Exclusive Interview with Polygon zkEVM: Decentralized Order Book on Layer2 More Important than Regulatory Issues Facing Ethereum

Exclusive interview with Polygon zkEVM: decentralized order book on Layer2 is more important than Ethereum's regulatory issues.

Interview: Jack, BlockBeats

Compiled by: Laughing, BlockBeats

It seems that since EDCON in Mount Black, ZK has become the topic of discussion for everyone. However, the heat of the ZK track has not diminished since the Arbitrum airdrop at the beginning of the year. With the launch of the zkSync Era, the expectation of “ZK airdrops” has been pushed to a new high. In addition to zkSync and Starknet, Scroll, Linea and other zkEVM projects have also become the focus of “wool party” attention.

But what’s interesting is that despite the unprecedented high expectations for the bearish expectations of the ZK track, most people still have a relatively vague understanding of the sub-concepts of this field. ZK Rollup, zkEVM, zk-SNARK, zk-STARK, etc., each seems to be important, but each one is not too 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.

Polygon, as the first team to invest in ZK expansion development, has undergone multiple iterations of its own products, has a deep understanding and insight into ZK Rollup, and Polygon zkEVM is also one of the few zkEVMs that have been launched. Therefore, BlockBeats recently interviewed Jordi Baylina, the technical lead of Polygon zkEVM, to ask about the current development status, opportunities, and future prospects of the ZK track.

About ZK Rollup and zkEVM

BlockBeats: First of all, Jordi, can you explain the difference between ZK Rollups and zkEVM to readers briefly? And why do we need an EVM that has been verified by ZK?

Jordi Baylina: From the user’s point of view, the biggest difference between OP Rollups and ZK Rollups is the time required to extract funds. For example, when you deposit 1 ETH into Optimism or Arbitrum, it will take at least a week to retrieve the money. If you want to leave the funds there, the problem is not that big. But when your funds are in multiple Rollup systems, the problem becomes more complex and the funds become difficult to transfer. When you want to transfer funds to another Rollup, it also takes a week or two. This is the biggest problem facing OP Rollups.

In the case of ZK Rollup, you can exit the Rollup after generating the verification proof. Currently, on Polygon zkEVM, this time is about an hour, but it can be as short as 30 seconds. And 30 seconds and two weeks are a big difference. 30 seconds actually allows you to trade on another Rollup and then return to the same Rollup. So if you want to connect your funds with the world and you can transfer funds here, there is higher availability. I mean, you won’t get stuck in the dilemma of funds that cannot be transferred, which is important.

BlockBeats: What are the differences between Polygon zkEVM and other ZK Rollups such as Starknet and zkSync?

Jordi Baylina: The biggest difference with Polygon zkEVM is that it is an EVM, which means that it is fully compatible with Ethereum. Users only need to connect MetaMask to do the same things as they would on Ethereum. You can deploy smart contracts, interact with smart contracts, create tokens, transfer them, create multisigs, and whatever you want to do, without any special tools. You only need to use the same tools as those used on Ethereum, such as MetaMask, etherscan, HardHat, and any other tool available on Ethereum. You don’t need any other specific tools.

BlockBeats: There is a common belief in the community that “ZK and EVM are incompatible.” Why is this the case?

Jordi Baylina: When the EVM was initially designed, it did not consider ZK proof. The EVM was designed around 2014-2015, while the concept of ZK proof emerged around 2018-2019, so ZK proof was not considered in the EVM design. However, in Polygon, we have successfully built zkEVM through our own design, which is 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 that we have achieved full compatibility with Ethereum. Therefore, 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 developer’s perspective, they will hardly feel any difference, except for the differences in gas prices and throughput.

BlockBeats: Polygon itself is already an EVM-compatible side chain. Why did it build another Layer 2 scaling solution?

Jordi Baylina: Polygon has two parts. One is Polygon PoS, which is the original Polygon network, and the other is Polygon zkEVM. They are two independent networks that are not currently connected. Polygon PoS is a Layer 1 sidechain, just like Gnosis, Avalanche, or other Layer 1 sidechains. Polygon zkEVM is a ZK Rollup and an EVM that is compatible with Ethereum. Finally, you will see them merge together, and it will be highly scalable.

Actually that’s exactly 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 consensus mechanisms. You can compromise a little on security, but you cannot have Ethereum-level security at the same time. Polygon PoS is a compromise that can provide very fast and cheap transactions. It makes some compromises on security, but that doesn’t mean it’s not secure, 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 enough. But for a Layer 1, there are always such or other limitations in the consensus layer.

