This ERC proposes a form of account abstraction (AA) that ensures compatibility with existing smart contract wallets and provides flexibility for alternative designs while avoiding introducing changes to the consensus layer. Instead of defining a strict structure for AA transactions, this proposal introduces the figure of endorser contracts. These smart contract instances are tasked with determining the quality of the submitted AA transactions, thus safely helping bundlers determine if a transaction should be kept in the mempool or not. Developers that intend to make their smart contract wallet compatible with this ERC must create and deploy an instance of an endorser or use an existing one compatible with their wallet.
This account abstraction proposal aims to implement a generalized system for executing AA transactions while maintaining the following goals:
To avoid Ethereum consensus changes, we do not attempt to create new transaction types for account-abstracted transactions. Instead, AA transactions are packed up in a struct called Operation, operations are structs composed by the following fields:
| Field | Type | Description |
|---|---|---|
| entrypoint | address | Contract address that must be called with callData to execute the operation. |
| callData | bytes | Data that must be passed to the entrypoint call to execute the operation. |
| fixedGas | uint64 | Amount of gas that the operation will pay for, regardless execution costs, and independent from gasLimit. |
| gasLimit | uint64 | Minimum gasLimit that must be passed when executing the operation. |
| feeToken | address | Contract address of the token used to repay the bundler. (address(0) for the native token). |
| endorser | address | Address of the endorser contract that should be used to validate the operation. |
| endorserCallData | bytes | Additional data that must be passed to the endorser when calling isOperationReady(). |
| endorserGasLimit | uint64 | Amount of gas that should be passed to the endorser when validating the operation. |
| maxFeePerGas | uint256 | Max amount of basefee that the operation execution is expected to pay. (Similar to EIP-1559 max_fee_per_gas). |
| priorityFeePerGas | uint256 | Fixed amount of fees that the operation execution is expected to pay to the bundler. (Similar to EIP-1559 max_priority_fee_per_gas). |
| feeScalingFactor | uint256 | Scaling factor to convert the computed fee into the feeToken unit. |
| feeNormalizationFactor | uint256 | Normalization factor to convert the computed fee into the feeToken unit. |
| hasUntrustedContext | bool | If true, the operation may have untrusted code paths. These should be treated differently by the bundler (see untrusted environment). |
| chainId | uint256 | Chain ID of the network where the operation is intended to be executed. |
These Operation objects can be sent to a dedicated operations mempool. A specialized class of actors called bundlers (either block producers running special-purpose code, or just users that can relay transactions to block producers) listen for operations on the mempool and execute these transactions.
Transactions are executed by calling the entrypoint with the provided callData. The entrypoint can be any contract, but most commonly it will be the wallet contract itself. Alternatively it can be an intermediary utility that deploys the wallet and then performs the transaction.
Mempool participants need to be able to able to filter "good operations" (operations that pay the bundler the defined fee) from "bad operations" (operations that either miss payment or revert altogether).
This categorization is facilitated by the endorser; the endorser must be a deployed smart contract that implements the following interface:
Endorsers SHOULD be registered in the EndorserRegistry with an amount of burned ETH.
The amount of ETH to be burned is not specified in this proposal as mempool operators are free to set their own minimum thresholds.
Mempool operators MAY accept operations from endorsers without any burned ETH, but they would increase their risk exposing themselves to denial of service attacks.
Mempool operators MAY publish the minimum amount of burned ETH required for each endorser.
To check for operation status, the caller must first call simulationSettings to retrieve a list of on chain alterations.
Then call when the isOperationReady method is called, the endorser must return this information:
true, it means the transaction MUST be executed correctly and the bundler MUST be paid the offered gas fees (even if the underlying intent of the operation fails).maxBlockNumber and maxBlockTimestamp are used as global constraints.The information provided by the endorser helps the mempool operator maintain a pool of "good" AA transactions that behave correctly; but it only provides a soft guarantee that the transaction will be executed correctly. Bundlers must always simulate the result of the execution before including a transaction in a block.
If the result of a simulation fails and the endorser still returns readiness == true with the same dependencies, then the endorser can not be trusted and it MUST be banned by the mempool operator.
The dependency list serves as a shortcut for the bundler to know which operations are fully independent from each other. This shortcut is useful for (a) clearing the mempool from operations that are no longer valid, and (b) for bundlers to know which operations can be included in the same block.
For efficiency, additional information MAY be provided to the endorser with endorserCallData.
If used, the endorser MUST validate that the provided endorserCallData is valid and relevant to the other values provided.
