EIP-8141 - Frame Transaction

Abstract

Add a new transaction whose validity and gas payment can be defined abstractly. Instead of relying solely on a single ECDSA signature, accounts may freely define and interpret their signature scheme using any cryptographic system.

Motivation

This new transaction provides a native off-ramp from the elliptic curve based cryptographic system used to authenticate transactions today, to post-quantum (PQ) secure systems.

In doing so, it realizes the original vision of account abstraction: unlinking accounts from a prescribed ECDSA key and support alternative fee payment schemes. The assumption of an account simply becomes an address with code. It leverages the EVM to support arbitrary user-defined definitions of validation and gas payment.

Specification

Constants

Opcodes

New Transaction Type

A new EIP-2718 transaction with type FRAME_TX_TYPE is introduced. Transactions of this type are referred to as "Frame transactions".

The payload is defined as the RLP serialization of the following:

[chain_id, nonce, sender, frames, max_priority_fee_per_gas, max_fee_per_gas, max_fee_per_blob_gas, blob_versioned_hashes]

frames = [[mode, target, gas_limit, data], ...]

If no blobs are included, blob_versioned_hashes must be an empty list and max_fee_per_blob_gas must be 0.

Modes

There are three modes:

DEFAULT Mode

Frame executes as regular call where the caller address is ENTRY_POINT.

VERIFY Mode

Identifies the frame as a validation frame. Its purpose is to verify that a sender and/or payer authorized the transaction. It must terminate execution with APPROVE. Any other result will cause the whole transaction to be invalid.

The execution behaves the same as STATICCALL, state cannot be modified.

Frames in this mode will have their data elided from signature hash calculation and from introspection by other frames.

SENDER Mode

Frame executes as regular call where the caller address is sender. This mode effectively acts on behalf of the transaction sender and can only be used after explicitly approved.

Constraints

Some validity constraints can be determined statically. They are outlined below:

assert tx.chain_id < 2**256
assert tx.nonce < 2**64
assert len(tx.frames) > 0 and len(tx.frames) <= MAX_FRAMES
assert len(tx.sender) == 20
assert tx.frames[n].mode < 3
assert len(tx.frames[n].target) == 20 or tx.frames[n].target is None

Receipt

The ReceiptPayload is defined as:

[cumulative_gas_used, payer, [frame_receipt, ...]]
frame_receipt = [status, gas_used, logs]

payer is the address of the account that paid the fees for the transaction. status is the return code of the top-level call.

Signature Hash

With the frame transaction, the signature may be at an arbitrary location in the frame list. In the canonical signature hash any frame with mode VERIFY will have its data elided:

def compute_sig_hash(tx: FrameTx) -> Hash:
    for i, frame in enumerate(tx.frames):
        if frame.mode == VERIFY:
            tx.frames[i].data = Bytes()
    return keccak(rlp(tx))

New Opcodes

APPROVE opcode (0xaa)

The APPROVE opcode is like RETURN (0xf3). It exits the current context successfully, but with a status code beyond the traditional 0 fail and 1 success via the scope operand.

Stack

Scope Operand

The scope operand must be one of the following values:

1. 0x0: Approval of execution - the sender contract approves future frames calling on its behalf. Only valid when frame.target equals tx.sender.
2. 0x1: Approval of payment - the contract approves paying the total gas cost for the transaction.
3. 0x2: Approval of execution and payment - combines both 0x0 and 0x1.

Any other value results in an exceptional halt.

Status Code

The status of a call returning with APPROVE has three new potential status codes.

Note: codes 0 and 1 already exist today and are replicated here for completeness.

TXPARAM* opcodes

The TXPARAMLOAD (0xb0), TXPARAMSIZE (0xb1), and TXPARAMCOPY (0xb2) opcodes follow the pattern of CALLDATA* / RETURNDATA* opcode families. Gas cost follows standard EVM memory expansion costs.

Each TXPARAM* opcode takes two extra stack input values before the CALLDATA* equivalent inputs. The values of these inputs are as follows:

Notes:

• 0x03 and 0x04 have a possible future extension to allow indices for multidimensional gas.
• The status field (0x15) returns 0 for failure or 1 for success.
• Out-of-bounds access for frame index (>= len(frames)) and blob index results in an exceptional halt.
• Invalid in1 values (not defined in the table above) result in an exceptional halt.
• The data field (0x12) returns size 0 value when called on a frame with VERIFY set.

Behavior

When processing a frame transaction, perform the following steps.

