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eth2.0-specs/specs/electra/beacon-chain.md

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# Electra -- The Beacon Chain
**Notice**: This document is a work-in-progress for researchers and implementers.
## Table of contents
<!-- TOC -->
<!-- START doctoc generated TOC please keep comment here to allow auto update -->
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- [Introduction](#introduction)
- [Constants](#constants)
- [Misc](#misc)
- [Preset](#preset)
- [Execution](#execution)
- [Containers](#containers)
- [New containers](#new-containers)
- [`DepositReceipt`](#depositreceipt)
- [`ExecutionLayerExit`](#executionlayerexit)
- [Extended Containers](#extended-containers)
- [`Attestation`](#attestation)
- [`IndexedAttestation`](#indexedattestation)
- [`BeaconBlockBody`](#beaconblockbody)
- [`ExecutionPayload`](#executionpayload)
- [`ExecutionPayloadHeader`](#executionpayloadheader)
- [`BeaconState`](#beaconstate)
- [Helper functions](#helper-functions)
- [Misc](#misc-1)
- [`get_committee_indices`](#get_committee_indices)
- [Beacon state accessors](#beacon-state-accessors)
- [Modified `get_attesting_indices`](#modified-get_attesting_indices)
- [Beacon chain state transition function](#beacon-chain-state-transition-function)
- [Block processing](#block-processing)
- [Modified `process_operations`](#modified-process_operations)
- [Modified `process_attestation`](#modified-process_attestation)
- [New `process_deposit_receipt`](#new-process_deposit_receipt)
- [New `process_execution_layer_exit`](#new-process_execution_layer_exit)
- [Modified `process_execution_payload`](#modified-process_execution_payload)
- [Testing](#testing)
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## Introduction
Electra is a consensus-layer upgrade containing a number of features. Including:
* [EIP-6110](https://eips.ethereum.org/EIPS/eip-6110): Supply validator deposits on chain
* [EIP-7002](https://eips.ethereum.org/EIPS/eip-7002): Execution layer triggerable exits
* [EIP-7549](https://eips.ethereum.org/EIPS/eip-7549): Move committee index outside Attestation
*Note:* This specification is built upon [Deneb](../../deneb/beacon_chain.md) and is under active development.
## Constants
The following values are (non-configurable) constants used throughout the specification.
### Misc
| Name | Value | Description |
| - | - | - |
| `UNSET_DEPOSIT_RECEIPTS_START_INDEX` | `uint64(2**64 - 1)` | *[New in Electra:EIP6110]* |
## Preset
### Execution
| Name | Value | Description |
| - | - | - |
| `MAX_DEPOSIT_RECEIPTS_PER_PAYLOAD` | `uint64(2**13)` (= 8,192) | *[New in Electra:EIP6110]* Maximum number of deposit receipts allowed in each payload |
| `MAX_EXECUTION_LAYER_EXITS` | `2**4` (= 16) | *[New in Electra:EIP7002]* |
| `MAX_ATTESTER_SLASHINGS_ELECTRA` | `2**0` (= 1) | *[New in Electra:EIP7549]* |
| `MAX_ATTESTATIONS_ELECTRA` | `2**3` (= 8) | *[New in Electra:EIP7549]* |
## Containers
### New containers
#### `DepositReceipt`
*Note*: The container is new in EIP6110.
```python
class DepositReceipt(Container):
pubkey: BLSPubkey
withdrawal_credentials: Bytes32
amount: Gwei
signature: BLSSignature
index: uint64
```
#### `ExecutionLayerExit`
*Note*: The container is new in EIP7002.
