Understanding Rollup in One Article: The Differences Between ZK Rollups, Optimistic, and Arbitrum
What are the differences between rollups?*Original Title: 《 Easily Understand the Differences Between Rollup, ZK Rollups, and Optimistic, Arbitrum */
Author: Future Xiao Ge
01 What is Rollup
As the name suggests, Rollup means to summarize and organize.
In the Ethereum network, due to the bandwidth limitations of the ETH network, gas fees often increase significantly during periods of high transaction congestion. This makes the cost of a single transaction very high, sometimes reaching hundreds of dollars, and the speed is very slow.
This is similar to the difference in waiting times and prices when dining on weekdays versus during holiday travel in tourist areas (a bread that costs 5 yuan on a regular day might sell for 50 yuan during peak tourist season); or the difference between toll booths on highways during weekdays and holidays.
Every transaction on Ethereum contains data, and each piece of data consumes gas. Since the Ethereum network has set limits on the amount of data per block and the TPS (transactions per second), how can we increase Ethereum's capacity and speed, TPS, without moving all data off-chain? Rollup comes into play.
The role of Rollup is to copy the content that needs to be computed on Ethereum and send it to a Layer 2 protocol connected outside of Ethereum for computation. Then, the result information is compressed, packaged, and sent back to the on-chain network.
The compressed block contains a large amount of signature confirmation information. Originally, each transaction on-chain could only have one confirmation signature per block, but now this block is equivalent to a VIP signature block that compresses many transaction signatures. One VIP signature passing is equivalent to 100 signatures passing. This indirectly significantly increases Ethereum's TPS.
This is similar to everyone having one question, but stating them one by one in a meeting is time-consuming and labor-intensive. By electing trusted representatives to summarize and review everyone's questions, efficiency is greatly improved. When one representative answers their question, it is equivalent to 100 questions being resolved.
The part of the data on-chain remains unchanged, so the reliability of the representative (Rollup Layer 2 protocol) also determines the security of Ethereum. Different Rollup models produce different styles and advantages.
So, here is a quick explanation of a few representatives, the shallow differences between ZK Rollups and Optimistic:
02 What are ZK Rollups
ZK Rollups, ZKSnark, or Zero Knowledge Rollups, as the name suggests, use zero-knowledge proofs to verify the Rollup process. Zero-knowledge proofs are one of the main contributions of Silvio Micali, the founder of the blockchain public project Algorand, in cryptography.
The four main characteristics of ZK (note that it is ZK, not JK):
- Zero Knowledge: The verifier does not need to see the data on the transaction platform.
- Succinct: Concise and succinct.
- Non-Interactive: No need to know who the verifier is.
- Argument of Knowledge: Proving the authenticity and correctness of the transaction.
Therefore, the core method of ZK Rollups is to use rigorous and complex verification algorithms, where verifiers (ZkSnarker/Validator) in the Layer 2 protocol authenticate the validity of different data (Validity Proof), thus packaging the authentication results. After excluding redundant work information, the Ethereum network can directly absorb data blocks containing a large amount of compressed signature information.
Anyone can participate in network authentication and become an authenticator, so essentially, ZKSnark is also a Layer 2 protocol based on a PoW consensus mechanism.
Advantages:
- Layer 2 is verified by Ethereum quickly, allowing assets on Layer 2 to be withdrawn back to Layer 1 Ethereum swiftly.
- Very suitable for applications in payments, banking, trading platforms, and other businesses that require rapid settlement.
Disadvantages: Due to the complexity of the algorithm, there is a bit of a barrier to application development.
However, if a more Dapp-friendly model can be developed based on the algorithm in the future, ZK still holds the most long-term scalability value.
03 What are Optimistic Rollups Layer 2
The Optimistic approach, as its name suggests, is optimistic, initially assuming that all sent transactions are trustworthy and verified.
Layer 2 verifiers need to stake tokens as collateral. If during the verification process, someone discovers an issue with the packaging, that verifier (Sequencer) will be fined a portion of their tokens, which will be rewarded to the person who identified the issue.
After each data packaging, there will be a verification period for other verifiers to check for issues and determine if the packaging needs to be reverted.
Optimistic Rollups also have smart contract functionality and can have corresponding governance tokens.
The essential difference between Op Rollups and ZK Rollups is that in ZK, anyone can participate in the authentication through PoW, while OP tends to select a group of trusted authenticators to supervise the entire transaction packaging process.
Advantages:
- Suitable for developing Dapps, allowing for almost seamless migration of projects originally on Layer 1, while also developing the corresponding OVM virtual machine.
Disadvantages:
- The speed of withdrawing from Layer 2 to Layer 1 is relatively slow, usually taking over a week (because it requires verifiers to validate the authenticity of the packaging), but there are currently optimization protocols being developed to help speed up this process.
- There is a risk cost of malicious behavior by verifiers.
The OP Token we often discuss is one of the Layer 2 protocols that utilize the Optimistic method, while Arbitrum is also a Layer 2 protocol developed using the Optimistic Rollups model. Since the names of the Optimism project and the Optimistic Rollup method are very similar, it is easy to confuse them.
04 What is Arbitrum
First, as mentioned earlier, Arbitrum is essentially a Layer 2 protocol project that utilizes the optimistic Optimistic Rollup model. It is often compared with the Optimism project and currently has the highest TVL among many protocols at the Layer 2 level. The OP project only conducts one round of fraud proofs during authentication, and the transaction calculations on Layer 2 rely on Layer 1 for execution.
In contrast, Arbitrum conducts multiple rounds of fraud proofs during verification. Additionally, Arbitrum's transactions are not executed on Layer 1 and have their own virtual machine, making it more compatible with the ETH network.
Summary:
This article attempts to explain several hot concepts that confuse many friends around me using simple examples, including the author who has also been troubled by various OP, ZK series projects and methodologies. After reflection and explanation through examples, I hope to provide everyone with a clearer concept. For those interested in the technical aspects, you can consult engineers developing the corresponding protocols. To preserve some brain cells, this article will not delve into technical details. Finally, let's summarize:
Rollup refers to a method of organizing, sending a batch of transaction tasks to Layer 2 protocols to enhance Ethereum's operational efficiency.
ZK Rollups refer to a Layer 2 method that utilizes zero-knowledge proof cryptographic algorithms to complete outsourced work without needing to know who the verifier is.
Optimistic Rollups refer to a Layer 2 method that utilizes a group of verifiers, assuming the packaging is good by default, to supervise and discover bugs through a reward and punishment mechanism.
Both Optimism and Arbitrum are projects developed based on the Optimistic Rollups method.
Zksync, ZKxxxxxxx, and many ZK projects are developed based on or as a gimmick of the ZK Rollups method.
Currently, ZK Rollups are more suitable for payments and other businesses requiring rapid transactions, with slightly complex algorithms; while Optimistic methods are more suitable for Dapp development and DeFi businesses, although the withdrawal time is a bit long.
Other Layer 2 protocols, such as Plasma, Metis, and Truebit, which utilize game theory and AI, are also exploring optimal solutions for Ethereum's scalability.
Note: This article is for educational purposes only and does not constitute investment advice. Please make rational judgments. If you reprint the article, please indicate the author's source. If reposting on Twitter, please @santili1021.
