand Down Expand Up @@ -299,14 +298,10 @@ The following data structures are defined as [SimpleSerialize (SSZ)](https://git
{
# Proposer index
'proposer_index': 'uint64',
# First proposal data
'proposal_data_1': ProposalSignedData,
# First proposal signature
'proposal_signature_1': 'bytes96',
# Second proposal data
'proposal_data_2': ProposalSignedData,
# Second proposal signature
'proposal_signature_2': 'bytes96',
# First proposal
'proposal_1': Proposal,
# Second proposal
'proposal_2': Proposal,
}
```

Expand Down Expand Up @@ -363,9 +358,9 @@ The following data structures are defined as [SimpleSerialize (SSZ)](https://git
'slot': 'uint64',
# Shard number
'shard': 'uint64',
# Hash of root of the signed beacon block
# Root of the signed beacon block
'beacon_block_root': 'bytes32',
# Hash of root of the ancestor at the epoch boundary
# Root of the ancestor at the epoch boundary
'epoch_boundary_root': 'bytes32',
# Shard block's hash of root
'shard_block_root': 'bytes32',
Expand Down Expand Up @@ -474,16 +469,17 @@ The following data structures are defined as [SimpleSerialize (SSZ)](https://git

```python
{
## Header ##
# Header
'slot': 'uint64',
'parent_root': 'bytes32',
'state_root': 'bytes32',
'randao_reveal': 'bytes96',
'eth1_data': Eth1Data,
'signature': 'bytes96',

## Body ##
# Body
'body': BeaconBlockBody,
# Signature
'signature': 'bytes96',
}
```

Expand All @@ -500,16 +496,18 @@ The following data structures are defined as [SimpleSerialize (SSZ)](https://git
}
```

#### `ProposalSignedData`
#### `Proposal`

```python
{
# Slot number
'slot': 'uint64',
# Shard number (`BEACON_CHAIN_SHARD_NUMBER` for beacon chain)
'shard': 'uint64',
# Block's hash of root
# Block root
'block_root': 'bytes32',
# Signature
'signature': 'bytes96',
}
```

Expand Down Expand Up @@ -670,6 +668,10 @@ Note: We aim to migrate to a S[T/N]ARK-friendly hash function in a future Ethere

`def hash_tree_root(object: SSZSerializable) -> Bytes32` is a function for hashing objects into a single root utilizing a hash tree structure. `hash_tree_root` is defined in the [SimpleSerialize spec](https://github.com/ethereum/eth2.0-specs/blob/master/specs/simple-serialize.md#tree-hash).

### `signed_root`

`def signed_root(object: SSZContainer) -> Bytes32` is a function defined in the [SimpleSerialize spec](https://github.com/ethereum/eth2.0-specs/blob/master/specs/simple-serialize.md#signed-roots) to compute signed messages.

### `slot_to_epoch`

```python
Expand Down Expand Up @@ -1241,60 +1243,33 @@ def get_entry_exit_effect_epoch(epoch: Epoch) -> Epoch:

`bls_aggregate_pubkeys` is a function for aggregating multiple BLS public keys into a single aggregate key, defined in the [BLS Signature spec](https://github.com/ethereum/eth2.0-specs/blob/master/specs/bls_signature.md#bls_aggregate_pubkeys).

### `validate_proof_of_possession`
### `process_deposit`

Used to add a [validator](#dfn-validator) or top up an existing [validator](#dfn-validator)'s balance by some `deposit` amount:

```python
def validate_proof_of_possession(state: BeaconState,
pubkey: BLSPubkey,
proof_of_possession: BLSSignature,
withdrawal_credentials: Bytes32) -> bool:
def process_deposit(state: BeaconState, deposit: Deposit) -> None:
"""
Verify the given ``proof_of_possession``.
Process a deposit from Ethereum 1.0.
Note that this function mutates ``state``.
"""
proof_of_possession_data = DepositInput(
pubkey=pubkey,
withdrawal_credentials=withdrawal_credentials,
proof_of_possession=EMPTY_SIGNATURE,
)
deposit_input = deposit.deposit_data.deposit_input

return bls_verify(
pubkey=pubkey,
message_hash=hash_tree_root(proof_of_possession_data),
signature=proof_of_possession,
assert bls_verify(
pubkey=deposit_input.pubkey,
message_hash=signed_root(deposit_input, "proof_of_possession"),
signature=deposit_input.proof_of_possession,
domain=get_domain(
state.fork,
get_current_epoch(state),
DOMAIN_DEPOSIT,
)
)
```

### `process_deposit`

Used to add a [validator](#dfn-validator) or top up an existing [validator](#dfn-validator)'s balance by some `deposit` amount:

