Nitro Testnet

TL;DR

The Espresso Network is a confirmation layer that provides chains with information about the state of their own chain and the states of other chains, which is important for cross-chain composability. Espresso confirmations can be used in addition to the soft confirmations from a centralized sequencer, are backed by the security of the Espresso Network, and are faster than waiting for Ethereum finality (12-15 minutes).

Overview

Purpose

This document describes how the Espresso Network provides fast confirmations to Arbitrum Orbit chains. Espresso has developed a TEE based integration, which is ready for chain operators and rollup-as-a-service providers to implement. There is some assumed familiarity with the Arbitrum Nitro stack.

How It Works

In a regular chain, the transaction lifecycle will look something like this:

1. A user transacts on an Arbitrum chain.

2. The transaction is processed by the chain’s sequencer, which provides a soft-confirmation to the user, and the transactions are packaged into a block.

3. The sequencer, responsible for collecting these blocks, compressing, and submitting, submits the transactions to the base layer.

   1. If the base layer is Arbitrum One or Ethereum, then the transaction will take at least 12-15 minutes to finalize, or longer depending on how frequently the sequencer posts to the base layer.

   2. In this transaction lifecycle, the user must trust that the chain’s sequencer provided an honest soft-confirmation and will not act maliciously. There are limited ways to verify that the sequencer and batcher acted honestly or did not censor transactions.

This is a strong assumption, and the key thing that the Espresso Network helps with. When the chain is integrated with the Espresso Network: The sequencer provides a soft-confirmation to the user, while the transactions are also sent to the Espresso Network to provide a stronger confirmation secured by BFT consensus. A software component of the sequencer called the batch poster (henceforth referred to as “batcher”) is run inside a TEE and must honor the Espresso Network confirmation. It cannot change the ordering or equivocate. This gives a strong guarantee that the transaction will ultimately be included and finalized by the base layer.

The user must trust that the chain’s sequencer provided an honest soft-confirmation; however the Espresso Network provides a stronger confirmation that keeps the sequencer accountable and prevents the sequencer from equivocating or acting maliciously. The initial implementation of the batch poster is permissioned and the user must trust that it will not reorder blocks produced by the sequencer.

Integration

Integrating with the Espresso Network requires minimal changes to Arbitrum Nitro’s existing rollup design. The Espresso Team has already done that, and in the following sections we will provide a comprehensive guide for running your own instance and building on Espresso!

Components

We model the rollup as a collection of three components:

• The sequencer

• The batcher

• The TEE contract

Transaction Flow

Chain Config