A summary of the encryption project trying Hybrid Rollup

Author: 0x Facai, Jaleel, BlockBeats

On June 16, Frax Finance, a mixed-algorithm stablecoin protocol, announced the launch of an Ethereum Layer 2 network called Fraxchain, and all Frax assets will be natively supported on Fraxchain. It is reported that Fraxchain will adopt a Hybrid rollup expansion scheme that mixes OP Rollups and ZK Rollups, aiming to achieve better scalability, faster finalization and enhanced security against competitors, which has caused a lot of excitement in the encryption community. focus on.

In fact, this fusion of Rollup ideas is nothing new. As early as July 2022, Optimism core developer Kelvin Fichter developed the Optimism Bedrock architecture. Similar products have advantages, and Bedrock aims to make a seamless transition between Optimistic and ZK possible", and based on this topic, I discussed with Ethereum co-founder Vitalik Buterin.

Following Kelvin Fichter's idea, Vitalik Buterin, the co-founder of Ethereum, also expressed his opinion: Combining Optimistic Rollups and ZK Rollups, governance is only used to solve the bugs between the two. The process is: 1) Release area block, 2) wait for a 24-hour fraudulent challenge period; 3 (a) if there is no challenge, issue a ZK SNARK for final confirmation; 3 (b) if there is a challenge, according to the 3 Decide on 2 of the options.

As more and more people join the competition for Layer 2 expansion, this kind of Rollup fusion expansion idea is being applied more and more. In addition to Optimism, there are many teams on the market that have begun to research and try Hybrid Rollups. What are Hybrid Rollups? Why choose Hybrid Rollups? What teams are doing development in this area? BlockBeats parsed and organized it in this article.

What is Hybrid Rollup?

**Hybrid Rollup is a kind of Rollup with mixed thinking. By combining Optimistic Rollups and ZK Rollup two technologies, the product function is optimized to the greatest extent, so as to find the best fit point PMF (Product-Market Fit) between the product and the market, that is Achieve product-market fit. **

To figure out what a Hybrid Rollup is, you first need to understand what Optimistic Rollup and ZK Rollup are.

First of all, Rollup is one of the expansion schemes of Ethereum. It transfers the calculation and storage of transactions on the Ethereum mainnet (Layer 1) to Layer 2 for processing and compression, and then uploads the compressed data to the Ethereum mainnet for expansion. Ethereum performance.

Essentially, instead of sending transactions to L1 miners, users send their transactions to Rollup servers, which execute transactions outside of the Ethereum main chain. However, these Rollups publish transaction data to the Ethereum main chain. When transactions are published to the main chain, they will inherit the security properties of L1. Rollup is usually programmable, so it needs to support the smart contract (SC) language so that developers can develop DApps. However, since Privacy is not compatible with EVM (Ethereum Virtual Machine), Solidity cannot be directly used to develop privacy-type DApps. This requires a customized smart contract language to support both public and private contract writing. Of course, this requires VM module adaptation due to the need to maintain different types of state trees.

Rollups typically operate at the second layer, with the flexibility to operate at the third layer.

According to different schemes to ensure the validity of the compressed data (that is, the data is correct), Rollup can be divided into ZK Rollup and Optimistic Rollup.

ZK Rollup is a rollup scheme using zero-knowledge proof, and ZK is the abbreviation of zero knowledge. The difference from other Rollups is that ZK Rollup uses the zkSNARK algorithm (a zero-knowledge proof algorithm) to compress data and ensure security.

Optimistic Rollup is literally understood as an optimistic Rollup. It optimistically defaults that the data synchronized to Layer 1 is correct. If anyone thinks that the synchronized data is incorrect (that is, there is fraud), they can issue a challenge during the challenge period. Therefore, this proof method is also called fraudulent proof, so as to ensure that the data that is finally synchronized to Layer 1 is valid.

Hybrid is a solution that mixes two types of Rollup, and supports more contract types, including public, private and hybrid contract types. For developers, they can freely choose contract types based on their own needs. For users, it also has more advantages. High degree of freedom, you can freely choose the transaction type in the mixed contract.

The diagram below briefly depicts the positioning and function of the Hybrid Rollup. Currently, several projects are known to work on building in this direction. Although the technical details of each project are different, they all share a common vision: to bring more possibilities, higher security performance, more real-world scenarios and more daily life to the blockchain industry. user.

Which teams are trying Hybrid Rollup?

OP+ZK's Rollup technology sounds far away from us, but in fact, many well-known encryption protocols and projects have tried in this field. In addition to Frax Finance, which recently announced the L2 network Fraxchain, there are many first-class teams that have also made their own products. BlockBeats briefly sorted out these protocols and projects.

Frax Finance

BlockBeats previously reported that, according to The Block, on June 16, Frax Finance, a hybrid algorithm stablecoin protocol, announced that it would launch an Ethereum Layer 2 network called Fraxchain, which will be dedicated to creating a smart contract platform with a focus on decentralization. In the financial field, all Frax assets will be natively supported on Fraxchain. Frax Finance co-founder Sam Kazemian revealed that Fraxchain is likely to launch by the end of this year.