```python
def process_deposit(state: BeaconState,
pubkey: BLSPubkey,
amount: Gwei,
proof_of_possession: BLSSignature,
withdrawal_credentials: Bytes32) -> None:
"""
Process a deposit from Ethereum 1.0.
Note that this function mutates ``state``.
"""
# Validate the given `proof_of_possession`
proof_is_valid = validate_proof_of_possession(
state,
pubkey,
proof_of_possession,
withdrawal_credentials,
)

if not proof_is_valid:
return

validator_pubkeys = [v.pubkey for v in state.validator_registry]
pubkey = deposit_input.pubkey
amount = deposit.deposit_data.amount
withdrawal_credentials = deposit_input.withdrawal_credentials

if pubkey not in validator_pubkeys:
# Add new validator
Expand Down Expand Up @@ -1521,13 +1496,7 @@ def get_genesis_beacon_state(genesis_validator_deposits: List[Deposit],

# Process genesis deposits
for deposit in genesis_validator_deposits:
process_deposit(
state=state,
pubkey=deposit.deposit_data.deposit_input.pubkey,
amount=deposit.deposit_data.amount,
proof_of_possession=deposit.deposit_data.deposit_input.proof_of_possession,
withdrawal_credentials=deposit.deposit_data.deposit_input.withdrawal_credentials,
)
process_deposit(state, deposit)

# Process genesis activations
for validator_index, _ in enumerate(state.validator_registry):
Expand Down Expand Up @@ -1653,16 +1622,15 @@ Below are the processing steps that happen at every `block`.

* Verify that `block.slot == state.slot`.

#### Proposer signature
#### Block signature

* Let `block_without_signature_root` be the `hash_tree_root` of `block` where `block.signature` is set to `EMPTY_SIGNATURE`.
* Let `proposal_root = hash_tree_root(ProposalSignedData(state.slot, BEACON_CHAIN_SHARD_NUMBER, block_without_signature_root))`.
* Verify that `bls_verify(pubkey=state.validator_registry[get_beacon_proposer_index(state, state.slot)].pubkey, message_hash=proposal_root, signature=block.signature, domain=get_domain(state.fork, get_current_epoch(state), DOMAIN_PROPOSAL))`.
* Let `proposer = state.validator_registry[get_beacon_proposer_index(state, state.slot)]`.
* Let `proposal = Proposal(block.slot, BEACON_CHAIN_SHARD_NUMBER, signed_root(block, "signature"), block.signature)`.
* Verify that `bls_verify(pubkey=proposer.pubkey, message_hash=signed_root(proposal, "signature"), signature=proposal.signature, domain=get_domain(state.fork, get_current_epoch(state), DOMAIN_PROPOSAL))`.

#### RANDAO

* Let `proposer = state.validator_registry[get_beacon_proposer_index(state, state.slot)]`.
* Verify that `bls_verify(pubkey=proposer.pubkey, message_hash=int_to_bytes32(get_current_epoch(state)), signature=block.randao_reveal, domain=get_domain(state.fork, get_current_epoch(state), DOMAIN_RANDAO))`.
* Verify that `bls_verify(pubkey=proposer.pubkey, message_hash=hash_tree_root(get_current_epoch(state)), signature=block.randao_reveal, domain=get_domain(state.fork, get_current_epoch(state), DOMAIN_RANDAO))`.
* Set `state.latest_randao_mixes[get_current_epoch(state) % LATEST_RANDAO_MIXES_LENGTH] = xor(get_randao_mix(state, get_current_epoch(state)), hash(block.randao_reveal))`.

#### Eth1 data
Expand All @@ -1679,12 +1647,12 @@ Verify that `len(block.body.proposer_slashings) <= MAX_PROPOSER_SLASHINGS`.
For each `proposer_slashing` in `block.body.proposer_slashings`:

