EIP-7928 - Block-Level Access Lists

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, block_access_list_hash, which contains the Keccak-256 hash of the RLP-encoded block access list. When no state changes are present, this field is the hash of an empty rlp list 0x1dcc4de8dec75d7aab85b567b6ccd41ad312451b948a7413f0a142fd40d49347, i.e. keccak256(rlp.encode([])).

class Header:
    # Existing fields
    ...

    block_access_list_hash: Hash32 = keccak256(rlp.encode(block_access_list))

The block body includes a BlockAccessList containing all account accesses and state changes. This field is RLP-encoded as a list of AccountChanges. When no state changes are present, this field is the empty RLP list 0xc0, i.e. rlp.encode([]).

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

# 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, including:

  • Targets of BALANCE, EXTCODESIZE, EXTCODECOPY, EXTCODEHASH opcodes
  • Targets of CALL, CALLCODE, DELEGATECALL, STATICCALL (even if they revert)
  • Target addresses of CREATE/CREATE2 (even when creation fails)
  • Transaction sender and recipient addresses (even for zero-value transfers)
  • Coinbase address when receiving transaction fees
  • Beneficiary addresses for SELFDESTRUCT
  • System contract addresses accessed during pre/post-execution
  • Withdrawal recipient addresses
  • Precompiled contracts when called or accessed

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:

• Accounts: Lexicographic by address
• storage_changes: Slots lexicographic by storage key; within each slot, changes by block access index index (ascending)
• storage_reads: Lexicographic by storage key
• balance_changes, nonce_changes, code_changes: By block access index (ascending)

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 where post-value equals pre-value, also known as "no-op writes").

Note: Implementations MUST check the pre-transaction value to correctly distinguish between actual writes and no-op writes.

Balance (balance_changes)

Record post‑transaction balances (uint128) for:

• Transaction senders (gas + value).
• Transaction recipients (only if value > 0).
• CALL/CALLCODE senders (value).
• CALL/CALLCODE recipients (only if value > 0).
• CREATE/CREATE2 recipients (only if value > 0).
• Coinbase (rewards + fees).
• SELFDESTRUCT/SENDALL beneficiaries.
• Withdrawal recipients (system withdrawals, EIP-4895).

For unaltered account balances:

If an account’s balance changes during a transaction, but its post-transaction balance is equal to its pre-transaction balance, then the change MUST NOT be recorded in balance_changes. The sender and recipient address (including the coinbase) MUST be included in AccountChanges.

This includes the following special cases where addresses MUST be included with empty changes if no other state changes occur. This includes:

• Zero-value transfer recipients
• Calling a same-transaction SELFDESTRUCT on an address that had a zero pre-transaction balance

Zero-value block reward recipients MUST NOT trigger a balance change in the block access list and MUST NOT cause the recipient address to be included as a read (e.g. without changes). Zero-value block reward recipients MUST only be included with a balance change in blocks where the reward is greater than zero.

Code

Track post‑transaction runtime bytecode for deployed or modified contracts, and delegation indicators for successful delegations 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)

• Precompiled contracts: Precompiles MUST be included when accessed. If a precompile receives value, it is recorded with a balance change. Otherwise, it is included with empty change lists.
• SENDALL: For positive-value selfdestructs, the sender and beneficiary are recorded with a balance change.
• SELFDESTRUCT (in-transaction): Accounts destroyed within a transaction MUST be included in AccountChanges without nonce or code changes. However, if the account had a positive balance pre-transaction, the balance change to zero MUST be recorded. Storage keys within the self-destructed contracts that were modified or read MUST be included as a storage_read.
• Accessed but unchanged: Include the address with empty changes (e.g., targets of EXTCODEHASH, EXTCODESIZE, BALANCE, STATICCALL, etc.).
• Zero‑value transfers / Unchanged balance in transaction: 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. State changes from the reverted call are discarded, but all accessed addresses MUST be included. If no changes remain, addresses are included with empty lists; if storage was read, the corresponding keys MUST appear in storage_reads.
• 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-7702 Delegations: The authority address MUST be included with the nonce and code changes after any successful delegation set, reset, or update. Additionally it MUST be included with an empty change set if authorization fails, but the authority address has already been added to accessed_addresses (as defined in EIP-2929). The delegation target MUST NOT be included during delegation creation and MUST be included when loaded as a call target under authority execution.
• 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 Engine API is extended with new structures and methods to support block-level access lists:

ExecutionPayloadV4 extends ExecutionPayloadV3 with:

• blockAccessList: RLP-encoded block access list

engine_newPayloadV5 validates execution payloads:

• Accepts ExecutionPayloadV4 structure
• Validates that computed access list matches provided blockAccessList
• Returns INVALID if access list is malformed or doesn't match

engine_getPayloadV6 builds execution payloads:

• Returns ExecutionPayloadV4 structure
• Collects all account accesses and state changes during transaction execution
• Populates blockAccessList field with RLP-encoded access list

The execution layer provides the RLP-encoded blockAccessList to the consensus layer via the Engine API. The consensus layer then computes the SSZ hash_tree_root for storage in the ExecutionPayloadHeader.

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 MAY validate by comparing execution-gathered accesses 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.