```python
class ExecutionLayerExit(Container):
source_address: ExecutionAddress
validator_pubkey: BLSPubkey
```
### Modified Containers
#### `AttesterSlashing`
```python
class AttesterSlashing(Container):
attestation_1: IndexedAttestation # [Modified in Electra:EIP7549]
attestation_2: IndexedAttestation # [Modified in Electra:EIP7549]
```
### Extended Containers
#### `Attestation`
```python
class Attestation(Container):
aggregation_bits: Bitlist[MAX_VALIDATORS_PER_COMMITTEE * MAX_COMMITTEES_PER_SLOT] # [Modified in Electra:EIP7549]
data: AttestationData
committee_bits: Bitvector[MAX_COMMITTEES_PER_SLOT] # [New in Electra:EIP7549]
signature: BLSSignature
```
#### `IndexedAttestation`
```python
class IndexedAttestation(Container):
# [Modified in Electra:EIP7549]
attesting_indices: List[ValidatorIndex, MAX_VALIDATORS_PER_COMMITTEE * MAX_COMMITTEES_PER_SLOT]
data: AttestationData
signature: BLSSignature
```
#### `BeaconBlockBody`
```python
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_ELECTRA] # [Modified in Electra:EIP7549]
attestations: List[Attestation, MAX_ATTESTATIONS_ELECTRA] # [Modified in Electra:EIP7549]
deposits: List[Deposit, MAX_DEPOSITS]
voluntary_exits: List[SignedVoluntaryExit, MAX_VOLUNTARY_EXITS]
sync_aggregate: SyncAggregate
# Execution
execution_payload: ExecutionPayload # [Modified in Electra:EIP6110:EIP7002]
bls_to_execution_changes: List[SignedBLSToExecutionChange, MAX_BLS_TO_EXECUTION_CHANGES]
blob_kzg_commitments: List[KZGCommitment, MAX_BLOB_COMMITMENTS_PER_BLOCK]
```
#### `ExecutionPayload`
```python
class ExecutionPayload(Container):
# Execution block header fields
parent_hash: Hash32
fee_recipient: ExecutionAddress
state_root: Bytes32
receipts_root: Bytes32
logs_bloom: ByteVector[BYTES_PER_LOGS_BLOOM]
prev_randao: Bytes32
block_number: uint64
gas_limit: uint64
gas_used: uint64
timestamp: uint64
extra_data: ByteList[MAX_EXTRA_DATA_BYTES]
base_fee_per_gas: uint256
# Extra payload fields
block_hash: Hash32
transactions: List[Transaction, MAX_TRANSACTIONS_PER_PAYLOAD]
withdrawals: List[Withdrawal, MAX_WITHDRAWALS_PER_PAYLOAD]
blob_gas_used: uint64
excess_blob_gas: uint64
deposit_receipts: List[DepositReceipt, MAX_DEPOSIT_RECEIPTS_PER_PAYLOAD] # [New in Electra:EIP6110]
exits: List[ExecutionLayerExit, MAX_EXECUTION_LAYER_EXITS] # [New in Electra:EIP7002]
```
#### `ExecutionPayloadHeader`
```python
class ExecutionPayloadHeader(Container):
# Execution block header fields
parent_hash: Hash32
fee_recipient: ExecutionAddress
state_root: Bytes32
receipts_root: Bytes32
logs_bloom: ByteVector[BYTES_PER_LOGS_BLOOM]
prev_randao: Bytes32
block_number: uint64
gas_limit: uint64
gas_used: uint64
timestamp: uint64
extra_data: ByteList[MAX_EXTRA_DATA_BYTES]
base_fee_per_gas: uint256
# Extra payload fields
block_hash: Hash32
transactions_root: Root
withdrawals_root: Root
blob_gas_used: uint64
excess_blob_gas: uint64
deposit_receipts_root: Root # [New in Electra:EIP6110]
exits_root: Root # [New in Electra:EIP7002]
```
#### `BeaconState`
```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
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
# Participation
previous_epoch_participation: List[ParticipationFlags, VALIDATOR_REGISTRY_LIMIT]
current_epoch_participation: List[ParticipationFlags, VALIDATOR_REGISTRY_LIMIT]
# Finality
justification_bits: Bitvector[JUSTIFICATION_BITS_LENGTH] # Bit set for every recent justified epoch
previous_justified_checkpoint: Checkpoint
current_justified_checkpoint: Checkpoint
finalized_checkpoint: Checkpoint
# Inactivity
inactivity_scores: List[uint64, VALIDATOR_REGISTRY_LIMIT]
# Sync
current_sync_committee: SyncCommittee
next_sync_committee: SyncCommittee
# Execution
latest_execution_payload_header: ExecutionPayloadHeader # [Modified in Electra:EIP6110:EIP7002]
# Withdrawals
next_withdrawal_index: WithdrawalIndex
next_withdrawal_validator_index: ValidatorIndex
# Deep history valid from Capella onwards
historical_summaries: List[HistoricalSummary, HISTORICAL_ROOTS_LIMIT]
# [New in Electra:EIP6110]
deposit_receipts_start_index: uint64
```
## Helper functions
### Misc
#### `get_committee_indices`
```python
def get_committee_indices(commitee_bits: Bitvector) -> Sequence[CommitteeIndex]:
return [CommitteeIndex(index) for index, bit in enumerate(commitee_bits) if bit]
```
### Beacon state accessors
#### Modified `get_attesting_indices`
```python
def get_attesting_indices(state: BeaconState, attestation: Attestation) -> Set[ValidatorIndex]:
"""
Return the set of attesting indices corresponding to ``aggregation_bits`` and ``committee_bits``.
