Interview with Polygon zkEVM: Layer2 decentralized sorter is more important than the regulatory issues facing Ethereum

Interview: Jack, BlockBeats

Compilation: Laughing, BlockBeats

It seems that since EDCON in Montenegro, ZK has become a topic that everyone is talking about. But in fact, the popularity of the ZK track has not diminished since the Arbitrum airdrop at the beginning of the year. With the launch of zkSync Era, the expectation of "ZK Airdrop" has also been pushed to a new high point. In addition to zkSync and Starknet, zkEVM projects such as Scroll and Linea have also become the key targets of the "Wool Party".

But what's interesting is that despite the unprecedented high short-term expectations of the ZK track, most people still have a relatively vague concept of segmentation in this field. ZK Rollup, zkEVM, zk-SNARK, zk-STARK, etc., each one seems to be very important, but each one is not well understood. It must be admitted that the strong technicality of the ZK track has indeed added a lot of difficulty for many people to understand this field.

As the first team to invest in ZK expansion development, Polygon has experienced many iterations of its own products and has a deep understanding and insight into ZK Rollup. Polygon zkEVM is also one of the few zkEVMs that has been launched. To this end, BlockBeats recently interviewed Jordi Baylina, the technical director of Polygon zkEVM, and asked the "technical nerd" about the development status and opportunities of the ZK track, as well as the future prospects of Polygon zkEVM.

About ZK Rollup and zkEVM

**BlockBeats: First, can Jordi briefly explain to readers the difference between ZK Rollups and zkEVM? And why do we need a ZK-proven EVM? **

Jordi Baylina: From a user perspective, the biggest difference between OP Rollups and ZK Rollups is the time it takes to withdraw funds. For example, when you put 1 ETH into Optimism or Arbitrum, it takes at least a week to get the money back. If you want to keep your funds there, it's not that big of an issue. But when your funds are in multiple Rollup systems, the problem will be more complicated and the funds will be difficult to transfer. When you want to transfer funds to another Rollup, it takes a week or two. This is the biggest problem with OP Rollups.

In the case of ZK Rollup, you can exit the Rollup after generating a proof of verification. Currently, on Polygon zkEVM, this time is about an hour, but can be as short as 30 seconds. And 30 seconds and two weeks is a big difference. 30 seconds actually allows you to go to another rollup to trade, and then come back to the same rollup. So if you want your funds to be connected to the whole world, and you can transfer funds here, this has higher usability. I mean, it's important that you don't get stuck with funds that you can't move.

**BlockBeats: Compared with ZK Rollups such as Starknet and zkSync, what is the difference between Polygon zkEVM? **

Jordi Baylina: The biggest difference with Polygon zkEVM is that it is an EVM, which means it is fully compatible with Ethereum. Users can do the same things as on Ethereum just by connecting to MetaMask. You can deploy smart contracts, interact with smart contracts, create tokens, transfer money, create multi-signatures, whatever you want to do, you don’t need any special tools, you just use the same tools as on Ethereum, such as MetaMask, etherscan, HardHat, etc., all the tools available for Ethereum, you can use them, you don't need specific other tools.

**BlockBeats: The community often has the opinion that "ZK and EVM are not compatible". Why is there such a statement? **

**Jordi Baylina: **EVM was not originally designed with ZK proof in mind. The design of EVM was completed around 2014~2015, and the related concept of ZK proof appeared around 2018~2019. Therefore, ZK proof was not considered in the design of EVM. But in Polygon, we successfully built zkEVM through our own design, that is, built a proof system, a zkProver (zero-knowledge proof generator) that can verify any Ethereum transaction.

It can be verified in the same way as any Ethereum client, which means we have achieved full compatibility with Ethereum. So if you know how to develop on Ethereum, you should also know how to develop on zkEVM. You don't need anything else special. From the perspective of developers, they will hardly feel any difference, except for the difference in gas price and throughput.

**BlockBeats: Polygon itself is already an EVM-compatible sidechain, why does it need to build another Layer 2 expansion solution? **

Jordi Baylina: A Polygon has two parts. One is Polygon PoS, which is the original Polygon network, and the other is Polygon zkEVM. They are two separate networks that are not currently connected together. Polygon PoS is a Layer 1 sidechain, just like Gnosis, Avalanche or other Layer 1 sidechains. And Polygon zkEVM is a ZK Rollup and an EVM, which is compatible with Ethereum. In the end, you'll see it all come together and it's going to be extremely scalable.

