🙍Key Roles and Their Interactions

The ERC-4337 ecosystem introduces the UserOperation, a flexible alternative to typical Ethereum transactions.

UserOperation

It is like a blueprint that tells the system about a user's intended action. To avoid mix-ups, it's not just called a transaction, even though it shares similarities.

What does it have in common with regular transactions?

Just like a typical transaction, a UserOperation has details such as:

• sender: Who's initiating it.

• to: The recipient or destination.

• calldata: The action or operation to be performed.

• maxFeePerGas: The maximum gas fee.

• maxPriorityFee: Priority fee for faster processing.

• signature: A cryptographic proof of authenticity.

• nonce: A unique number to prevent replay attacks.

How is it different?

Apart from the common fields, a UserOperation contains additional unique fields which are explained separately.

The way the signature works in a UserOperation is unique. Instead of being pre-determined by the system, it's up to each individual account's rules to decide how it’s used.

In essence, while a UserOperation resembles a transaction in many ways, it also offers more flexibility and customization for users.

Sender

This refers to the client that initiates or sends out a UserOperation.

EntryPoint

A unique contract designed to process batches of UserOperations.

Bundlers or clients pick and choose which EntryPoint they want to work with, creating a whitelist of accepted EntryPoints.

Bundler (acting as the middleman, ensuring everything gets processed correctly into the blockchain)

A type of node (or system participant) that specializes in managing UserOperations.

Responsibilities:

• Take UserOperations and convert them into a valid action, known as EntryPoint.handleOps(), to be added to a blockchain block.

• There are several ways this can happen:

  1. A bundler might take on the role of a block builder itself.

  2. If the bundler isn't acting as a block builder, it has to work in tandem with established block-building systems, like mev-boost or any other system that separates block proposal from block building (called PBS).

  3. Alternatively, a bundler can utilize an experimental system, if available, known as eth_sendRawTransactionConditional RPC API.

Aggregator (that assists in ensuring multiple signatures are legitimate)

A supportive contract that accounts rely on, especially to verify combined or aggregated signatures.

Just as with the EntryPoint, bundlers or clients create a whitelist for the aggregators they trust and want to work with.

Recap

In simpler terms, when using the UserOperation system, you have:

• The Sender starting things off by initiating a UserOperation.

• The EntryPoint which is the go-to spot for processing groups of these operations.

• The Bundler acting as the middleman, ensuring everything gets processed correctly into the blockchain.

• And the Aggregator that assists in ensuring multiple signatures are legitimate.