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# Executable beacon chain spec
# Beacon chain
## Configuration
### Execution
|Name|Value|
|-|-|
|MAX_BYTES_PER_TRANSACTION_PAYLOAD|2**20|
|MAX_APPLICATION_TRANSACTIONS|2**14|
|BYTES_PER_LOGS_BLOOM|2**8 (= 256)|
|BLOCK_ROOTS_FOR_EVM_SIZE|2**8 (= 256)|
## Updated containers
### Updated `BeaconState`
*Note*: `BeaconState` fields remain unchanged other than the removal of `eth1_data_votes` and addition of `application_state_root`. The latter stores the root hash of ethereum application state.
```python=
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
# [removed] eth1_data_votes
eth1_deposit_index: uint64
application_state_root: Bytes32
# 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
```
### Extended `BeaconBlockBody`
*Note*: `BeaconBlockBody` fields remain unchanged other than the addition of `application_payload`.
```python=
class BeaconBlockBody(phase0.BeaconBlockBody):
application_payload: ApplicationPayload # User execution payload
```
## New containers
### `Transaction`
Application transaction fields structured as an SSZ object for inclusion in an `ApplicationPayload` contained within a `BeaconBlock`.
```python=
class Transaction(Container):
nonce: uint64
gas_price: uint256
gas_limit: uint64
recipient: Bytes20
value: uint256
input: List[Bytes1, MAX_BYTES_PER_TRANSACTION_PAYLOAD]
v: uint256
r: uint256
s: uint256
```
### `ApplicationPayload`
The application payload included in a `BeaconBlock`.
```python=
class ApplicationPayload(Container):
parent_hash: Bytes32 # Hash of parent of virtial eth1 block
block_hash: Bytes32 # Hash of virtual eth1 block
coinbase: Bytes20
state_root: Bytes32
gas_limit: uint64
gas_used: uint64
receipt_root: Bytes32
logs_bloom: Vector[Bytes1, BYTES_PER_LOGS_BLOOM]
difficulty: uint64 # Temporary field, will be removed later on
transactions: List[Transaction, MAX_APPLICATION_TRANSACTIONS]
```
## Helper functions
```python=
def compute_time_at_slot(state: BeaconState, slot: Slot) -> uint64:
return uint64(state.genesis_time + slot * SECONDS_PER_SLOT)
```
```python=
def get_recent_beacon_block_roots(state: BeaconState, qty: uint64) -> Sequence[Bytes32]:
return [get_block_root_at_slot(state.slot - i) if GENESIS_SLOT + i < state.slot else Bytes32() for i in reversed(range(1, qty + 1))]
```
```python=
def get_beacon_block_roots_for_evm(state: BeaconState) -> Sequence[Bytes32]:
num_block_roots = min(BLOCK_ROOTS_FOR_EVM_SIZE, SLOTS_PER_HISTORICAL_ROOT)
return get_recent_beacon_block_roots(state, num_block_roots)
```
```python=
def compute_randao_mix(state: BeaconState, randao_reveal: BLSSignature) -> Bytes32:
epoch = get_current_epoch(state)
return xor(get_randao_mix(state, epoch), hash(randao_reveal))
```
```python=
def get_application_block_hash(block: BeaconBlock) -> Bytes32:
return block.body.application_payload.block_hash
```
## Block processing
```python=
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)
process_application_payload(state, block.body)
```
### Eth1 data
```python=
def process_eth1_data(state: BeaconState, body: BeaconBlockBody) -> None:
state.eth1_data = body.eth1_data
```
### Application payload
#### `ApplicationState`
Let `class ApplicationState` be the abstract class representing ethereum application state.
#### `BeaconChainData`
```python=
class BeaconChainData(Container):
slot: Slot
randao_mix: Bytes32
timestamp: uint64
recent_block_roots: Sequence[Bytes32]
```
#### `get_application_state`
Let `get_application_state(application_state_root: Bytes32) -> ApplicationState` be the function that given the root hash returns a copy of ethereum application state. The body of the function is implementation dependant.
#### Application state transition function
Let `application_state_transition(application_state: ApplicationState, beacon_chain_data: BeaconChainData, application_payload: ApplicationPayload) -> None` be the transition function of ethereum application state. The body of the function is implementation dependant.
_Note:_ `application_state_transition` must throw `AssertionError` if either transition or post-transition verifications has failed.
_Note:_ one of potential implementations of this function is delegating the call to [eth2_insertBlock](https://hackmd.io/T9x2mMA4S7us8tJwEB3FDQ?view#eth2_insertBlock).
#### `process_application_payload`
```python=
def process_application_payload(state: BeaconState, body: BeaconBlockBody) -> None:
"""
Note: This function is designed to be able to be run in parallel with
the other `process_block` sub-functions
"""
# Utilizes `compute_randao_mix` to avoid any assumptions about
# the processing of other `process_block` sub-functions
beacon_chain_data = BeaconChainData(
slot=state.slot,
randao_mix=compute_randao_mix(state, body.randao_reveal),
timestamp=compute_time_at_slot(state.genesis_time, state.slot),
recent_block_roots=get_beacon_block_roots_for_evm(state)
)
application_state = get_application_state(state.application_state_root)
application_state_transition(application_state, beacon_chain_data, body.application_payload)
state.application_state_root = body.application_payload.state_root
```
# Fork choice
_Notes:_
* **Eth1 data**: Eth1 data included in a block must correspond to the Eth1 state produced by the execution part of the parent block. This acts as an additional filter on the block subtree under consideration for the beacon block fork choice.
## Helpers
### `get_eth1_data`
Let `get_eth1_data(application_state_root: Bytes32) -> Eth1Data` be the function that returns the [`Eth1Data`](https://github.com/ethereum/eth2.0-specs/blob/dev/specs/phase0/beacon-chain.md#eth1data) obtained from the application state specified by `application_state_root`.
