Abstract

This EIP introduces Block-Level Access Lists (BALs) that record all accounts and storage locations accessed during block execution, along with their post-execution values. BALs enable parallel disk reads, parallel transaction validation, and executionless state updates.

Motivation

Transaction execution cannot be parallelized without knowing in advance which addresses and storage slots will be accessed. While EIP-2930 introduced optional transaction access lists, they are not enforced.

This proposal enforces access lists at the block level, enabling:

• Parallel disk reads and transaction execution
• State reconstruction without executing transactions
• Reduced execution time to parallel IO + parallel EVM

Specification

Block Structure Modification

We introduce a new field to the block header:

class Header:
    # Existing fields
    ...
    
    block_access_list_hash: Hash32

The block body includes a BlockAccessList containing all account accesses and state changes.

RLP Data Structures

BALs use RLP encoding following the pattern: address -> field -> block_access_index -> change.

# Type aliases for RLP encoding
Address = bytes  # 20-byte Ethereum address
StorageKey = bytes  # 32-byte storage slot key  
StorageValue = bytes  # 32-byte storage value
CodeData = bytes  # Variable-length contract bytecode
BlockAccessIndex = uint16  # Block access index (0 for pre-execution, 1..n for transactions, n+1 for post-execution)
Balance = uint256  # Post-transaction balance in wei
Nonce = uint64  # Account nonce

# Constants; chosen to support a 630m block gas limit
MAX_TXS = 30_000
MAX_SLOTS = 300_000
MAX_ACCOUNTS = 300_000
MAX_CODE_SIZE = 24_576  # Maximum contract bytecode size in bytes
MAX_CODE_CHANGES = 1

# Core change structures (RLP encoded as lists)
# StorageChange: [block_access_index, new_value]
StorageChange = [BlockAccessIndex, StorageValue]

# BalanceChange: [block_access_index, post_balance]
BalanceChange = [BlockAccessIndex, Balance]

# NonceChange: [block_access_index, new_nonce]
NonceChange = [BlockAccessIndex, Nonce]

# CodeChange: [block_access_index, new_code]
CodeChange = [BlockAccessIndex, CodeData]

# SlotChanges: [slot, [changes]]
# All changes to a single storage slot
SlotChanges = [StorageKey, List[StorageChange]]

# AccountChanges: [address, storage_changes, storage_reads, balance_changes, nonce_changes, code_changes]
# All changes for a single account, grouped by field type
AccountChanges = [
    Address,                    # address
    List[SlotChanges],          # storage_changes (slot -> [block_access_index -> new_value])
    List[StorageKey],           # storage_reads (read-only storage keys)
    List[BalanceChange],        # balance_changes ([block_access_index -> post_balance])
    List[NonceChange],          # nonce_changes ([block_access_index -> new_nonce])
    List[CodeChange]            # code_changes ([block_access_index -> new_code])
]

# BlockAccessList: List of AccountChanges
BlockAccessList = List[AccountChanges]

Scope and Inclusion

BlockAccessList is the set of all addresses accessed during block execution.

It MUST include:

• Addresses with state changes (storage, balance, nonce, or code).
• Addresses accessed without state changes (e.g., STATICCALL targets, BALANCE opcode targets).

Addresses with no state changes MUST still be present with empty change lists.

Entries from an EIP-2930 access list MUST NOT be included automatically. Only addresses and storage slots that are actually touched or changed during execution are recorded.

Ordering and Determinism

The following ordering rules MUST apply:

• Addresses: lexicographic (bytewise).
• Storage keys: lexicographic within each account.
• Block access indices: ascending within each change list.

BlockAccessIndex Assignment

BlockAccessIndex values MUST be assigned as follows:

• 0 for pre‑execution system contract calls.
• 1 … n for transactions (in block order).
• n + 1 for post‑execution system contract calls.

Recording Semantics by Change Type

Storage

• Writes include:

  • Any value change (post‑value ≠ pre‑value).
  • Zeroing a slot (pre‑value exists, post‑value is zero).