"""
output: Set[ValidatorIndex] = set()
committee_indices = get_committee_indices(attestation.committee_bits)
committee_offset = 0
for index in committee_indices:
committee = get_beacon_committee(state, attestation.data.slot, index)
committee_attesters = set(
index for i, index in enumerate(committee) if attestation.aggregation_bits[committee_offset + i])
output = output.union(committee_attesters)
committee_offset += len(committee)
return output
```
## Beacon chain state transition function
### Block processing
```python
def process_block(state: BeaconState, block: BeaconBlock) -> None:
process_block_header(state, block)
process_withdrawals(state, block.body.execution_payload)
process_execution_payload(state, block.body, EXECUTION_ENGINE) # [Modified in Electra:EIP6110]
process_randao(state, block.body)
process_eth1_data(state, block.body)
process_operations(state, block.body) # [Modified in Electra:EIP6110:EIP7002:EIP7549]
process_sync_aggregate(state, block.body.sync_aggregate)
```
#### Modified `process_operations`
*Note*: The function `process_operations` is modified to process `DepositReceipt` and `ExecutionLayerExit` operations included in the payload, along with the new attestation format.
```python
def process_operations(state: BeaconState, body: BeaconBlockBody) -> None:
# [Modified in Electra:EIP6110]
# Disable former deposit mechanism once all prior deposits are processed
eth1_deposit_index_limit = min(state.eth1_data.deposit_count, state.deposit_receipts_start_index)
if state.eth1_deposit_index < eth1_deposit_index_limit:
assert len(body.deposits) == min(MAX_DEPOSITS, eth1_deposit_index_limit - state.eth1_deposit_index)
else:
assert len(body.deposits) == 0
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) # [Modified in Electra:EIP7549]
for_ops(body.deposits, process_deposit)
for_ops(body.voluntary_exits, process_voluntary_exit)
for_ops(body.execution_payload.exits, process_execution_layer_exit) # [New in Electra:EIP7002]
for_ops(body.bls_to_execution_changes, process_bls_to_execution_change)
# [New in EIP6110]
for_ops(body.execution_payload.deposit_receipts, process_deposit_receipt)
```
#### Modified `process_attestation`
```python
def process_attestation(state: BeaconState, attestation: Attestation) -> None:
data = attestation.data
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
# [Modified in Electra:EIP7549]
assert data.index == 0
committee_indices = get_committee_indices(attestation.committee_bits)
participants_count = 0
for index in committee_indices:
assert index < get_committee_count_per_slot(state, data.target.epoch)
committee = get_beacon_committee(state, data.slot, index)
participants_count += len(committee)
assert len(attestation.aggregation_bits) == participants_count
# Participation flag indices
participation_flag_indices = get_attestation_participation_flag_indices(state, data, state.slot - data.slot)
# Verify signature
assert is_valid_indexed_attestation(state, get_indexed_attestation(state, attestation))
# Update epoch participation flags
if data.target.epoch == get_current_epoch(state):
epoch_participation = state.current_epoch_participation
else:
epoch_participation = state.previous_epoch_participation
proposer_reward_numerator = 0
for index in get_attesting_indices(state, attestation):
for flag_index, weight in enumerate(PARTICIPATION_FLAG_WEIGHTS):
if flag_index in participation_flag_indices and not has_flag(epoch_participation[index], flag_index):
epoch_participation[index] = add_flag(epoch_participation[index], flag_index)
proposer_reward_numerator += get_base_reward(state, index) * weight
# Reward proposer
proposer_reward_denominator = (WEIGHT_DENOMINATOR - PROPOSER_WEIGHT) * WEIGHT_DENOMINATOR // PROPOSER_WEIGHT
proposer_reward = Gwei(proposer_reward_numerator // proposer_reward_denominator)
increase_balance(state, get_beacon_proposer_index(state), proposer_reward)
```
#### New `process_deposit_receipt`
*Note*: This function is new in Electra:EIP6110.
```python
def process_deposit_receipt(state: BeaconState, deposit_receipt: DepositReceipt) -> None:
# Set deposit receipt start index
if state.deposit_receipts_start_index == UNSET_DEPOSIT_RECEIPTS_START_INDEX:
state.deposit_receipts_start_index = deposit_receipt.index
apply_deposit(
state=state,
pubkey=deposit_receipt.pubkey,
withdrawal_credentials=deposit_receipt.withdrawal_credentials,
amount=deposit_receipt.amount,
signature=deposit_receipt.signature,
)
```
#### New `process_execution_layer_exit`
*Note*: This function is new in Electra:EIP7002.