While the endorser is deployed on chain, calls to the endorser MUST NOT be submitted on chain. The bundler MUST read the results of simulationSettings, perform chain alterations and simulate the execution off chain.
| Field | Type | Description |
|---|---|---|
| baseFee | bool | true if the block.basefee should be considered a dependency. |
| blobBaseFee | bool | true if the block.blockbasefee should be considered a dependency. |
| chainId | bool | true if the block.chainid should be considered a dependency. |
| coinbase | bool | true if the block.coinbase should be considered a dependency. |
| difficulty | bool | true if the block.difficulty should be considered a dependency. |
| gasLimit | bool | true if the block.gaslimit should be considered a dependency. |
| number | bool | true if the block.number should be considered a dependency. |
| timestamp | bool | true if the block.timestamp should be considered a dependency. |
| txOrigin | bool | true if the tx.origin should be considered a dependency. |
| txGasPrice | bool | true if the tx.gasprice should be considered a dependency. |
| maxBlockNumber | uint256 | The maximum value of block.number that readiness applies to. |
| maxBlockTimestamp | uint256 | The maximum value of block.timestamp that readiness applies to. |
The endorser MUST use the maxBlockNumber and maxBlockTimestamp fields to limit the validity of the readiness result. This is useful for operations that are only valid for a certain period of time.
Note that all values are inclusive. If the endorser determines the validity of the operation is indefinite, the maxBlockNumber and maxBlockTimestamp fields MUST be set to type(uint256).max.
| Field | Type | Description |
|---|---|---|
| addr | address | Contract address of the dependencies entry. (Only one entry per address is allowed). |
| balance | bool | true if the balance of addr should be considered a dependency of the operation. |
| code | bool | true if the code of addr should be considered a dependency of the operation. |
| nonce | bool | true if the nonce of addr should be considered a dependency of the operation. |
| allSlots | bool | true if all storage slots of addr should be considered a dependency of the operation. |
| slots | bytes32[] | List of all storage slots of addr that should be considered dependencies of operation. |
| constraints | Constraint[] | List of storage slots of addr that have a range of specific values as dependencies. |
The endorser does not need to include all accessed storage slots on the dependencies list, it only needs to include storage slots that after a change may also result in a change of readiness.
Note that allSlots, constraints and slots are mutually exclusive. If allSlots is set to true, then constraints and slots MUST be empty arrays.
If a slot is listed in constraints, it MUST NOT be listed in slots.
The endorser should prefer to use constraints over slots, and slots over allSlots whenever possible to limit reevaluation requirements of the bundler.
E.g. A wallet may pay fees using funds stored as WETH. During
isOperationReady(), the endorser contract may call thebalanceOfmethod of theWETHcontract to determine if the wallet has enoughWETHbalance. Even though the ETH balance of the WETH contract and the code of the WETH contract are being accessed, the endorser only cares about the user's WETH balance for this operation and hence does not include these as dependencies.
| Field | Type | Description |
|---|---|---|
| slot | bytes32 | Storage slot of addr that has a range of specific values as dependencies. |
| minValue | bytes32 | Minimum value (inclusive) of slot that readiness applies to. |
| maxValue | bytes32 | Maximum value (inclusive) of slot that readiness applies to. |
The endorser can use the minValue and maxValue fields to limit the validity of the readiness result. This allows the endorser to fully validate an operation, even when this operation depends on storage values that are not directly accessible by the endorser.
Note that all values are inclusive. When an exact value is required, minValue and maxValue should be set to the same value.
The simulationSettings method returns a list of replacements that the bundler should apply to the operation before simulating the isOperationReady. Note that these replacements are only used for isOperationReady simulation and are not applied when simulating the operation itself.
| Field | Type | Description |
|---|---|---|
| oldAddr | address | The on chain address where contract code is currently located. |
| newAddr | address | The address the contract code should be located when performing simulation. |
| slots.slot | bytes32 | The slot location to be changed. |
| slots.value | bytes32 | The value of the slot to be set before performing simulation. |
The endorser MAY use the simulationSettings method to provide a list of replacements that the bundler should apply to the network before simulating isOperationReady. This is useful for operations that must be called from specific contract addresses or that depend on specific storage values (e.g. ERC-4337's EntryPoint).
The endorser MAY provide it's own address for replacement. In this event, the bundler should update the endorser address used when calling isOperationReady.
It is possible for endorser contracts to behave maliciously or erratically in the following ways:
true to false while none of the dependencies register any change.The bundler MUST discard and re-evaluate the readiness status after a change on any of the dependencies of the operation, meaning that only operations considered ready are candidates for constructing the next block.