• Reads include:

  • Slots accessed via SLOAD that are not written.
  • Slots written with unchanged values (i.e., SSTORE that re‑stores the same value).

Balance (balance_changes)

Record post‑transaction balances (uint128) for:

• Transaction senders (gas + value).
• Transaction recipients (only if value > 0).
• Coinbase (rewards + fees).
• SELFDESTRUCT/SENDALL beneficiaries.
• Withdrawal recipients (system withdrawals, EIP-4895).

Zero‑value transfers: MUST NOT be recorded in balance_changes, but the corresponding addresses MUST still be included with empty AccountChanges.

Code

Track post‑transaction runtime bytecode for deployed or modified contracts, and delegation indicators as defined in EIP-7702.

Nonce

Record post‑transaction nonces for:

• EOA senders.
• Contracts that performed a successful CREATE or CREATE2.
• Deployed contracts.
• EIP-7702 authorities.

Edge Cases (Normative)

• SELFDESTRUCT/SENDALL: Beneficiary is recorded as a balance change.
• Accessed but unchanged: Include the address with empty changes (e.g., targets of EXTCODEHASH, EXTCODESIZE, BALANCE, STATICCALL, etc.).
• Zero‑value transfers: Include the address; omit from balance_changes.
• Gas refunds: Record the final balance of the sender after each transaction.
• Block rewards: Record the final balance of the fee recipient after each transaction.
• Exceptional halts: Record the final nonce and balance of the sender, and the final balance of the fee recipient after each transaction.
• Pre‑execution system contract calls: All state changes MUST use block_access_index = 0.
• Post‑execution system contract calls: All state changes MUST use block_access_index = len(transactions) + 1.
• EIP‑4895 (Consensus layer withdrawals): Recipients are recorded with their final balance after the withdrawal.
• EIP‑2935 (block hash): Record system contract storage diffs of the single updated storage slot in the ring buffer.
• EIP‑4788 (beacon root): Record system contract storage diffs of the two updated storage slots in the ring buffer.
• EIP‑7002 (withdrawals): Record system contract storage diffs of storage slots 0–3 (4 slots) after the dequeuing call.
• EIP‑7251 (consolidations): Record system contract storage diffs of storage slots 0–3 (4 slots) after the dequeuing call.

Engine API

The execution layer computes:

block_access_list_hash = keccak256(rlp.encode(block_access_list))

and provides both block_access_list and block_access_list_hash in the ExecutionPayload to the consensus layer, which stores them without modification.

State Transition Function

The state transition function must validate that the provided BAL matches the actual state accesses:

def validate_block(block):
    # 1. Verify provided BAL matches header hash
    import rlp
    provided_bal_hash = keccak256(rlp.encode(block.block_access_list))
    assert provided_bal_hash == block.header.block_access_list_hash
    
    # 2. Execute block and collect actual accesses
    actual_bal = execute_and_collect_accesses(block)
    
    # 3. Verify actual execution matches provided BAL
    actual_bal_hash = keccak256(rlp.encode(actual_bal))
    assert actual_bal_hash == block.header.block_access_list_hash

def execute_and_collect_accesses(block):
    """Execute block and collect all state accesses into BAL format"""
    accesses = {}
    
    # Pre-execution system contracts (block_access_index = 0)
    track_system_contracts_pre(block, accesses, block_access_index=0)
    
    # Execute transactions (block_access_index = 1..n)
    for i, tx in enumerate(block.transactions):
        execute_transaction(tx)
        track_state_changes(tx, accesses, block_access_index=i+1)
    
    # Withdrawals and post-execution (block_access_index = len(txs) + 1)
    post_index = len(block.transactions) + 1
    for withdrawal in block.withdrawals:
        apply_withdrawal(withdrawal)
        track_balance_change(withdrawal.address, accesses, post_index)
    track_system_contracts_post(block, accesses, post_index)
    
