eth2.0-specs/specs/_features/eip6800/beacon-chain.md

eip6800 -- The Beacon Chain

Table of contents

• Introduction
• Custom types
• Preset
  • Execution
• Containers
  • Extended containers
    • ExecutionPayload
    • ExecutionPayloadHeader
  • New containers
    • SuffixStateDiff
    • StemStateDiff
    • IPAProof
    • VerkleProof
    • ExecutionWitness
• Beacon chain state transition function
  • Execution engine
    • notify_new_payload
  • Block processing
    • Execution payload
      • process_execution_payload
• Testing

Introduction

This upgrade adds transaction execution to the beacon chain as part of the eip6800 upgrade.

Custom types

Name	SSZ equivalent	Description
StateDiff	List[StemStateDiff, MAX_STEMS]	Only valid if list is sorted by stems
BanderwagonGroupElement	Bytes32
BanderwagonFieldElement	Bytes32
Stem	Bytes31

Preset

Execution

Name	Value
MAX_STEMS	2**16
MAX_COMMITMENTS_PER_STEM	33
VERKLE_WIDTH	256
IPA_PROOF_DEPTH	8

Containers

Extended containers

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
    # Extra payload fields
    block_hash: Hash32  # Hash of execution block
    transactions: List[Transaction, MAX_TRANSACTIONS_PER_PAYLOAD]
    withdrawals: List[Withdrawal, MAX_WITHDRAWALS_PER_PAYLOAD]
    execution_witness: ExecutionWitness  # [New in eip6800]

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
    # Extra payload fields
    block_hash: Hash32  # Hash of execution block
    transactions_root: Root
    withdrawals_root: Root
    excess_data_gas: uint256
    execution_witness_root: Root # [New in eip6800]

New containers

SuffixStateDiff

class SuffixStateDiff(Container):
    suffix: Byte
    # Null means not currently present
    current_value: Optional[Bytes32]
    # Null means value not updated
    new_value: Optional[Bytes32]

Note: on the Kaustinen testnet, new_value is omitted from the container.

StemStateDiff

class StemStateDiff(Container):
    stem: Stem
    # Valid only if list is sorted by suffixes
    suffix_diffs: List[SuffixStateDiff, VERKLE_WIDTH]

# Valid only if list is sorted by stems
StateDiff = List[StemStateDiff, MAX_STEMS]

IPAProof

class IpaProof(Container):
    cl: Vector[BanderwagonGroupElement, IPA_PROOF_DEPTH]
    cr: Vector[BanderwagonGroupElement, IPA_PROOF_DEPTH]
    final_evaluation = BanderwagonFieldElement

VerkleProof

class VerkleProof(Container):
    other_stems: List[Bytes31, MAX_STEMS]
    depth_extension_present: ByteList[MAX_STEMS]
    commitments_by_path: List[BanderwagonGroupElement, MAX_STEMS * MAX_COMMITMENTS_PER_STEM]
    d: BanderwagonGroupElement
    ipa_proof: IpaProof

ExecutionWitness

class ExecutionWitness(container):
    state_diff: StateDiff
    verkle_proof: VerkleProof

Beacon chain state transition function

Block processing

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,
        block_hash=payload.block_hash,
        transactions_root=hash_tree_root(payload.transactions),
        withdrawals_root=hash_tree_root(payload.withdrawals),
        excess_data_gas=payload.excess_data_gas,
        execution_witness=payload.execution_witness, # [New in eip6800]
    )

Testing

TBD