3️⃣Aggregator

The core interface of the Aggregator contract is as follows:

interface IAggregator {
  function validateUserOpSignature(UserOperation calldata userOp) external view returns (bytes memory sigForUserOp);

  function aggregateSignatures(UserOperation[] calldata userOps) external view returns (bytes memory aggregatesSignature);

  function validateSignatures(UserOperation[] calldata userOps, bytes calldata signature) view external;
}

Working with Aggregators in the Ethereum System:

Using an Aggregator:

• An account can opt to use an aggregator to combine multiple signatures.

• If it does, when the system checks or "simulates" how a UserOp will be validated (using simulateValidation()), it will give a response called ValidationResultWithAggregator instead of just ValidationResult if something goes wrong.

Validating User Operations:

• Before accepting a UserOp, the bundler (special actor that packages multiple UserOps) must double-check the UserOp's authenticity using the validateUserOpSignature() method.

Aggregating Signatures:

• The method aggregateSignatures() is responsible for bringing all individual UserOp signatures together into one unified value.

Helper Methods:

• The methods mentioned above, like validateUserOpSignature() and aggregateSignatures(), are tools to assist the bundler.

• However, bundlers aren't strictly limited to these. They can choose to use their own libraries or tools to perform these validations and aggregations if they wish.

Final Signature Check:

• The method validateSignatures() is vital. It checks to ensure that the combined or "aggregated" signature is a perfect match for all the UserOps grouped together. If there's any discrepancy, the operation will stop or "revert".

• This critical check is done on-chain when the handleOps() method is called.

In a nutshell, when using an aggregator to handle multiple signatures, the system provides tools to ensure each step is verified and consolidated appropriately. Bundlers can use built-in methods or their own tools, but the final check always ensures everything matches up before processing.