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Deneb -- The Beacon Chain

Notice: This document is a work-in-progress for researchers and implementers.

Introduction
Custom types
Constants
- Blob
Preset
- Execution
Configuration
Containers
- Extended containers
Helper functions
- Misc
Beacon chain state transition function
- Block processing
  - Execution payload
    - process_execution_payload
  - Blob KZG commitments
Testing

Introduction

This upgrade adds blobs to the beacon chain as part of Deneb. This is an extension of the Capella upgrade.

Custom types

Name	SSZ equivalent	Description
`VersionedHash`	`Bytes32`
`BlobIndex`	`uint64`

Constants

Domain types

Name	Value
`DOMAIN_BLOB_SIDECAR`	`DomainType('0x0B000000')`

Blob

Name	Value
`BLOB_TX_TYPE`	`uint8(0x05)`
`VERSIONED_HASH_VERSION_KZG`	`Bytes1('0x01')`

Preset

Execution

Name	Value
`MAX_BLOBS_PER_BLOCK`	`uint64(2**2)` (= 4)

Configuration

Containers

Extended containers

`BeaconBlockBody`

Note: BeaconBlock and SignedBeaconBlock types are updated indirectly.

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]
    attestations: List[Attestation, MAX_ATTESTATIONS]
    deposits: List[Deposit, MAX_DEPOSITS]
    voluntary_exits: List[SignedVoluntaryExit, MAX_VOLUNTARY_EXITS]
    sync_aggregate: SyncAggregate
    # Execution
    execution_payload: ExecutionPayload  # [Modified in Deneb]
    bls_to_execution_changes: List[SignedBLSToExecutionChange, MAX_BLS_TO_EXECUTION_CHANGES]
    blob_kzg_commitments: List[KZGCommitment, MAX_BLOBS_PER_BLOCK]  # [New in Deneb]

`ExecutionPayload`

class ExecutionPayload(Container):
    # Execution block header fields
    parent_hash: Hash32
    fee_recipient: ExecutionAddress  # 'beneficiary' in the yellow paper
    state_root: Bytes32
    receipts_root: Bytes32
    logs_bloom: ByteVector[BYTES_PER_LOGS_BLOOM]
    prev_randao: Bytes32  # 'difficulty' in the yellow paper
    block_number: uint64  # 'number' in the yellow paper
    gas_limit: uint64
    gas_used: uint64
    timestamp: uint64
    extra_data: ByteList[MAX_EXTRA_DATA_BYTES]
    base_fee_per_gas: uint256
    excess_data_gas: uint256  # [New in Deneb]
    # Extra payload fields
    block_hash: Hash32  # Hash of execution block
    transactions: List[Transaction, MAX_TRANSACTIONS_PER_PAYLOAD]
    withdrawals: List[Withdrawal, MAX_WITHDRAWALS_PER_PAYLOAD]

`ExecutionPayloadHeader`

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
    excess_data_gas: uint256  # [New in Deneb]
    # Extra payload fields
    block_hash: Hash32  # Hash of execution block
    transactions_root: Root
    withdrawals_root: Root

Helper functions

Misc

`kzg_commitment_to_versioned_hash`

def kzg_commitment_to_versioned_hash(kzg_commitment: KZGCommitment) -> VersionedHash:
    return VERSIONED_HASH_VERSION_KZG + hash(kzg_commitment)[1:]

`tx_peek_blob_versioned_hashes`

This function retrieves the hashes from the SignedBlobTransaction as defined in Deneb, using SSZ offsets. Offsets are little-endian uint32 values, as defined in the SSZ specification. See the full details of blob_versioned_hashes offset calculation.

def tx_peek_blob_versioned_hashes(opaque_tx: Transaction) -> Sequence[VersionedHash]:
    assert opaque_tx[0] == BLOB_TX_TYPE
    message_offset = 1 + uint32.decode_bytes(opaque_tx[1:5])
    # field offset: 32 + 8 + 32 + 32 + 8 + 4 + 32 + 4 + 4 + 32 = 188
    blob_versioned_hashes_offset = (
        message_offset
        + uint32.decode_bytes(opaque_tx[(message_offset + 188):(message_offset + 192)])
    )
    return [
        VersionedHash(opaque_tx[x:(x + 32)])
        for x in range(blob_versioned_hashes_offset, len(opaque_tx), 32)
    ]

`verify_kzg_commitments_against_transactions`

def verify_kzg_commitments_against_transactions(transactions: Sequence[Transaction],
                                                kzg_commitments: Sequence[KZGCommitment]) -> bool:
    all_versioned_hashes: List[VersionedHash] = []
    for tx in transactions:
        if tx[0] == BLOB_TX_TYPE:
            all_versioned_hashes += tx_peek_blob_versioned_hashes(tx)
    return all_versioned_hashes == [kzg_commitment_to_versioned_hash(commitment) for commitment in kzg_commitments]

Beacon chain state transition function

Block processing

def process_block(state: BeaconState, block: BeaconBlock) -> None:
    process_block_header(state, block)
    if is_execution_enabled(state, block.body):
        process_withdrawals(state, block.body.execution_payload)
        process_execution_payload(state, block.body.execution_payload, EXECUTION_ENGINE)  # [Modified in Deneb]
    process_randao(state, block.body)
    process_eth1_data(state, block.body)
    process_operations(state, block.body)
    process_sync_aggregate(state, block.body.sync_aggregate)
    process_blob_kzg_commitments(state, block.body)  # [New in Deneb]

Execution payload

`process_execution_payload`

def process_execution_payload(state: BeaconState, payload: ExecutionPayload, execution_engine: ExecutionEngine) -> None:
    # Verify consistency of the parent hash with respect to the previous execution payload header
    if is_merge_transition_complete(state):
        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 the execution payload is valid
    assert execution_engine.notify_new_payload(payload)

    # 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,
        excess_data_gas=payload.excess_data_gas,  # [New in Deneb]
        block_hash=payload.block_hash,
        transactions_root=hash_tree_root(payload.transactions),
        withdrawals_root=hash_tree_root(payload.withdrawals),
    )

Blob KZG commitments

def process_blob_kzg_commitments(state: BeaconState, body: BeaconBlockBody) -> None:
    # pylint: disable=unused-argument
    assert verify_kzg_commitments_against_transactions(body.execution_payload.transactions, body.blob_kzg_commitments)

Testing

Note: The function initialize_beacon_state_from_eth1 is modified for pure Deneb testing only.

The BeaconState initialization is unchanged, except for the use of the updated deneb.BeaconBlockBody type when initializing the first body-root.

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=DENEB_FORK_VERSION,  # [Modified in Deneb] for testing only
        current_version=DENEB_FORK_VERSION,  # [Modified in Deneb]
        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
    )

    # 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
    # If empty, will initialize a chain that has not yet gone through the Merge transition
    state.latest_execution_payload_header = execution_payload_header

    return state

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