How Scroll Blockchain Works: Technical Details and Architecture Overview

Introduction

Scroll is a Layer 2 (L2) blockchain solution designed to scale Ethereum using ZK-Rollups (Zero-Knowledge Rollups). Developed in collaboration with the Ethereum Foundation's Privacy and Scaling Explorations group, Scroll bundles transactions off-chain and submits cryptographic proofs to Ethereum (L1), ensuring security while reducing costs and congestion.

This guide explores Scroll’s architecture, workflow, and key components, including:

• Centralized sequencing nodes (Execution Node, Rollup Node).
• Decentralized proving networks (Roller Net).
• The rollup process and transaction lifecycle.

Core Technical Principles

Scroll’s design is influenced by Ethereum’s scalability challenges and ZKP (Zero-Knowledge Proof) advancements. Key principles include:

• EVM Compatibility: Supports existing Ethereum smart contracts with minor adjustments.
• Data Availability: All transaction data is stored on L1 for transparency.
• Decentralized Proving: Proofs are generated by a network of validators (Provers).

Architecture Overview

Scroll’s architecture comprises four layers:

1. Settlement Layer (L1 Ethereum)

• Bridge Contract: Facilitates asset/message transfers between L1 and L2.

• Rollup Contract:

  • Verifies transaction batches.
  • Ensures data availability.
  • Orders transactions for the canonical chain.

2. Sequencing Layer

• Execution Node:

  • Processes L2 transactions.
  • Creates L2 blocks.

• Rollup Node:

  • Bundles transactions into batches.
  • Submits data and proofs to L1.

3. Proving Layer

• Provers: Generate ZK proofs for transaction validity.
• Coordinator: Assigns proof tasks to Provers randomly.

4. Rollup Process

1. Execution: Transactions are processed into L2 blocks.
2. Batching: Blocks are grouped into chunks/batches.
3. Finalization: Proofs are submitted to L1 for verification.

Rollup Workflow

Stage 1: Transaction Execution

1. Users submit transactions via L1 Bridge or L2 mempool.
2. Sync Service (Execution Node) retrieves L1 transactions.
3. The Executor creates L2 blocks.

Stage 2: Batch Creation

4. Rollup Node extracts L2 block data.
5. Chunk/Batch Proposer packages transactions.
6. Relayer submits batch data to L1 (Commit phase).

Stage 3: Proof Finalization

7. Coordinator requests proofs from Provers.
8. Verified proofs are recorded in the database.
9. Relayer submits proofs to L1 (Finalize phase).

Transaction Lifecycle

1. Confirmed: Executed in L2 but not yet posted to L1.
2. Committed: Data published to L1 (no validity proof).
3. Finalized: Proof verified on L1.

Key Features

Pros

• EVM Compatibility: Use existing tools (Hardhat, MetaMask).
• Low Fees: Reduced gas costs vs. L1.
• Fast Transactions: Instant L2 confirmations.

Cons

• Testing Overhead: Requires L2-specific audits.
• Centralization: Sequencers are currently centralized.

FAQ

Q1: Is Scroll fully compatible with Ethereum?
A: Yes, except for minor precompiled contract differences.

Q2: How long does finalization take?
A: Typically minutes, depending on L1 congestion.

Q3: Can I deploy existing Ethereum dApps on Scroll?
A: Yes, with minor adjustments.

Conclusion

Scroll’s innovative use of ZK-Rollups positions it as a leading Ethereum scaling solution. Its EVM compatibility and growing ecosystem (see here) make it ideal for developers prioritizing low-cost, high-speed transactions.

👉 Explore Scroll’s Ecosystem

For more on blockchain architecture, follow our Magazine.