*Note*: This is a function of the state of the beacon chain deposit contract. It can be read from the eth1 state and/or logs.
### `is_valid_eth1_data`
Used by fork-choice handler, `on_block`, to
```python=
def is_valid_eth1_data(store: Store, block: BeaconBlock) -> boolean:
parent_state = store.block_states[block.parent_root]
expected_eth1_data = get_eth1_data(parent_state.application_state_root)
actual_eth1_data = block.body.eth1_data
is_correct_root = expected_eth1_data.deposit_root == actual_eth1_data.deposit_root
is_correct_count = expected_eth1_data.deposit_count == actual_eth1_data.deposit_count
return is_correct_root and is_correct_count
```
## Updated fork-choice handlers
### `on_block`
*Note*: The only modification is the addition of the `Eth1Data` validity assumption.
```python=
def on_block(store: Store, signed_block: SignedBeaconBlock) -> None:
block = signed_block.message
# Parent block must be known
assert block.parent_root in store.block_states
# Make a copy of the state to avoid mutability issues
pre_state = copy(store.block_states[block.parent_root])
# Blocks cannot be in the future. If they are, their consideration must be delayed until the are in the past.
assert get_current_slot(store) >= block.slot
# Check that block is later than the finalized epoch slot (optimization to reduce calls to get_ancestor)
finalized_slot = compute_start_slot_at_epoch(store.finalized_checkpoint.epoch)
assert block.slot > finalized_slot
# Check block is a descendant of the finalized block at the checkpoint finalized slot
assert get_ancestor(store, block.parent_root, finalized_slot) == store.finalized_checkpoint.root
# [Added] Check that Eth1 data is correct
assert is_valid_eth1_data(store, block)
# Check the block is valid and compute the post-state
state = pre_state.copy()
state_transition(state, signed_block, True)
# Add new block to the store
store.blocks[hash_tree_root(block)] = block
# Add new state for this block to the store
store.block_states[hash_tree_root(block)] = state
# Update justified checkpoint
if state.current_justified_checkpoint.epoch > store.justified_checkpoint.epoch:
if state.current_justified_checkpoint.epoch > store.best_justified_checkpoint.epoch:
store.best_justified_checkpoint = state.current_justified_checkpoint
if should_update_justified_checkpoint(store, state.current_justified_checkpoint):
store.justified_checkpoint = state.current_justified_checkpoint
# Update finalized checkpoint
if state.finalized_checkpoint.epoch > store.finalized_checkpoint.epoch:
store.finalized_checkpoint = state.finalized_checkpoint
# Potentially update justified if different from store
if store.justified_checkpoint != state.current_justified_checkpoint:
# Update justified if new justified is later than store justified
if state.current_justified_checkpoint.epoch > store.justified_checkpoint.epoch:
store.justified_checkpoint = state.current_justified_checkpoint
return
# Update justified if store justified is not in chain with finalized checkpoint
finalized_slot = compute_start_slot_at_epoch(store.finalized_checkpoint.epoch)
ancestor_at_finalized_slot = get_ancestor(store, store.justified_checkpoint.root, finalized_slot)
if ancestor_at_finalized_slot != store.finalized_checkpoint.root:
store.justified_checkpoint = state.current_justified_checkpoint
```
# Validator
## Beacon chain responsibilities
All validator responsibilities remain unchanged other than those noted below. Namely, the modification of `Eth1Data` and the addition of `ApplicationPayload`.
### Block proposal
#### Constructing the `BeaconBlockBody`
##### Eth1 Data
The `block.body.eth1_data` field is for block proposers to publish recent Eth1 data. This recent data contains deposit root (as calculated by the `get_deposit_root()` method of the deposit contract) and deposit count after processing of the `parent` block. The fork choice verifies Eth1 data of a block, then `state.eth1_data` updates immediately allowing new deposits to be processed. Each deposit in `block.body.deposits` must verify against `state.eth1_data.eth1_deposit_root`.
###### `get_eth1_data`
Let `get_eth1_data(application_state_root: Bytes32) -> Eth1Data` be the function that returns the [`Eth1Data`](https://github.com/ethereum/eth2.0-specs/blob/dev/specs/phase0/beacon-chain.md#eth1data) obtained from the application state specified by `application_state_root`.
*Note*: This is a function of the state of the beacon chain deposit contract. It can be read from the eth1 state and/or logs.
* Set `block.body.eth1_data = get_eth1_data(state.application_state_root)`.
##### Application Payload
###### `produce_application_payload`
Let `produce_application_payload(parent_hash: Bytes32, beacon_chain_data: BeaconChainData) -> ApplicationPayload` be the function that produces new instance of application payload.
_Note:_ one of potential implementations of this function is delegating the call to [eth2_produceBlock](https://hackmd.io/T9x2mMA4S7us8tJwEB3FDQ?view#eth2_produceBlock).
* Let `randao_reveal` be `block.body.randao_reveal` of the block that is being produced
* Set `block.body.application_payload = get_application_payload(state, parent, randao_reveal)` where:
```python=
def get_application_payload(state: BeaconState,
parent: BeaconBlock,
randao_reveal: BLSSignature) -> ApplicationPayload:
application_parent_hash = get_application_block_hash(parent)
beacon_chain_data = BeaconChainData(
slot=state.slot,
randao_mix=compute_randao_mix(state, randao_reveal),
timestamp=compute_time_at_slot(state.genesis_time, state.slot),
recent_block_roots=get_beacon_block_roots_for_evm(state)
)
return produce_application_payload(application_parent_hash, beacon_chain_data)
```
# Network Upgrade
TBD