If, when simulating the final inclusion of the operation, the bundler discovers that it does not result in correct payment (either because the transaction fails, or transferred amount is below the defined fee), then it MUST ban the endorser.
When an endorser is banned, the mempool operator MUST drop all operations related to the endorser.
In some scenarios, the endorser may not be able to fully validate the operation but may be able to infer that a given code path should be safe. In these cases, the endorser can mark a section of the operation as untrusted. Any storage slots (balance, code, nonce, or specific slots) accessed in this untrusted context should be automatically considered as dependencies.
The endorser can use the UntrustedStarted and UntrustedEnded events to signal the start and end of an untrusted context. The bundler should listen to these events and extend the dependencies list accordingly.
Only the top-level endorser can signal an untrusted context; any other events with the same signature but emitted by a different contract should be ignored.
Untrusted contexts can be opened and closed multiple times and can be nested. If multiple events are emitted, the bundler MUST count the number of UntrustedStarted and UntrustedEnded events and only consider the untrusted context as ended when the number of UntrustedEnded events is equal to the number of UntrustedStarted events.
If hasUntrustedContext is set to false, the bundler should ignore any UntrustedStarted and UntrustedEnded events.
All code executed within the untrusted context must be monitored. If the code executes any of the following opcodes, the dependency graph must be extended accordingly.
| Opcode | Dependency |
|---|---|
| BALANCE | dependencies[addr].balance = true |
| ORIGIN | global.txOrigin = true |
| CODESIZE | None |
| CODECOPY | None |
| GASPRICE | global.txGasPrice = true |
| EXTCODESIZE | dependencies[addr].code = true |
| EXTCODECOPY | dependencies[addr].code = true |
| EXTCODEHASH | dependencies[addr].code = true |
| COINBASE | global.coinbase = true |
| TIMESTAMP | global.timestamp = true |
| NUMBER | global.number = true |
| DIFFICULTY | global.difficulty = true |
| PREVRANDAO | global.difficulty = true |
| CHAINID | global.chainId = true |
| SELFBALANCE | dependencies[self].balance = true |
| BASEFEE | global.baseFee = true |
| SLOAD | dependencies[addr].slots[slot] = true |
| CREATE | dependencies[addr].nonce = true |
| CREATE2 | dependencies[contract].code = true |
Notice that untrusted contexts generate a lot of dependencies and may generate many false positives. This may lead to numerous re-evaluations and thus to the operation being dropped from the mempool. A bundler MAY choose to drop operations if the number of dependencies exceeds a certain threshold.
Block-level dependencies are specially sensitive as they will be shared with a large number of operations.
It is recommended to use untrusted contexts only when necessary, like when an endorser needs to validate a nested signature to a wallet that is not under its control.
The endorser MUST guarantee that the operation will repay at least the spent gas to tx.origin.
The payment is always made in the feeToken, which can be any token standard (E.g. ERC-20). If feeToken is address(0), then payment is made in the native currency. When feeToken is address(0), feeScalingFactor and feeNormalizationFactor MUST be equal to 1.
All units are expressed in the native token unit. The result of the fee calculation is then converted to the feeToken unit using the feeScalingFactor and feeNormalizationFactor.
The gas units consider a fixed amount of gas (fixedGas) and a variable amount of gas (gasLimit). Allowing fixed costs caters for gas overheads which may be outside the scope of the on chain execution, such as calldata fees. This also allows repayment to be reduced when execution is cheaper than expected (such as when an inner call fails without reverting the top-level transaction), while still repaying the bundler.
The expected gas repayment is calculated as follows:
While the endorser MUST guarantee the repayment of expectedRepayment, the actual repayment amount MAY exceed this fee. E.g. For ease of development, a bundler MAY choose to only endorse operations that repay the maximum values provided by the operation.
Operations can be identified by their operation hash, which is calculated as a CIDv1 multihash of a raw file, containing the canonical JSON representation of the operation. This hash is never used on-chain, but it serves as a unique pointer to the operation that can be shared across systems.
The operation MAY be pinned on the IPFS network; this would allow other participants to retrieve the content of the operation after the operation has been removed from the mempool. This pinning is not mandatory, and it may be performed by the mempool operator or by the wallet itself if visibility of the operation is desired.
Bundlers can add their own rules for how to ensure the successful relaying of AA transactions and for getting paid for relaying these transactions. However, we propose here a baseline specification that should be sufficient.