    # Convert to BAL format and sort
    return build_bal(accesses)

def track_state_changes(tx, accesses, block_access_index):
    """Track all state changes from a transaction"""
    for addr in get_touched_addresses(tx):
        if addr not in accesses:
            accesses[addr] = {
                'storage_writes': {},  # slot -> [(index, value)]
                'storage_reads': set(),
                'balance_changes': [],
                'nonce_changes': [],
                'code_changes': []
            }
        
        # Track storage changes
        for slot, value in get_storage_writes(addr).items():
            if slot not in accesses[addr]['storage_writes']:
                accesses[addr]['storage_writes'][slot] = []
            accesses[addr]['storage_writes'][slot].append((block_access_index, value))
        
        # Track reads (slots accessed but not written)
        for slot in get_storage_reads(addr):
            if slot not in accesses[addr]['storage_writes']:
                accesses[addr]['storage_reads'].add(slot)
        
        # Track balance, nonce, code changes
        if balance_changed(addr):
            accesses[addr]['balance_changes'].append((block_access_index, get_balance(addr)))
        if nonce_changed(addr):
            accesses[addr]['nonce_changes'].append((block_access_index, get_nonce(addr)))
        if code_changed(addr):
            accesses[addr]['code_changes'].append((block_access_index, get_code(addr)))

def build_bal(accesses):
    """Convert collected accesses to BAL format"""
    bal = []
    for addr in sorted(accesses.keys()):  # Sort addresses lexicographically
        data = accesses[addr]
        
        # Format storage changes: [slot, [[index, value], ...]]
        storage_changes = [[slot, sorted(changes)] 
                          for slot, changes in sorted(data['storage_writes'].items())]
        
        # Account entry: [address, storage_changes, reads, balance_changes, nonce_changes, code_changes]
        bal.append([
            addr,
            storage_changes,
            sorted(list(data['storage_reads'])),
            sorted(data['balance_changes']),
            sorted(data['nonce_changes']),
            sorted(data['code_changes'])
        ])
    
    return bal

The BAL MUST be complete and accurate. Missing or spurious entries invalidate the block.

Clients MUST validate by comparing execution-gathered accesses (per EIP-2929) with the BAL.

Clients MAY invalidate immediately if any transaction exceeds declared state.

Concrete Example

Example block:

Pre-execution:

• EIP-2935: Store parent hash at block hash contract (0x0000F90827F1C53a10cb7A02335B175320002935)
• EIP-7002: Omitted for simplicity.

Transactions:

1. Alice (0xaaaa...) sends 1 ETH to Bob (0xbbbb...), checks balance of 0x2222...
2. Charlie (0xcccc...) calls factory (0xffff...) deploying contract at 0xdddd...

Post-execution:

• Withdrawal of 100 ETH to Eve (0xabcd...)
• EIP-7002 and EIP-7251 omitted for simplicity.

Note: Pre-execution system contract uses block_access_index = 0 Post-execution withdrawal uses block_access_index = 3 (len(transactions) + 1)

Resulting BAL (RLP structure):

