Scroll: A low-key challenger in the zkEVM race
Written by: Blockworks Research, Westie
Compiled by: Deep Tide TechFlow
Given that EVM is in the developer With the popularity of ZK, people have been hoping to combine the scalability of zk Rollup technology with the developer experience of EVM. This has led to an arms race of zkEVM systems in which the main players are Scroll, zkSync, and Polygon, with Scroll keeping a low profile relative to the other two.
Due to the limitations of the EVM, zkEVM faces a necessary trade-off between compatibility/equivalence and performance. Vitalik Buterin listed a scale from 1 to 4 in an effort to clarify the difference between the various zkEVM design choices:
Scroll is in the middle of this tradeoff: they are building a sort of 2.5 zkEVM.
This means they are equivalent to the EVM with very minor changes to the way the gas cost is structured.
What Makes Scroll Different
By keeping EVM equivalence, builders are able to directly migrate their applications from Ethereum L1 to Scroll without any modifications to their code. They are also fully open source, allowing anyone to use and verify their code.
Scroll also uses a fork of Geth for their sorter, allowing it to inherit the battle-tested system while Achieve the best compatibility with Ethereum.
This also means they can easily apply any new upgrades to Geth; other zkEVMs may require increased code complexity to upgrade.
Scroll Architecture
Scroll Architecture has three main Components: Scroll node, Roller network and verification bridge.
The purpose of the Scroll node is to build blocks from users' transactions and submit them to L1, as well as receive messages from L1.
The three main components of a Scroll Node are the Sequencer, Coordinator, and Repeater.
The orderer receives a batch of transactions from the L2 mempool and executes them to generate a new L2 block.
The block's execution trace is then sent to the coordinator, who passes it to a randomly chosen Roller to generate a proof.
The relayer monitors the state of the L2 blocks, their data availability and proof of validity from the rolling contract, and deposits and withdrawals from the bridge contract payment event to make sure everything can be verified.
The Roller network is responsible for generating proofs of validity. The Roller network will receive execution traces from the coordinator, send them to seven different proof circuits, aggregate them into one final circuit, and send the final block proof back to the coordinator.
Authentication Bridge Contains two contracts: Rollup contract and cross-chain bridge contract.
The cross-chain bridge contract handles the messages sent between L1 and L2, including the bridge transaction of ERC-20 Token.
Rollup contract receives and stores state root and block data as Ethereum state and calldata. Once a block proof has been verified by the Rollup contract, the block is considered finalized.
In general, after the orderer creates a block sequence and generates its proofs, multiple block proofs are aggregated into a single proof and sent by the coordinator to the Rollup contract, where the block is verified and finalized.
Roadmap
Scroll has been in Pre-Alpha testing for the past 3 months, including permissioned smart contract deployment and whitelisted user access.
The next stage will be the Alpha testnet, they will allow permissionless deployment of smart contracts, available to anyone.
Scroll’s mainnet will have a two-stage launch.
Phase 1 will run with a centralized sorter and a decentralized prover;
The main goal of the second phase is to decentralize the sorter.
While Phase 2 is still under active research, current plans will include PBS models for MEV extraction, on-chain Challenge mechanisms and a committee of orderers to allow for finalization before transactions are finalized on Ethereum L1.
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