Popular science | why Rollup can become the hottest Layer 2 solution


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Unless you hide in the deep mountains and old forests, it is hard not to know this wave of enthusiasm caused by the two-layer scalable solution Rollup of Ethereum.

In September 2020, the gas price of Ethereum broke a record high, exceeding 477 Gwei. Perhaps this indicates that the day when the gas price rises to Twei is not far away.

Since the ICO boom in 2017, the Ethereum network has not been so congested. It can be said that the level of congestion is higher now. The block gas limit also hit a record high of 12.5 million. Transaction volume reached the peak level in 2017, and the block size also reached the highest level in history.

科普 | Rollup为何能成为当下最火的Layer2方案 Although this is encouraging news for improving the usefulness of the Ethereum network (at least from these indicators), one might argue that the current low-level scalability issues greatly limit applications and Seriously affect the user experience. However, this problem is not new anymore. The Ethereum community foresaw this problem several years ago and has been exploring solutions ever since.

Currently, research is mainly focused on the underlying PoS and fragmentation mechanism. In the next few months, we will soon see phase 0 go live. However, the computational scalability of Eth2.0 (that is, state execution through smart contracts in shards) will not be realized until phase 2, and it is currently expected to wait until after 2021.

In computer science, all problems can be solved in another roundabout way. ——

The roundabout approach adopted by the Layer 2 solution is to process transactions on Layer 2 and only use Layer 1 when necessary. Such solutions include state channels, side chains, and Plasma. Over the years, many projects have explored these solutions and made great progress.

Recently, the USDT issued by Bitfinex’s sister company, Tether, is the stable currency with the highest market capitalization and has always been a consumer of Ethereum gas. Tether has the More Viable Plasma Layer 2 solution.

Reddit organized the “Super Reddit Scalability Program ()” contest to improve the scalability of its Ethereum-based Community Points program (currently only implemented in two sub-reddit sections). Currently, the competition has received 22 proposals for Layer 2 solutions.

However, one thing to note is that Layer 1 and Layer 2 solutions are not mutually exclusive, but multiply.

科普 | Rollup为何能成为当下最火的Layer2方案 Therefore, although Eth 2.0 will be launched in stages over the next few years, the Layer 2 solution is expected to provide much-needed scalability before and after.

科普 | Rollup为何能成为当下最火的Layer2方案 In the past few years, the research on the Layer 2 solution has mainly focused on the state channel and the Plasma project, but the Rollup solution has been very popular recently and has made great progress.

Therefore, this article will explore Rollup in depth, and summarize it from the reasons, definition, and adoption. We will introduce the concepts of two types of Rollup solutions-ZK Rollups and Optimistic Rollups-and some major implementations. Finally, we will also mention various initiatives on the Status Network that may benefit from the Layer 2 solution, as well as our upcoming projects.

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Why use Rollups?

Background knowledge : The scalability solution built on Ethereum without any modification to the underlying Layer 1 protocol is called the Layer 2 solution. These solutions can process transactions without interacting with the Ethereum network, and anchor their security to Layer 1 of Ethereum through smart contracts.

The Layer 2 solution is attractive because multiple similar solutions can be run on Ethereum, only for those applications that can perceive Layer 2, without requiring everyone to upgrade the underlying infrastructure (this is a very risky and large engineering). Although Layer 2 does not necessarily provide the same security and certainty as Layer 1, it can increase throughput, reduce costs, and improve user experience compared to Layer 1. For some applications, Layer 2 is sufficient.

Currently, the most promising Layer 2 solutions are state channels and Plasma.

The status channel is most suitable for applications where the number of participants is determined and the status updates need to be exchanged multiple times within a period of time; in addition, it also requires strong availability guarantees to meet the security needs of the “challenge period”. It is a typical example of using state channels to help dApp achieve scalability.

Plasma was created by Vitalik Buterin and Joseph Poon in August 2017. Plasma is a scalability. Assets can be transferred into/out of the sub-chain through smart contracts on the root chain. All transaction executions occur on the sub-chain. The state promise (through the Merck created based on all state updates in the block) Ergen) will be published on the root chain, and can be used in fraud proofs when it exits the root chain later. Plasma has multiple variants, including Minimum Viable Plasma, More Viable Plasma, Cash, Debit and Prime. More Viable Plasma of OMG Network is a recent Plasma project that has been adopted by the market.

Disadvantages : The biggest disadvantage of the state channel is its liveness assumption. Users or their delegates need to monitor Layer 1 all the time to deal with various challenges. Plasma not only inherits this liveness hypothesis, but also introduces the data availability hypothesis, that is, users need to trust the operator to provide all transaction data in order to use the data to verify the correctness of the transaction when needed. Without data availability, in the worst case, large-scale problems may arise when users exit the Plasma chain. Neither state channels nor Plasma support smart contracts, which severely limits applications that require EVM compatibility.

科普 | Rollup为何能成为当下最火的Layer2方案 Looking at (), Rollup does not need to introduce the above two restrictive assumptions. These two assumptions will cause inconvenience in many cases. For most applications, Rollup is more promising than state channels and Plasma.