Real blockchain scalability needs to be achieved through Layer 2 technologies, so Polygon has invested heavily in building Layer 2 technologies, specifically ZK Rollup technology. Of course, in Polygon PoS’s scaling attempts, we have done Supernets, but this is a way of developing in the Layer 1 ecosystem. For overall blockchain scalability, Polygon is really focused on ZK Rollups.

BlockBeats: Many ZK Rollups use zk-SNARK, but Polygon zkEVM combines zk-SNARK and zk-STARK. There have been many recent discussions about the two, how do you view zk-SNARK and STARK?

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

BlockBeats: In the ZK Rollup field, everyone seems to be striving for EVM compatibility or even equivalence, but as the leader, Starknet is not EVM compatible.

Jordi Baylina: You can say that Starknet is Ethereum’s Layer 2, because they are built on top of Ethereum. But in reality, one difference is whether it is compatible and equivalent to Ethereum, and Starknet is not compatible. If you connect MetaMask directly to this port and start using it, it is equivalent. Or you can use Remix to create a smart contract and deploy it in it, it should run exactly the same as Ethereum.

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

BlockBeats: Kakarot, a project that uses zkEVM, chooses to build another zkEVM on top of Starknet. What do you think of this technological implementation path? How is it different from the Polygon zkEVM at the technical level?

Jordi Baylina: For the Kakarot team, they tried to be compatible with Ethereum, but the technology stack they used to achieve this goal was somewhat slow. Although the specific situation still needs further observation, I think their efficiency may not be very high. The problem now is that this project is heavily dependent on the way zkEVM is built. And Kakarot is built on Cairo, which is relatively slow, and the EVM is very complex, so building on top of Cairo would be very inefficient. This is a two-layered technology stack, and maybe it can work, but I think the scale will be very small.

Instead of using a general-purpose virtual machine like Cairo, we built a custom virtual machine. Just like building a dedicated processor that executes a specific program. We customized the virtual machine rather than using the Cairo language. This virtual machine is specifically designed for building zkEVM, just like designing a computer that can only run a single program.

BlockBeats: So Polygon zkEVM will use Solidity for development from the beginning?

Jordi Baylina: Polygon uses EVM, so it uses the same underlying technology as Ethereum. This means that you can use Solidity for development, 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. StarkNet uses Cairo, which is not just using EVM.

About the OP Rollup and zkEVM tracks

BlockBeats: A year or two ago, everyone still thought that OP Rollups were the mainstream solution for scaling in the short term. But now, several mainstream ZK Rollups have been launched on the mainnet. Do you think OP Rollups still have important value for Ethereum scaling?

Jordi Baylina: OP Rollups were a good solution when ZK Rollups were not yet fully prepared. But now that ZK Rollups are ready, I think there is not much point in using OP Rollups. Two years ago when zkEVM was still under construction, everyone thought it would take about five years of work, so OP Rollups might have been a very reasonable choice during those five years. But after only two years, zkEVM has made good progress and we have achieved that goal ahead of schedule.

One major difference between OP Rollups, Starknet, and Polygon zkEVM is that Polygon zkEVM is the only truly implemented zkEVM among the three, and the only one fully compatible with Ethereum. zkSync is compatible at the Solidity layer, but you need to use specific tools to compile and it is not EVM. And Starnet is not Ethereum-compatible.

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

Jordi Baylina: The most important thing is the combined effect of all the tools and technologies when we put them together. This is an engineering process, like combining many known parts together. We have shown to some extent that it is possible, and we have solved many challenges in the process.

For example, we initially needed several hours for proof time and for the data center required to compute proofs. Now, building a proof on a large machine only takes one minute. So you can see the progress over these two years. This is not a single factor, as I said before, for example, we switched from large prime fields to small prime fields, we adopted STARKS, accelerated the hash functions used in it, we learned how to do arithmetic and how to efficiently implement keccak256 in circuits, etc. We created a very good architecture that allowed different teams to work in parallel. We have the constraint layer, the cryptographic layer, the ROM (read-only memory) layer, and this is actually being implemented in the test layer. These different layers allow us to work in parallel efficiently, which is why we can 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 to interact on Layer 2, and gas fees have not been reduced much. Why is this?

Jordi Baylina: Regarding transferring assets between L1 and L2, it is not as simple as in zkEVM on Ethereum. It requires two layers of processing to move from Layer 1 to Layer 2. Therefore, you need to complete the transaction in Layer 1 for it to be eventually confirmed, which takes about 12 minutes.