* Let `proposer = state.validator_registry[proposer_slashing.proposer_index]`.
* Verify that `proposer_slashing.proposal_data_1.slot == proposer_slashing.proposal_data_2.slot`.
* Verify that `proposer_slashing.proposal_data_1.shard == proposer_slashing.proposal_data_2.shard`.
* Verify that `proposer_slashing.proposal_data_1.block_root != proposer_slashing.proposal_data_2.block_root`.
* Verify that `proposer_slashing.proposal_1.slot == proposer_slashing.proposal_2.slot`.
* Verify that `proposer_slashing.proposal_1.shard == proposer_slashing.proposal_2.shard`.
* Verify that `proposer_slashing.proposal_1.block_root != proposer_slashing.proposal_2.block_root`.
* Verify that `proposer.slashed_epoch > get_current_epoch(state)`.
* Verify that `bls_verify(pubkey=proposer.pubkey, message_hash=hash_tree_root(proposer_slashing.proposal_data_1), signature=proposer_slashing.proposal_signature_1, domain=get_domain(state.fork, slot_to_epoch(proposer_slashing.proposal_data_1.slot), DOMAIN_PROPOSAL))`.
* Verify that `bls_verify(pubkey=proposer.pubkey, message_hash=hash_tree_root(proposer_slashing.proposal_data_2), signature=proposer_slashing.proposal_signature_2, domain=get_domain(state.fork, slot_to_epoch(proposer_slashing.proposal_data_2.slot), DOMAIN_PROPOSAL))`.
* Verify that `bls_verify(pubkey=proposer.pubkey, message_hash=signed_root(proposer_slashing.proposal_1, "signature"), signature=proposer_slashing.proposal_1.signature, domain=get_domain(state.fork, slot_to_epoch(proposer_slashing.proposal_1.slot), DOMAIN_PROPOSAL))`.
* Verify that `bls_verify(pubkey=proposer.pubkey, message_hash=signed_root(proposer_slashing.proposal_2, "signature"), signature=proposer_slashing.proposal_2.signature, domain=get_domain(state.fork, slot_to_epoch(proposer_slashing.proposal_2.slot), DOMAIN_PROPOSAL))`.
* Run `slash_validator(state, proposer_slashing.proposer_index)`.

##### Attester slashings
Expand Down Expand Up @@ -1778,13 +1746,7 @@ def verify_merkle_branch(leaf: Bytes32, branch: List[Bytes32], depth: int, index
* Run the following:

```python
process_deposit(
state=state,
pubkey=deposit.deposit_data.deposit_input.pubkey,
amount=deposit.deposit_data.amount,
proof_of_possession=deposit.deposit_data.deposit_input.proof_of_possession,
withdrawal_credentials=deposit.deposit_data.deposit_input.withdrawal_credentials,
)
process_deposit(state, deposit)
```

* Set `state.deposit_index += 1`.
Expand All @@ -1798,8 +1760,7 @@ For each `exit` in `block.body.voluntary_exits`:
* Let `validator = state.validator_registry[exit.validator_index]`.
* Verify that `validator.exit_epoch > get_entry_exit_effect_epoch(get_current_epoch(state))`.
* Verify that `get_current_epoch(state) >= exit.epoch`.
* Let `exit_message = hash_tree_root(VoluntaryExit(epoch=exit.epoch, validator_index=exit.validator_index, signature=EMPTY_SIGNATURE))`.
* Verify that `bls_verify(pubkey=validator.pubkey, message_hash=exit_message, signature=exit.signature, domain=get_domain(state.fork, exit.epoch, DOMAIN_EXIT))`.
* Verify that `bls_verify(pubkey=validator.pubkey, message_hash=signed_root(exit, "signature"), signature=exit.signature, domain=get_domain(state.fork, exit.epoch, DOMAIN_EXIT))`.
* Run `initiate_validator_exit(state, exit.validator_index)`.

##### Transfers
Expand All @@ -1816,8 +1777,7 @@ For each `transfer` in `block.body.transfers`:
* Verify that `state.slot == transfer.slot`.
* Verify that `get_current_epoch(state) >= state.validator_registry[transfer.from].withdrawable_epoch`.
* Verify that `state.validator_registry[transfer.from].withdrawal_credentials == BLS_WITHDRAWAL_PREFIX_BYTE + hash(transfer.pubkey)[1:]`.
* Let `transfer_message = hash_tree_root(Transfer(from=transfer.from, to=transfer.to, amount=transfer.amount, fee=transfer.fee, slot=transfer.slot, signature=EMPTY_SIGNATURE))`.
* Verify that `bls_verify(pubkey=transfer.pubkey, message_hash=transfer_message, signature=transfer.signature, domain=get_domain(state.fork, slot_to_epoch(transfer.slot), DOMAIN_TRANSFER))`.
* Verify that `bls_verify(pubkey=transfer.pubkey, message_hash=signed_root(transfer, "signature"), signature=transfer.signature, domain=get_domain(state.fork, slot_to_epoch(transfer.slot), DOMAIN_TRANSFER))`.
* Set `state.validator_balances[transfer.from] -= transfer.amount + transfer.fee`.
* Set `state.validator_balances[transfer.to] += transfer.amount`.
* Set `state.validator_balances[get_beacon_proposer_index(state, state.slot)] += transfer.fee`.
Expand Down

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