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Ethereum Applications GuildEAG Developer Course

4. L2, Indexing, Security & Web3 Identity

Goal

Section titled “Goal”

Understand real application concerns beyond deployment, including L2s, indexing, identity, and basic security.

Module Guide

Section titled “Module Guide”

By now you can build and ship a full-stack dApp. Module 4 is about everything that separates a demo from something you’d actually put in front of users: it costs too much on mainnet, so you need L2s; the frontend needs to read history efficiently, so you need indexing; users need readable names and better sign-in, so you meet ENS and identity; accounts are getting smarter, so you meet account abstraction; and — most importantly — real contracts hold real money, so you take your first pass at security. The module is deliberately broad, and several lessons are short “explainer” videos meant to give you working vocabulary rather than deep implementation.

The scaling thread runs through several lessons. Gas, L2 & Multisig (22) connects network choice to cost and introduces multisig as an operational safety tool; Layer 2 Scaling Explained (24, by Finematics) gives the clean conceptual model of why rollups work; and Deploy First Contract on Arbitrum (30) makes it concrete by having you deploy to a real L2 testnet — the skill Lab 4 requires. The identity thread runs through ENS, DEX & Identity (23) and connects to sign-in-with-Ethereum. The frontier thread — ERC-4337 (25, account abstraction), EIP-7702 (26, smart-account behavior for EOAs), and x402 (27, onchain payments) — is conceptual context: know what these are and why they matter for UX, without needing to implement them.

The security thread is the one to take most seriously. The PasswordStore audit (28, an external Cyfrin Updraft chapter) walks you through finding a vulnerability in a small contract, and Burner Wallets (29) reinforces the operational habit of never mixing test keys with real funds. These feed directly into Lab 4’s central task: run an AI-assisted security review of your own contract and produce a security self-checklist. The common beginner risks — bad permissions, reentrancy, unsafe approve flows, price manipulation, leaked keys — are the things this module teaches you to look for.

By the end you should be able to explain what L2s are for and deploy to one, describe the role of ENS and account abstraction at a high level, read contract events into a frontend, and identify beginner-level security risks in a contract. That rounds out the “real application” picture before the Module 5 capstone.

Topics

Section titled “Topics”
  • Differences between L2s and mainnet
  • L2 testnet deployment
  • Basic indexing: events, The Graph, and Ponder concepts
  • SIWE
  • ERC-4337 roles and concepts
  • Common security risks: permissions, reentrancy, approve flows, price manipulation, and private key leakage

Assigned Lessons

Section titled “Assigned Lessons”

Open the Module 4 lesson sequence

Lab Tasks

Section titled “Lab Tasks”

Open Lab 4: Deploy and Review an L2 Application

  • Deploy to an L2 testnet
  • Read contract events and display them in the frontend
  • Ask an AI agent to perform a security review of the contract
  • Produce a security self-checklist

Learning Outcomes

Section titled “Learning Outcomes”

You will be able to

  • Summarize L2 use cases and major differences
  • Explain the basic roles of SIWE and ERC-4337
  • Deploy a dApp to an L2 testnet
  • Identify beginner-level smart contract security risks