In fact, this is what Polygon has been working on, so we created PoS so that it can become a better scaling Layer 1. But all Layer 1s have some limitations, namely the consensus mechanism. You can compromise security a little bit, but you can't get the security of Ethereum and so on at the same time. Polygon PoS is a tradeoff that can provide very fast and cheap transactions, it has some security compromises, but that doesn't mean it's insecure, just that it doesn't have the same level of security and decentralization as Ethereum . There are different balances in this "impossible triangle", and for many applications, this may be sufficient. But for a Layer 1, the consensus layer has always had limitations of one kind or another.

Real blockchain expansion needs to be realized through Layer 2 technology, so Polygon has invested a lot of money in building Layer 2 technology, specifically, ZK Rollup technology. Of course, we did Supernets in the Polygon PoS scaling attempt, but this is a way to develop in the Layer 1 ecosystem. For the overall scaling of the blockchain, Polygon is really very focused on ZK Rollups.

**BlockBeats: Many ZK Rollups employ zk-SNARKs, but Polygon zkEVM combines zk-SNARKs and zk-STARKs. And there have been a lot of discussions about the two recently. What do you think of zk-SNARK and STARK? **

Jordi Baylina: Currently STARK is the fastest proof system we know of. Also, another important factor is that it is very easy to implement full recursion on top of STARKs. This allows us to aggregate many blocks in a single transaction, which is very convenient. And we also use something different from StarWare, what we call a small prime field STARK, which is even 10 times faster than regular Stark.

Rhythm BlockBeats Note: In mathematics, a "small prime field" refers to a finite field characterized by a small prime number (also known as a finite prime field or a Galois field). In this field, all operations are performed modulo this prime number. Fields of small prime numbers are often used in fields such as cryptography and coding theory, because they have some important properties, such as good grouping effect and reversibility, etc.

**BlockBeats: In the field of ZK Rollup, everyone seems to be striving to achieve EVM compatibility or even equivalent, but Starknet, which is the leader, is not EVM compatible. **

Jordi Baylina: You can say that Starknet is Layer 2 of Ethereum because they are built on top of Ethereum. But in fact, one difference is whether it is compatible and equivalent to Ethereum, and Starknet is not compatible. It is equivalent if you connect MetaMask directly to this port and start using it. Or you can use Remix to create a smart contract and deploy it there, and it should behave exactly like Ethereum.

But Starknet uses a different language and compares to something different, like a different chain. You can't go to Remix (Ethereum development environment) and generate a smart contract and deploy it on Cairo, you need to use their own tools.

**BlockBeats: zkEVM projects like Kakarot choose to build a zkEVM on top of Starknet. What do you think of this technology implementation path? How is it technically different from Polygon zkEVM? **

Jordi Baylina: For the Kakarot team, they are trying to achieve compatibility with Ethereum, but in order to achieve this goal, the technology stack they adopted is a bit slow. Although the specific situation needs further observation, I think they may not be very efficient. The problem at the moment is that this project is very dependent on how zkEVM is built. And Kakarot is built on Cairo, Cairo is relatively slow, and the EVM is very complex, building on the basis of Cairo will be very inefficient. It's a two-tier tech stack, maybe it can work, but I think it's going to be small.

Instead of using a generic virtual machine like Cairo, we built a custom virtual machine. It's like building a specialized processor that executes a specific program. We customized the virtual machine instead of using the Cairo language. This virtual machine is specially designed to build zkEVM, just like designing a computer that can only run a single program.

**BlockBeats: So Polygon zkEVM will be developed using Solidity from the beginning? **

**Jordi Baylina:**Polygon is using the EVM, so it uses the same underlying technology as Ethereum. This means that you can develop in Solidity, and once you develop in Solidity, you can deploy not only on Ethereum, but also on zkEVM, because they use the same processor, the Ethereum Virtual Machine . While StarNet uses Cairo, it doesn't just use the EVM.