When a bundler receives an operation, it SHOULD perform these sanity checks:
endorserGasLimit is sufficiently low (<= MAX_ENDORSER_GAS).MIN_ENDORSER_BURN), and (ii) it has not been internally flagged as banned.fixedGas is large enough to cover the cost associated with submitting the transaction (i.e. calldata gas costs).gasLimit is at least the cost of a CALL with a non-zero value.feeToken is address(0) or a known token address that the bundler is willing to accept.feeScalingFactor and feeNormalizationFactor are 1 for a feeToken value of address(0) or values the bundler is willing to accept.maxFeePerGas and priorityPerGas are above a configurable minimum value the bundler is willing to accept.maxFeePerGas and priorityFeePerGas of the newly received operation MUST be 12% higher than the one on the mempool to replace it. (Similar with how EOA with same nonce work)The bundler should then perform evaluation of the operation.
To evaluate the operation, the bundler MUST call simulationSettings() on the endorser to obtain simulation setting values. The bundler MUST apply the settings and simulate a call to isOperationReady() on the endorser. If the endorser considers the operation ready, and the constraints are within bounds, then the client MUST add the operation to the mempool. Otherwise, the operation MUST be dropped.
The endorser result SHOULD be invalidated and its readiness SHOULD be re-evaluated if any of the values of the provided dependencies change. If the operation readiness changes to false, the operation MUST be discarded.
Before including the operation in a block, a last simulation MUST be performed, this time by constructing the block and probing the result. All transactions in the block listed before the operation must be simulated and then the endorser must be queried for readiness in-case some dependencies changed. Then constraints MUST be re-evaluated for correctness. Finally, the operation MUST be simulated.
If the operation fails during the final simulation, the endorser MUST be banned because (i) it returned a bad readiness state or (ii) it changed the operation readiness independently from the dependencies.
Mempool clients MAY implement additional rules to further protect against maliciously constructed transactions.
MAX_OPERATION_DEPENDENCIES, dropping operations that cross the boundary.MAX_OPERATION_REEVALS, dropping operations that cross the boundary.If these rules are widely adopted, wallet developers should keep usage of dependencies to the lowest possible levels and avoid shared dependency slots that are frequently updated.
There is no limit in-place that defines that an operation can only be executed once.
The bundler SHOULD NOT drop an operation after successfully including such operation in a block, the bundler MAY perform evaluation.
If the endorser still returns readiness == true (after inclusion) then the operation SHOULD be treated as any other healthy operation, and thus it MAY be kept in the mempool.
The endorser registry serves as a place to register the burn of each endorser, anyone can increase the burn of any endorser by calling the addBurn() function.
All burn is effectively locked forever; slashing can't be reliably proved on-chain without protocol alterations, so it remains a virtual event on which mempool operators will ignore the deposited ETH.
(EXAMPLE)
The main challenge with a purely smart contract wallet-based account abstraction system is DoS safety: how can a bundler that includes an operation make sure it will be paid without executing the entire operation?
Bundlers could execute the entire operation to determine if it is healthy or not, but this operation may be expensive and complex for the following reasons:
gasLimit, exposing itself to a higher level of griefing.In this proposal, we add the endorser as a tool for the bundlers to validate arbitrary operations in a controlled manner, without the bundler having to know any of the inner workings of such operation.
In effect, we move the responsibility from the wallet to the wallet developer; the developer must code, deploy and burn ETH for the endorser; this is a nearly ideal scenario because developers know how their wallet operations work, and thus they can build tools to evaluate these operations efficiently.
Additionally, the specification is kept as simple as possible as enforcing a highly structured behavior and schema for smart contract wallet transactions may stagnate the adoption of more innovative types of wallets and the adoption of a shared standard among them.
Anyone can deploy a endorser contract and wallet clients are the one providing which endorser contract should be used for the given transaction. Instead of having each bundler rely on an off-chain registry that they need to maintain, the endorser registry can be called to see if the requested endorser contract is present and how much ETH was burned for it. Bundlers can then decide a minimum treshshold for how much ETH burnt is required for an endorser contract to be accepted. Bundlers are also free to support endorsers contract that are not part of the registry or are part of it but have no ETH burned associated.
Since the validation of an AA transactions is done off-chain by the bundler rather than at execution time, there is no additional gas fee overhead for executing transactions. The bundler bears the risk rather than all users having to pay for that security.
dependency.execution transactions from a trusted entrypoint contract, reducing overhead and allowing existing wallets to be compatible with the proposal.execution and signature payloads, this distinction remains implementation-specific.This ERC does not change he consensus layer, nor does impose changes on existing smart contract wallets, so there are no backwards compatibility issues.
This ERC does not make changes to on-chain interactions. Endorsers are explicitly for off-chain validations.
Bundlers are responsible for managing their own security and for ensuring that they are paid for the transactions they include in blocks.
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