In addition, Sam Kazemian, founder of Frax Finance, recently participated in the podcast program "Flywheel DeFi" and revealed that unlike most second-tier expansion solutions on the market, Fraxchain will adopt a Hybrid rollup expansion solution that mixes OP Rollups and ZK Rollups, which means Fraxchain will be built on an Optimistic rollup architecture with integrated zero-knowledge proofs designed to achieve better scalability, faster finality and enhanced security against competitors.

Notably, the network will use the Frax stablecoin and Frax Ether (Frax liquid collateralized derivatives) to pay for transaction fees. A portion of fees generated in this layer-2 network will be burned or redirected back to the Ethereum mainnet for distribution to holders of FXS governance tokens.

Placed

BlockBeats previously reported that on March 3 this year, MetisDAO, which focuses on L2 construction, said in a blog post that Metis, the Ethereum Layer 2 network, is developing a hybrid Rollup based on the combination of Optimistic Rollup (OPR) and Zero Knowledge Proof (ZKP). The scalability of ZK Rollup combined with the security of ZK Rollup. At the same time, Metis said it will develop this new architecture as one of its top priorities and will open source the technology.

In the 2023 roadmap released by Metis Andromeda, Hybrid Rollup occupies a large space, which is enough to prove the importance that Metis attaches to it.

Workflow of Hybrid Rollup in Metis Network Aztec

BlockBeats previously reported that on May 4, Aztec announced that it will launch a public and private hybrid zkRollup network, which will continue to use the name of Aztec, which is characterized by the ability to execute public and private smart contracts in an environment, which will Helps expand developers' design choices on the chain.

Aztec allows the execution of smart contract logic in a public and private manner, while still inheriting the security advantages of Ethereum. On Aztec, privacy is optional, not required by default. Its goal is to extend Ethereum with features such as private function calls, transaction privacy, and user anonymity while all data remains public. This allows users to protect sensitive information from disclosure while still being able to share it with relevant agencies for compliance purposes when necessary. Aztec also stated that the team is currently completing basic contract deployment and expects to establish a local testnet by the third quarter of 2023, while users are expected to have access to a mature public testnet by early 2024.

Polygon

In May last year, Polygon established a partnership with global professional services and technology company Ernest & Young (EY, Ernest & Young) and released Nightfall 3.0. Polygon Nightfall is essentially an Optimistic Rollup that uses zk encryption to protect privacy. The most prominent feature is that it effectively combines the backbone concept of Optimistic Rollup with the zero-knowledge (ZK) cryptography commonly used in ZK-Rollups to achieve scalability. The fusion of sex and privacy.

In fact, as early as 2019, Ernst & Young announced the initial version of Nightfall. The most different point from other zk solutions is that Nightfall is a privacy-focused rollup. One of the solutions". Specifically, every transaction on Nightfall includes privacy, meaning that if Alice sends an asset to Bob, no one else can see what that asset is, how much value it contains, or where it went.

The reason why it pays more attention to the privacy of transactions is that the customers targeted by Ernst & Young are enterprises. At the beginning, Nightfall tried to build the first enterprise-level blockchain directly on Ethereum, but finally found that having privacy on the Ethereum mainnet was too expensive, so they switched to L2 and finally chose to cooperate with Polygon.

Mine

O( 1) Labs, the development team of Mina, a lightweight blockchain protocol, has submitted a proposal to Optimism (renamed OP Mainnet), suggesting that its zero-knowledge proof technology based on MIPS zkVM be applied to OP Stack fraud proofs, in which MIPS features Allows writing applications in a common language in addition to native high-performance snarkyJS.

In addition, Optimism has completed the upgrade of the main network Bedrock at 2:50 a.m. Beijing time on June 7. After the upgrade, it can not only reduce transaction costs, shorten system delays, and improve node performance, but also upgrade. In addition, it also makes the seamless connection between Optimistic and ZK possible.

Why choose Hybrid Rollups?

Using the hybrid architecture of "Optimistic + ZK Rollups" can maximize the advantages of both, which means that not only can the Optimistic Rollup architecture be retained, EVM is compatible, but also the universal zero-knowledge proof can maximize security, Its validity proof can clearly ensure the correctness of off-chain transactions, and at the same time, prevent operators from performing invalid state transitions.

ZK Rollup improves throughput because zero-knowledge proofs eliminate the need for additional data, keeping only the bare minimum required for each transaction. This greatly increases throughput and reduces Ethereum congestion.

In addition, ZK Rollup brings additional benefits of increased transaction speed and faster finalization.

By implementing zero-knowledge proofs to the Optimistic Rollup architecture, transaction finalization time will be reduced from 7 days to approximately 4 hours. There are generally two types of time, confirmation time and finalization time. Optimistic Rollup provides faster confirmation time. However, the premise of Optimistic Rollup is that all transactions are valid at the beginning, so a buffer period of 7 days is required, that is, the transaction needs to be confirmed for 7 days before the full transaction can be realized. Sure, the 7-day window is for validators to submit fraud proofs (if requested). Combined with zero-knowledge proofs, it is faster to confirm the validity of a transaction as long as the prover generates the proof and the verifier approves it.

Funds can be withdrawn from L2 without delay, which also means that converged Rollup will bring users higher capital efficiency.