Scroll Research

Pioneering the future of the Open Economy.

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8/ TL;DR

Subcommitments give rollups:

✅ Fast off-chain finality
✅ Strong security assumptions
✅ Flexible and efficient DA strategies

We thank @donnoh_eth for his helpful feedback on an initial draft of this post.

Read the complete article here:
https://t.co/SHHMiULwNG

[Scroll Research @scrollresearch]

1/ 🔒 Subcommitments: Off-Chain Finality — Fast, Secure, and Cheap

We introduce subcommitments, a new mechanism that boosts off-chain finality without sacrificing security or cost efficiency.

Let’s break it down 🧵👇

[Scroll Research @scrollresearch]

7/ Optimizing Finality & Cost

Subcommitments decouple data availability from finality.

Sequencers can publish full data later (e.g. when blob prices drop or compression is optimal) without compromising user confidence.

If sequencer fails to do so in a timely manner, anyone can publish consistent data with pending subcommitments and finalize the bridge.

[Scroll Research @scrollresearch]

14/ Rollups aren’t “just L2s”. They’re intricate systems blending L1 trust, off-chain execution, and user-centric design.

we would like to thank @donnoh_eth and @toghrulmaharram for their helpful feedback on an initial draft of this post.

Follow us for more research content and read the complete article in our research blog.
https://t.co/t7w0lpg91I

[Scroll Research @scrollresearch]

7/ The Prover
The brain of the bridge.

Generates:
💡 Validity proofs (ZK)
⚔️ Fraud proofs (Optimistic)

Critical for bridging, security, and sometimes compression (in SD-based rollups).

Decoupling sequencer & prover is hard, but vital for decentralization.

[Scroll Research @scrollresearch]

13/ Users care about one thing: UX.

Low fees, fast txs, instant feedback. They don’t care about rollup mechanics.

Designers must abstract away complexity while preserving security. And that’s not trivial.

[Scroll Research @scrollresearch]

6/ 🌉 The Bridge
Handles asset transfers between L1 and L2.

Deposits: custody on L1 → mint on L2
Withdrawals: burn on L2 → prove to L1 → release funds

Two kinds:
🔴 Optimistic: fraud-proof window
🔐 ZK/validity: validity proof required

[Scroll Research @scrollresearch]

1/🧵 What is a rollup? And how do you make sense of inboxes, sequencers, bridges, and proofs?

This thread breaks down "Rollups From First Principles" — a must-read by @jonastheis_ for anyone building or curious about L2s.

👇Let’s dive in.

https://t.co/b7Cw8pmQ8N

[Scroll Research @scrollresearch]

5/ The Sequencer

Acts fast, but trust is involved. Collects L2 txs, gives pre-confirmations to users. Batches and posts txs to L1. Can be centralized or decentralized.

🧠 Pre-conf ≠ finality.

Users relying on pre-conf are vulnerable to sequencer failures or attacks.

[Scroll Research @scrollresearch]

4/ 📪 The Inbox

It’s the gateway. All L2 inputs (L1 messages, batched L2 txs) go here. Usually sent directly to L1 or posted by a sequencer with some access control.

[Scroll Research @scrollresearch]

3/ Rollup flow at a high level

📨 Input: L2 tx data posted to L1 (calldata or blob)
⚙️ CDF: Derive L2 chain from L1 inputs
⚙️ STF: Apply tx to derive new L2 state
🧾 Output: Canonical L2 chain and state

The key? It’s deterministic. Every honest node arrives at the same result.

[Scroll Research @scrollresearch]

2/ Rollups are L2 protocols that inherit security and data availability from L1, but execute transactions off-chain for scale.

They rely on a few core components:
- Inbox
- Sequencer
- Prover
- Bridge
- L2 node

Each plays a unique role in maintaining the rollup’s state and integrity.