```python
def process_execution_layer_exit(state: BeaconState, execution_layer_exit: ExecutionLayerExit) -> None:
validator_pubkeys = [v.pubkey for v in state.validators]
# Verify pubkey exists
pubkey_to_exit = execution_layer_exit.validator_pubkey
if pubkey_to_exit not in validator_pubkeys:
return
validator_index = ValidatorIndex(validator_pubkeys.index(pubkey_to_exit))
validator = state.validators[validator_index]
# Verify withdrawal credentials
is_execution_address = validator.withdrawal_credentials[:1] == ETH1_ADDRESS_WITHDRAWAL_PREFIX
is_correct_source_address = validator.withdrawal_credentials[12:] == execution_layer_exit.source_address
if not (is_execution_address and is_correct_source_address):
return
# Verify the validator is active
if not is_active_validator(validator, get_current_epoch(state)):
return
# Verify exit has not been initiated
if validator.exit_epoch != FAR_FUTURE_EPOCH:
return
# Verify the validator has been active long enough
if get_current_epoch(state) < validator.activation_epoch + SHARD_COMMITTEE_PERIOD:
return
# Initiate exit
initiate_validator_exit(state, validator_index)
```
#### Modified `process_execution_payload`
*Note*: The function `process_execution_payload` is modified to use the new `ExecutionPayloadHeader` type.
```python
def process_execution_payload(state: BeaconState, body: BeaconBlockBody, execution_engine: ExecutionEngine) -> None:
payload = body.execution_payload
# Verify consistency of the parent hash with respect to the previous execution payload header
assert payload.parent_hash == state.latest_execution_payload_header.block_hash
# Verify prev_randao
assert payload.prev_randao == get_randao_mix(state, get_current_epoch(state))
# Verify timestamp
assert payload.timestamp == compute_timestamp_at_slot(state, state.slot)
# Verify commitments are under limit
assert len(body.blob_kzg_commitments) <= MAX_BLOBS_PER_BLOCK
# Verify the execution payload is valid
versioned_hashes = [kzg_commitment_to_versioned_hash(commitment) for commitment in body.blob_kzg_commitments]
assert execution_engine.verify_and_notify_new_payload(
NewPayloadRequest(
execution_payload=payload,
versioned_hashes=versioned_hashes,
parent_beacon_block_root=state.latest_block_header.parent_root,
)
)
# Cache execution payload header
state.latest_execution_payload_header = ExecutionPayloadHeader(
parent_hash=payload.parent_hash,
fee_recipient=payload.fee_recipient,
state_root=payload.state_root,
receipts_root=payload.receipts_root,
logs_bloom=payload.logs_bloom,
prev_randao=payload.prev_randao,
block_number=payload.block_number,
gas_limit=payload.gas_limit,
gas_used=payload.gas_used,
timestamp=payload.timestamp,
extra_data=payload.extra_data,
base_fee_per_gas=payload.base_fee_per_gas,
block_hash=payload.block_hash,
transactions_root=hash_tree_root(payload.transactions),
withdrawals_root=hash_tree_root(payload.withdrawals),
blob_gas_used=payload.blob_gas_used,
excess_blob_gas=payload.excess_blob_gas,
deposit_receipts_root=hash_tree_root(payload.deposit_receipts), # [New in Electra:EIP6110]
exits_root=hash_tree_root(payload.exits), # [New in Electra:EIP7002]
)
```
## Testing
*Note*: The function `initialize_beacon_state_from_eth1` is modified for pure Electra testing only.
Modifications include:
1. Use `ELECTRA_FORK_VERSION` as the previous and current fork version.
2. Utilize the Electra `BeaconBlockBody` when constructing the initial `latest_block_header`.
3. *[New in Electra:EIP6110]* Add `deposit_receipts_start_index` variable to the genesis state initialization.
```python
def initialize_beacon_state_from_eth1(eth1_block_hash: Hash32,
eth1_timestamp: uint64,
deposits: Sequence[Deposit],
execution_payload_header: ExecutionPayloadHeader=ExecutionPayloadHeader()
) -> BeaconState:
fork = Fork(
previous_version=ELECTRA_FORK_VERSION, # [Modified in Electra:EIP6110] for testing only
current_version=ELECTRA_FORK_VERSION, # [Modified in Electra:EIP6110]
epoch=GENESIS_EPOCH,
)
state = BeaconState(
genesis_time=eth1_timestamp + GENESIS_DELAY,
fork=fork,
eth1_data=Eth1Data(block_hash=eth1_block_hash, deposit_count=uint64(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
deposit_receipts_start_index=UNSET_DEPOSIT_RECEIPTS_START_INDEX, # [New in Electra:EIP6110]
)
# 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
# Set genesis validators root for domain separation and chain versioning
state.genesis_validators_root = hash_tree_root(state.validators)
# Fill in sync committees
# Note: A duplicate committee is assigned for the current and next committee at genesis
state.current_sync_committee = get_next_sync_committee(state)
state.next_sync_committee = get_next_sync_committee(state)
# Initialize the execution payload header
state.latest_execution_payload_header = execution_payload_header
return state
```
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