Demystifying Scroll's technology stack and deal flow

Author: francesco, Castle Capital;

On October 10, Scroll released a mysterious message announcing the launch of the mainnet. While I didn't fully realize there was more to it than just airdrop farming, I decided to delve into it.

Scroll is a scaling solution for Ethereum, which is an L2 general-purpose zero-knowledge (zk) rollup. Let’s take a closer look at this technology.

As an L2 rollup running on Ethereum, Scroll imports native ETH security.

In addition to security, Scroll integrates seamlessly into the rich Ethereum ecosystem:

·Tools

· dApps

·Smart Contracts

·User Base

This approach enables effortless transfer and interchangeable use of these resources, ensuring unparalleled EVM compatibility. “For users and developers, Scroll is almost equivalent to Ethereum.”

Before the advent of Scroll, there was no universal zk rollup, mainly due to the calculation of generating zk for the Ethereum Virtual Machine (EVM) Proof complexity. Simply put, universal rollup is meant to have equivalent functionality to EVM.

However, successfully running an EVM environment on zk rollup has always been an elusive goal. This is due to the complexity of converting EVM transactions into logic circuits that can be explained through zk proofs. This complexity also explains why zk rollup projects only focus on specific applications, such as dYdX, which focuses on trading, and ImmutableX, which focuses on NFTs.

Due to technical difficulties, it is impossible to develop a universal network that can deploy various dAapps. This is also why zk-rollup performs poorly in terms of TVL and number of users compared to optimistic rollup (such as Immutable).

Despite these challenges, the search for universal zk rollup continues. Compatibility with EVM is important because it greatly simplifies the work required for developers to transition to the new chain.

The transition to a non-EVM chain means:

·Existing contracts must be migrated and rewritten to the new rollup.

·Not supported by existing EVM tools (libraries, wallets, markets, etc.).

·Unable to support applications from the Ethereum ecosystem.

Many rollups take on the task of universal zk EVM, with varying levels of EVM compatibility.

Comparison of the five major zkEVMs

(1) Starknet and zkSync (language level):

These are currently using their own customizations A dedicated solution for running virtual machines (Cairo VM). They ran a custom VM and created a compiler, the "Warp Transpiler", that compiled Solidity code into Cairo VM bytecode.

What they did was create a new VM and add Ethereum tool support on top as an extra layer. This still achieves the goal of exporting solidity contracts to StarkNet, thereby achieving "EVM compatibility".

Although not a direct EVM implementation, it retains compatibility and allows Solidity developers to write code for their rollups. This is a good compromise.

(2) Polygon zk-EVM (bytecode level):

Polygon runs a custom VM but has all EVM opcodes mapped to those valid for its VM. Polygon's approach is to build a zkEVM with "opcode-level equivalence".

Compared with Scroll, Polygon has an alternative runtime (runtime)-zkExecutor, which runs custom "zkASM" opcodes instead of running EVM opcodes directly. This is done to optimize EVM interpretation (since proving EVM directly would have too many limitations).

Here is a schematic diagram of this process:

While this configuration is more performant than Scroll, it adds a lot of custom code (to create zkASM ), introduces possible requirements to modify code or tooling to achieve compatibility, and may diverge more and more from Ethereum over time.

(3)Scroll (bytecode level):

Converts EVM execution directly into verifiable circuits, with advantages in tool support and compatibility. Currently, Scroll does not support all EVM opcodes, but they plan to eventually implement this over time.

#How does Scroll’s technology stack work?

Scroll is a zk rollup. There is a smart contract on ETH L1. It is a zkEVM proof validator that can verify whether the Scroll protocol is safe.

How do transactions proceed on Scroll?

·Scroll can batch process blocks and write block data to Ethereum.

·Once a proof of validity is generated in a new block, the proof is written to Ethereum.

Therefore, a block on a Scroll can have three states:

· Pre-commit: proposed by the sequencer and included in the Scroll.

·Committed: Transaction data published on Ethereum

·Finalized: Correct execution has been confirmed by an on-chain validity certificate published on Ethereum.

The transaction process is as follows:

(1) Transactions flowing in from the sequencer are bundled and packaged in a block (1).

(2) The data and call data are submitted to the rollup contract on L1, and the block is submitted (D1).

(3) Proof generation: Pass the information to the coordinator (the "trace" of the completed work), and then pass it to the prover, who then generates the zk proof.

(4) Proof generation can occupy multiple blocks and can be executed in parallel by different "provers".

# (5) Aggregation proof generation: Proofs are generated and aggregated in batches, and then submitted to the chain for verification (Verify).

(6) The block is finalized.

## Transactions > Processed by nodes running the Geth fork > Execution traces > Input to the zkEVM circuit > Generate proofs > Input into the set, indicating that the proof is valid The>Generate Aggregation Proof>is sent to L1 contract.

Why choose Scroll?

·Developer-centric: Provides bytecode equivalent to EVM.

·Efficiency: Create a more secure block space for Ethereum and reduce gas fees.

·Speed: Optimize block time (3 seconds vs. Ethereum’s 12 seconds).

·Consistent with Ethereum’s vision.

Since Scroll was released, more than $1.5 million in TVL has been accumulated.

More than 1,383 users have bridged ETH on Scroll.

Over 975 ETH have been bridged to the Scroll mainnet, totaling $1.5 million.

A few thoughts:

ZK rollup is seen as a design superior to its optimistic rollup competitors, especially in terms of privacy, due to No withdrawal delays due to lack of evidence of fraud.

As a bytecode-compatible universal zk rollup, Scroll promises to deliver the benefits of zk-proof on L2 without compromising the network effects and tooling of EVM.

Full compatibility with the EVM is the holy grail of L2, and that’s Scroll’s value proposition: Exciting Ethereum. Scroll's bytecode compatibility brings all the benefits of zk-proof to Ethereum with maximum compatibility.

It is also worth noting that Scroll is committed to achieving decentralization. While there will be a central orderer in the initial phase, plans for decentralization are in the works. Additionally, all ZK proofs will eventually be created by a decentralized "prover" network.

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