About OP Rollup and zkEVM track

**BlockBeats: One or two years ago, everyone thought that OP Rollups was the mainstream solution for short-term expansion. But now, several mainstream ZK Rollups have launched on the mainnet one after another. Do you think OP Rollups are still of great value to the expansion of Ethereum? **

Jordi Baylina: OP Rollups are a nice solution when ZK Rollups are not quite ready yet. But now that ZK Rollups are ready, I don't think there's much point in using OP Rollups anymore. Two years ago when zkEVM was still under construction, everyone thought it would take about five years of work, so OP Rollups might be a very reasonable choice in those five years. But after only two years, zkEVM has developed very well, and we reached that goal ahead of schedule.

Comparing OP Rollups, Starknet, and Polygon zkEVM, one of the major differences is that Polygon zkEVM is the only zkEVM that is actually implemented among the three, and the only zkEVM that is fully compatible with Ethereum. zkSync is compatible at the Solidity level, but you need to use specific tools to compile it, it is not EVM. Starnet is not compatible with Ethereum.

**BlockBeats: In your opinion, what key factors accelerated the development process of ZK Rollups? **

**Jordi Baylina: **The main thing is that when we put all the tools and technologies together, the combination of them plays a key role. It's an engineering process, like putting together many known parts. We have demonstrated to some extent that this is possible, and solved many challenges in the process.

For example, we initially needed hours in terms of proof time and the data centers needed to compute proofs. Now, building a proof takes only a minute on a large machine. So, you can see the progress in those two years. It's not a single factor, as I said before, for example, we went from the large prime field to the small prime field, we adopted STARKS, accelerated the hash function used in it, we learned how to do arithmetic and how to use Efficient way to implement keccak256 et al. in a circuit. We've created a really nice structure that enables different teams to work in parallel. We have the restriction layer, the cryptography layer, the ROM (read only memory) layer, which is actually implementing the testing layer. These different layers allow us to efficiently work in parallel, which is why we were able to build this system quickly.

**BlockBeats: But many voices from the community are still complaining that it takes a long time to transfer assets between Ethereum and Layer 2, or interact on Layer 2, and Gas fees are not much cheaper. why is that? **

Jordi Baylina: In terms of transferring assets between L1 and L2, this is not the case in Ethereum's zkEVM. From Layer 1 to Layer 2, two layers of processing are required. Therefore, you need to complete the transaction in Layer 1 to make it final, which takes about 12 minutes.

I don't think there's any other reason than that they didn't do it right. Currently, it takes 12 minutes to deposit funds at Polygon zkEVM, and we generate a proof every hour to withdraw funds, so the whole process should take no more than an hour and a half, even though this may fluctuate. That said, we know it will only take an hour at most, and it could be less.

The current gas fee is 10% of the Layer 1 gas fee because we need to pay for data availability. But what I can tell you is that in about six months, early next year, we plan to ramp up again, 50 times on top of the 10 times we have now. This 50x improvement comes primarily from data compression, an area we are currently working on. The other 10x comes from EIP-4844.

Rhythm BlockBeats Note: EIP-4844 (also known as the proto-danksharding proposal) was co-created by Vitalik Buterin and other programmers from the Ethereum ecosystem. The main purpose of EIP-4844 is to reduce gas costs on the network, especially for Rollup solutions, without sacrificing decentralization. Rollup solutions like Arbitrum and Optimism can reduce gas costs by a factor of 100 to 1000.

**BlockBeats: Currently, the zkEVM track is very competitive. polygon zkEVM, Consensys, and scroll are all vying for L2 users, and many users still can't tell the difference between them and Starknet and zkSync. In your opinion, what are the similarities and differences between Polygon zkEVM and other zkEVM projects? **

**Jordi Baylina: **Scroll has many similarities with us, Scroll is a zkEVM, and we are also zkEVM. And zkSync is not, it is a zkSolidity, and there is no EVM in the process of technical implementation. And Starknet isn't even an EVM, it's more of a sidechain. But that doesn't mean they are good or bad, they are different things.

zkEVM implements EVM, which means you can use zero-knowledge to prove EVM. This is fungible, which means you should be able to use it in exactly the same way as Ethereum. In the field of zkEVM, we are going to discuss Scroll, Consensys (Linea) and Polygon zkEVM, which can be said to be the three most advanced zkEVM projects at present, each of which has its own advantages and disadvantages. Of course there is also Taiko, but that is a Type 1 zkEVM.

Among them, Consensys pays more attention to the architectural design, so that end users do not feel the difference from EVM. Of course, their mainnet is not yet online, so we still need to wait until the mainnet is online to observe its actual performance. But from a user's point of view, there shouldn't be much of a difference.