Perform stateful validation check:

• Ensure tx.nonce == state[tx.sender].nonce

Initialize with transaction-scoped variables:

• payer_approved = false
• sender_approved = false

Then for each call frame:

1. Execute a call with the specified mode, target, gas_limit, and data.
2. If target is null, set the call target to tx.sender.
3. If mode is SENDER:
   • sender_approved must be true. If not, the transaction is invalid.
   • Set caller as tx.sender.
4. If mode is DEFAULT or VERIFY:
   • Set the caller to ENTRY_POINT.
5. The ORIGIN opcode returns frame caller throughout all call depths.
6. If the frame exits with 1 < status < 5, update approval state:
7. 2 (execution approval): If target = tx.sender, set sender_approved = true.
   • If sender_approved is already set, revert the frame.
8. 3 (payment approval): If payer_approved is false, increment the sender's nonce, collect the total gas cost of the transaction from target, and set payer_approved = true.
   • If target has insufficient balance, the transaction is invalid.
   • If sender_approved == false and status is 3, revert the frame.
   • If sender_approved == true and status is 4, revert the frame.
9. 4 (both): Apply rule for status 2 then for status 3.
10. If frame has mode VERIFY and the frame did not terminate with status 1 < status < 5, the transaction is not valid.

After executing all frames, verify that payer_approved == true. If it is, refund any unpaid gas to the gas payer. If it is not, the whole transaction is invalid.

Note: it is implied by the handling that the sender must approve the transaction before the payer and that once sender_approved or payer_approved become true they cannot be re-approved or reverted.

Frame interactions

A few cross-frame interactions to note:

• For the purposes of gas accounting of warm / cold state status, the journal of such touches is shared across frames.
• Discard the TSTORE and TLOAD transient storage between frames.

Gas Accounting

The total gas limit of the transaction is:

tx_gas_limit = FRAME_TX_INTRINSIC_COST + calldata_cost(rlp(tx.frames)) + sum(frame.gas_limit for all frames)

Where calldata_cost is calculated per standard EVM rules (4 gas per zero byte, 16 gas per non-zero byte).

The total fee is defined as:

tx_fee = tx_gas_limit * effective_gas_price + blob_fees
blob_fees = len(blob_versioned_hashes) * GAS_PER_BLOB * blob_base_fee

The effective_gas_price is calculated per EIP-1559 and blob_fees is calculated as per EIP-4844.

Each frame has its own gas_limit allocation. Unused gas from a frame is not available to subsequent frames. After all frames execute, the gas refund is calculated as:

refund = sum(frame.gas_limit for all frames) - total_gas_used

This refund is returned to the gas payer (the target that called APPROVE(0x1) or APPROVE(0x2)) and added back to the block gas pool. Note: This refund mechanism is separate from EIP-3529 storage refunds.

Rationale

Canonical signature hash

The canonical signature hash is provided in TXPARAMLOAD to simplify the development of smart accounts.

Computing the signature hash in EVM is complicated and expensive. While using the canonical signature hash is not mandatory, it is strongly recommended. Creating a bespoke signature requires precise commitment to the underlying transaction data. Without this, it's possible that some elements can be manipulated in-the-air while the transaction is pending and have unexpected effects. This is known as transaction malleability. Using the canonical signature hash avoids malleability of the frames other than VERIFY.

The frame.data of VERIFY frames is elided from the signature hash. This is done for two reasons:

1. It contains the signature so by definition it cannot be part of the signature hash.
2. In the future it may be desired to aggregate the cryptographic operations for data and compute efficiency reasons. If the data was introspectable, it would not be possible to aggregate the verify frames in the future.
3. For gas sponsoring workflows, we also recommend using aVERIFY frame to approve the gas payment. Here, the input data to the sponsor is intentionally left malleable so it can be added onto the transaction after the sender has made its signature. Notably, the frame.target of VERIFY frames is covered by the signature hash, i.e. the sender chooses the sponsor address explicitly.

Payer in receipt

The payer cannot be determined statically from a frame transaction and is relevant to users. The only way to provide this information safely and efficiently over the JSON-RPC is to record this data in the receipt object.

No authorization list

The EIP-7702 authorization list heavily relies on ECDSA cryptography to determine the authority of accounts to delegate code. While delegations could be used in other manners later, it does not satisfy the PQ goals of the frame transaction.

No access list

The access list was introduced to address a particular backwards compatibility issue that was caused by EIP-2929. The risk-reward of using an access list successfully is high. A single miss, paying to warm a storage slot that does not end up getting used, causes the overall transaction cost to be greater than had it not been included at all.

Future optimizations based on pre-announcing state elements a transaction will touch will be covered by block level access lists.

No value in frame

It is not required because the account code can send value.