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Next, let us introduce the definition of Rollup and why it does not need to introduce restrictive assumptions like state channels and Plasma.

What is Rollup?

Rollup is very similar to Plasma. There is only one major difference, which avoids the data availability assumption, that is, all Layer 2 transactions will be “aggregated” into the call data of one transaction (call data is the storage data parameter of the Ethereum transaction) Read-only area), then package it into a block and submit it to Layer 1.

In view of the fact that the cost of calling data is much lower than that of Layer 1 storage (contract storage), the Rollup solution allows anyone to obtain transaction data on Layer 2 from Layer 1 at any time (unlike the Plasma solution, which is just Merkel root). ), used to verify the state transition. Therefore, once Layer 2 data is submitted, it can be obtained from Layer 1. This feature can eliminate the requirements of liveness assumptions and data availability assumptions, giving Rollup more advantages than state channels and Plasma.

According to the verification method of state transition, we can divide Rollup into two categories: ZK Rollup and Optimistic Rollup.

ZK Rollup (ZKR) : In ZKR, the operator must generate a validity certificate for each state transition on Layer 2 and submit these validity certificates to the Rollup contract on Layer 1. The Rollup contract verifies whether these proofs of state transition from the old Merkel root to the new Merkel root are valid. Although new components are used, these guarantees are cryptographic in nature.

Optimistic Rollup (OR) : In OR, the operator submits the new Merkel root together with transaction data to the Rollup contract on Layer 1. Everyone will assume that this is a valid state transition (it will not be verified as in the ZKR scheme) and move forward optimistically. Because, if the status proof is invalid, some participants will use the fraud proof to challenge it. These guarantees are cryptographically economic in nature, because token rewards and staking and forfeiture mechanisms will incentivize operators to remain honest.

According to the comparative analysis (), ZKR is more suitable for token transfers with a shorter finalization time (about 1-20 minutes), but it does not support EVM-compatible smart contracts required for general-purpose applications. In contrast, OR is more suitable for applications that require EVM-compatible smart contracts, but by default, the finalization time is longer (about 1 to 2 weeks) because it needs to wait for the end of the fraud proof challenge period. (However, there are some technologies that can provide financial guarantees to shorten the OR finalization time and withdrawal time.)

Who is developing Rollup?

Many teams are developing ZKR and OR implementations, and have designed different assumptions and features according to different scenarios.

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ZKR : Developed by the Matter Labs team has been launched on the Ethereum mainnet . Loopring has used ZKR for centralized exchanges and payment services. The StarkWare team is a ZKR technology that uses (not zk-SNARK), so it does not rely on trusted settings, has greater scalability, and can resist quantum computing attacks.

OR : At least 9 projects are studying different OR variants (for details, please refer to the comparison table in). The biggest difference is whether to support the interactivity requirements of EVM compatibility and fraud proof challenges. For example,, and support EVM-compatible smart contracts and non-interactive fraud proofs.

科普 | Rollup为何能成为当下最火的Layer2方案

Status Network

A big vision of Status is to become a “window on Ethereum”. Although it does not directly interact with the Ethereum blockchain, the application integrates a secure cryptographic wallet and Web3.0 browser. Both of these need to interact with Ethereum, due to the scalability challenges mentioned above, they will be directly affected by the soaring gas price.

Its products are exploring the construction of a payment network designed to meet the credit card-level scalability and instant certainty that the current Ethereum network does not have.

In addition, Status Network has also taken many other initiatives, such as,, and. These measures require lower gas prices to achieve viable deployment and a good user experience.

Although the Status Network team is cooperating with other client teams to develop Ethereum 2.0, the aforementioned Status initiative will soon benefit from the Layer 2 scalability solution.

Therefore, our Status team has been evaluating the Layer 2 solution for some time. For all the reasons mentioned above, Rollup is definitely the first choice. Among them, the Optimistic Rollup solution that supports smart contracts is more attractive to us because it is suitable for all our use cases.

Peer-to-peer : Currently, all Rollup architectures rely on operators to aggregate all transactions from clients and use traditional client-server architecture to create blocks. The disadvantage is that it may introduce centralization and censorship and reduce privacy.

Therefore, our Status team is exploring how client-operator interactions on Layer 2 can use our decentralized point-to-point protocol (eg) to provide privacy-protected routing and censorship resistance. For example, using Waku to route transactions to different operators not only protects the privacy of customers, but also provides them with different paths to publish transactions while resisting censorship.

in conclusion

Although we plan to upgrade to Ethereum 2.0 on a large scale in the next few years, the Layer 2 solution has continued to evolve over the past few years, and Rollup has become a rookie after State Channel and Plasma.

In this article, we comprehensively investigated the Layer 2 environment and summarized different solutions and their advantages and disadvantages to encourage more projects to adopt Rollup. Finally, we also mentioned the exploration of the Layer 2 solution by the Status team.