[
    # Addresses are sorted lexicographically
    [ # AccountChanges for 0x0000F90827F1C53a10cb7A02335B175320002935 (Block hash contract)
        0x0000F90827F1C53a10cb7A02335B175320002935,
        [ # storage_changes
            [b'\x00...\x0f\xa0', [[0, b'...']]]  # slot, [[block_access_index, parent_hash]]
        ],
        [],  # storage_reads
        [],  # balance_changes
        [],  # nonce_changes
        []   # code_changes
    ],
    [ # AccountChanges for 0x2222... (Address checked by Alice)
        0x2222...,
        [],  # storage_changes
        [],  # storage_reads
        [],  # balance_changes (no change, just checked)
        [],  # nonce_changes
        []   # code_changes
    ],
    [ # AccountChanges for 0xaaaa... (Alice - sender tx 0)
        0xaaaa...,
        [],  # storage_changes
        [],  # storage_reads
        [[1, 0x...29a241a]],  # balance_changes: [[block_access_index, post_balance]]
        [[1, 10]],  # nonce_changes: [[block_access_index, new_nonce]]
        []  # code_changes
    ],
    [ # AccountChanges for 0xabcd... (Eve - withdrawal recipient)
        0xabcd...,
        [],  # storage_changes
        [],  # storage_reads
        [[3, 0x...5f5e100]],  # balance_changes: 100 ETH withdrawal
        [],  # nonce_changes
        []   # code_changes
    ],
    [ # AccountChanges for 0xbbbb... (Bob - recipient tx 0)
        0xbbbb...,
        [],  # storage_changes
        [],  # storage_reads
        [[1, 0x...b9aca00]],  # balance_changes: +1 ETH
        [],  # nonce_changes
        []   # code_changes
    ],
    [ # AccountChanges for 0xcccc... (Charlie - sender tx 1)
        0xcccc...,
        [],  # storage_changes
        [],  # storage_reads
        [[2, 0x...bc16d67]],  # balance_changes: after gas
        [[2, 5]],  # nonce_changes
        []  # code_changes
    ],
    [ # AccountChanges for 0xdddd... (Deployed contract)
        0xdddd...,
        [],  # storage_changes
        [],  # storage_reads
        [],  # balance_changes
        [[2, 1]],  # nonce_changes: new contract nonce
        [[2, b'\x60\x80\x60\x40...']]  # code_changes: deployed bytecode
    ],
    [ # AccountChanges for 0xeeee... (Coinbase)
        0xeeee...,
        [],  # storage_changes
        [],  # storage_reads
        [[1, 0x...05f5e1], [2, 0x...0bebc2]],  # balance_changes: after tx fees
        [],  # nonce_changes
        []   # code_changes
    ],
    [ # AccountChanges for 0xffff... (Factory contract)
        0xffff...,
        [ # storage_changes
            [b'\x00...\x01', [[2, b'\x00...\xdd\xdd...']]]  # slot 1, deployed address
        ],
        [],  # storage_reads
        [],  # balance_changes
        [[2, 5]],  # nonce_changes: after CREATE
        []  # code_changes
    ]
]

RLP-encoded and compressed: ~400-500 bytes.

Rationale

BAL Design Choice

This design variant was chosen for several key reasons:

1. Size vs parallelization: BALs include all accessed addresses (even unchanged) for complete parallel IO and execution.

2. Storage values for writes: Post-execution values enable state reconstruction during sync without individual proofs against state root.

3. Overhead analysis: Historical data shows ~45 KiB average BAL size.

4. Transaction independence: 60-80% of transactions access disjoint storage slots, enabling effective parallelization. The remaining 20-40% can be parallelized by having post-transaction state diffs.

5. RLP encoding: Native Ethereum encoding format, maintains compatibility with existing infrastructure.

Block Size Considerations

Block size impact (historical analysis):

• Average: ~40 KiB (compressed)
• Balance diffs: ~4.5 KiB (compressed)
• Storage diffs: ~33.88 KiB (compressed)
• Nonce diffs: ~0.02 KiB (compressed)
• Code diffs: ~0.6 KiB (compressed)
• Worst-case (36m gas): ~0.93 MiB
• Worst-case balance diffs: ~0.12 MiB

Smaller than current worst-case calldata blocks.

An empirical analysis has been done here.

Asynchronous Validation

BAL verification occurs alongside parallel IO and EVM operations without delaying block processing.

Backwards Compatibility

This proposal requires changes to the block structure that are not backwards compatible and require a hard fork.

Security Considerations

Validation Overhead

Validating access lists and balance diffs adds validation overhead but is essential to prevent acceptance of invalid blocks.

Block Size

Increased block size impacts propagation but overhead (~40 KiB average) is reasonable for performance gains.

Copyright

Copyright and related rights waived via CC0.