Examples

Example 1: Simple Transaction

Frame 0 verifies the signature and exits with APPROVE(0x2) to approve both execution and payment. Frame 1 executes and exits normally via RETURN.

The mempool can process this transaction with the following static validation and call:

• Verify that the first frame is a VERIFY frame.
• Verify that the call of frame 0 succeeds, and does not violate the mempool rules (similar to ERC-7562).

Example 1a: Simple ETH transfer

A simple transfer is performed by instructing the account to send ETH to the destination account. This requires two frames for mempool compatibility, since the validation phase of the transaction has to be static.

This is listed here to illustrate why the transaction type has no built-in value field.

Example 1b: Simple account deployment

This example illustrates the initial deployment flow for a smart account at the sender address. Since the address needs to have code in order to validate the transaction, the transaction must deploy the code before verification.

The first frame would call a deployer contract, like EIP-7997. The deployer determines the address in a deterministic way, such as by hashing the initcode and salt. However, since the transaction sender is not authenticated at this point, the user must choose an initcode which is safe to deploy by anyone.

Example 2: Sponsored Transaction (Fee Payment in ERC-20)

• Frame 0: Verifies signature and exits with APPROVE(0x0) to authorize execution from sender.
• Frame 1: Checks that the user has enough ERC-20 tokens, and that the next frame is an ERC-20 send of the right size to the sponsor. Exits with APPROVE(0x1) to authorize payment.
• Frame 2: Sends tokens to sponsor.
• Frame 3: User's intended call.
• Frame 4 (optional): Check unpaid gas, refund tokens, possibly convert tokens to ETH on an AMM.

Data Efficiency

Basic transaction sending ETH from a smart account:

Notes: Nonce assumes < 65536 prior sends. Fees assume < 1099 gwei. Validation frame target is 1 byte because target is tx.sender. Validation gas assumes <= 65,536 gas. Calldata is 65 bytes for ECDSA signature. Blob fields assume no blobs (empty list, zero max fee).

This is not much larger than an EIP-1559 transaction; the extra overhead is the need to specify the sender and amount in calldata explicitly.

First transaction from an account (add deployment frame):

Notes: Gas assumes cost < 2^24. Calldata assumes small proxy.

Trustless pay-with-ERC-20 sponsor (add these frames):

Notes: Sponsor can read info from other fields. ERC-20 transfer call is 68 bytes.

There is some inefficiency in the sponsor case, because the same sponsor address must appear in three places (sponsor validation, send to sponsor inside ERC-20 calldata, post op frame), and the ABI is inefficient (~12 + 24 bytes wasted on zeroes). This is difficult to mitigate in a "clean" way, because one of the duplicates is inside the ERC-20 call, "opaque" to the protocol. However, it is much less inefficient than ERC-4337, because not all of the data takes the hit of the 32-byte-per-field ABI overhead.

Backwards Compatibility

The ORIGIN opcode behavior changes for frame transactions, returning the frame's caller rather than the traditional transaction origin. This is consistent with the precedent set by EIP-7702, which already modified ORIGIN semantics. Contracts that rely on ORIGIN = CALLER for security checks (a discouraged pattern) may behave differently under frame transactions.

Security Considerations

Transaction Propagation

Frame transactions introduce new denial-of-service vectors for transaction pools that node operators must mitigate. Because validation logic is arbitrary EVM code, attackers can craft transactions that appear valid during initial validation but become invalid later. Without any additional policies, an attacker could submit many transactions whose validity depends on some shared state, then submit one transaction that modifies that state, and cause all other transactions to become invalid simultaneously. This wastes the computational resources nodes spent validating and storing these transactions.

Example Attack

A simple example is transactions that check block.timestamp:

function validateTransaction() external {
    require(block.timestamp < SOME_DEADLINE, "expired");
    // ... rest of validation
    APPROVE(0x2);
}

Such transactions are valid when submitted but become invalid once the deadline passes, without any on-chain action required from the attacker.

Mitigations

Node implementations should consider restricting which opcodes and storage slots validation frames can access, similar to ERC-7562. This isolates transactions from each other and limits mass invalidation vectors.

It's recommended that to validate the transaction, a specific frame structure is enforced and the amount of gas that is expended executing the validation phase must be limited. Once the frame exits with APPROVE(0x2), it can be included in the mempool and propagated to peers safely.

For deployment of the sender account in the first frame, the mempool must only allow specific and known deployer factory contracts to be used as frame.target, to ensure deployment is deterministic and independent of chain state.

In general, it can be assumed that handling of frame transactions imposes similar restrictions as EIP-7702 on mempool relay, i.e. only a single transaction can be pending for an account that uses frame transactions.

Copyright

Copyright and related rights waived via CC0.