Comparison of mainstream ZK Rollups and zkEVM technical architectures, source: Dewhales Research (Note: Polygon Hermez is the current Polygon zkEVM)

I think the Consensys architecture is very similar to the Polygon zkEVM, both are very state-focused, the difference between them is the cryptography part. I think the lattice-based approach they take is interesting, and we can look at how they do it, maybe that's an advantage. But from an architectural standpoint, we're very similar. And Scroll is a bit different, Scroll doesn't have as many hierarchies, it's more simplified and cohesive.

Rhythm BlockBeats Note: In cryptography, lattice-based cryptography is a branch of cryptography based on lattice theory, which uses the mathematical properties of lattice structures to build secure cryptosystems. A lattice is a set of linearly independent vectors in a multidimensional vector space. Lattice-based cryptography takes advantage of the intractability of lattice problems, the most famous of which are the Shortest Vector Problem (SVP for short) and the Closest Vector Problem (CVP for short). These problems are often intractable in high-dimensional spaces, requiring enormous computational resources and time even with modern computers. Compared with traditional cryptography based on number theory or elliptic curves, lattice-based cryptography has certain advantages in resisting quantum computing attacks. Since there is currently no known efficient quantum algorithm that can solve the lattice problem, lattice-based cryptography is regarded as a viable option to resist quantum computing attacks and has been widely studied and applied.

**BlockBeats: During your EDCON speech, you shared that the Polygon zkEVM team often communicates with “opponent teams” such as Scroll. What topics do you communicate with? How do you see the competitive relationship between each other? **

Jordi Baylina: We usually discuss very technical topics. Like, how does your project handle transactions, how to sequence, how to implement this particular code, how to solve this problem, how to solve that problem, we share a lot of insights on these topics.

In my opinion, we are not competing, to be precise, at least not on a technical level, but we are trying to avoid competition, which is what I talked about at the panel. We do not compete with anyone, but pursue a cooperative attitude. It's a very complex technique, and you're putting yourself on a higher level. I've learned a lot from other people and also imparted knowledge to other people, it's the way we move forward. Of course, there may be competition at the product level, marketing and tuning, but that's not a bad thing for users.

About ZK Acceleration

**BlockBeats: zkEVM also needs a sequencer right? **

Jordi Baylina: Currently zkEVM uses a centralized sorter. Like other sidechains, sidechains require a sorter, and the sorter can be centralized or decentralized. At present, most side chains use a centralized sorter, but at the same time they all plan to build a decentralized sorter. In Polygon there is a mechanism called "Proof of Efficiency", but currently it is a centralized sorter and we are working on a better solution.

**BlockBeats: In order to decentralize the sorter, will you launch a new Token? **

Jordi Baylina: We already have a Token, which is MATIC, and there is no need to launch a new Token. We already have a good, strong, valuable token. This token can be used for consensus layers, such as Polygon PoS, or for decentralized sorters, etc. It is very useful in many ways and will be a very important token for maintaining this infrastructure.

**BlockBeats: How long will it take for the sorter to be fully decentralized? **

Jordi Baylina: I'm not responsible for this part in Polygon, there are people from other teams in Polygon who are working on this problem. I hope it will happen as soon as possible, but I'm not sure, maybe six months or a year. It's not going to be a quick process, I don't think it will happen in the next month. But at least at Polygon there's an entire team working in that direction.

**BlockBeats: In addition, many people are researching the opportunity of "ZK mining". What do you think about this matter? **

Jordi Baylina: Currently, the proof generator is very centralized, but a decentralized proof generator will be implemented in the future. It is possible. It may take a while, but it will happen. To be precise, there are two things that need to be involved, one is sorting, and the other is verification. Both of these processes need to be decentralized, and the key is the sorter. Proof that a generator is just a machine that does computations, nothing more.

**BlockBeats: So there is an opportunity here? **

Jordi Baylina: Yes, absolutely. Although now is not the time, but there will be opportunities in the future.

**BlockBeats: Finally, how does Polygon as a whole see zkEVM? **

**Jordi Baylina: **ZK will be a core part. We have seen a Layer 2 ecosystem based on ZK, and many side chains can interact with each other. I'm not worried about proof generators, Ethereum governance, etc. I'm more worried about the sorter, we need a decentralized sorter.