I think there is no other reason other than they did not execute the operation correctly. Currently, depositing funds in Polygon zkEVM takes 12 minutes, and we generate a proof every hour to extract the funds, so the entire process should not exceed an hour and a half, although this may fluctuate. That is to say, we know that it will take no more than an hour, and it may be even shorter.

The current Gas fee is 10% of the Layer 1 Gas fee, as 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, adding another 50 times on top of the current 10 times. The 50x increase mainly comes from data compression, which is an area we are currently working hard on. Another 10 times comes from EIP-4844.

BlockBeats: Currently, the competition in the zkEVM track is very fierce. Polygon zkEVM, Consensys, and Scroll are all competing for L2 users, while many users still cannot distinguish 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 a zkEVM. zkSync is not, it is a zkSolidity, and there is no EVM in the technical implementation process. And Starknet is not even an EVM, it is more like a sidechain. But that doesn’t mean they are good or bad, they are different things.

zkEVM implements the EVM, which means you can use zero-knowledge proofs with the EVM. This is interchangeable, which means you should be able to use it in exactly the same way as Ethereum. In the zkEVM field, we have to discuss Scroll, Consensys (Linea), and Polygon zkEVM, which can be said to be the three most advanced zkEVM projects currently, and we each have our own advantages and disadvantages. Of course, there is also Taiko, but that is a Type 1 zkEVM.

Among them, Consensys focuses more on architectural design to make end users feel no different from EVM. Of course, their mainnet has not yet gone live, so we still need to wait and see its actual performance after the mainnet goes live. But from the user’s perspective, there should not be too much difference.

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

I think Consensys architecture is very similar to Polygon zkEVM, both of which are very concerned about state, with the difference being in the cryptographic part. I think their use of lattice-based schemes is very interesting, and we can pay attention to their implementation method, perhaps this is an advantage. But from an architectural point of view, we are very similar. Scroll, on the other hand, is somewhat different, with fewer levels of hierarchy and more simplicity and coherence.

BlockBeats: You shared during your EDCON speech that the Polygon zkEVM team often communicates with “rival teams” such as Scroll. What are the main topics of discussion? How do you view the competitive relationship between each other?

Jordi Baylina: We usually discuss very technical topics. For example, how does your project handle transactions, how to sort them, how to implement this particular piece of 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 in competition, at least not at the technical level, and we are also trying to avoid competition, which is what I talked about at the roundtable. We are not competing with anyone, but pursuing a cooperative attitude. This is a very complex technology, and you have to put yourself at a higher level. I have learned a lot from others, and I also pass on knowledge to others, which is how we move forward. Of course, there may be competition in the product, marketing, and adjustment aspects, but this is not necessarily a bad thing for users.

About ZK Acceleration

BlockBeats: Does zkEVM also need a sorter?

Jordi Baylina: Currently, zkEVM uses a centralized sorter. Like other sidechains, sidechains require sorters, which can be centralized or decentralized. Currently, most sidechains use centralized sorters, but they also plan to build decentralized sorters. In Polygon, there is a mechanism called “Proof of Efficiency”, but currently it is a centralized sorter, and we are working hard to find a better solution.

BlockBeats: Will you launch a new Token to make the sorter go decentralized?

Jordi Baylina: We already have a Token, which is MATIC. We don’t need to launch a new Token. We already have a great, powerful, and valuable token. This token can be used in the consensus layer, such as Polygon PoS, and can also be used in decentralized sorters and so on. It is very useful in many ways and will be a very important Token for maintaining this infrastructure.

BlockBeats: How long does it take for the sorter to go completely decentralized?

Jordi Baylina: I am not responsible for this part in Polygon. There are other teams in Polygon dealing with this issue. I hope it can be achieved as soon as possible, but I’m not sure. It may take six months or a year. This will not be a fast process, and I don’t think it can be achieved next month. But at least there is a complete team in Polygon dedicated to moving in this direction.

BlockBeats: In addition, many people are researching the opportunity of “ZK Mining”. What do you think of this?

Jordi Baylina: Currently, the proof generator is very centralized, but a decentralized proof generator will be implemented in the future. This is possible. It may take some time, but it will happen. Specifically, there are two things that need to be involved, one is sorting, and the other is verification, both of which need to be decentralized, with the key being the sorter. The proof generator is just a machine for doing calculations.

BlockBeats: So there is an opportunity here?

Jordi Baylina: Yes, absolutely. Although it’s not the time yet, there will be opportunities in the future.

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

Jordi Baylina: ZK will be a core part. We see a Layer 2 ecosystem based on ZK, and many side chains can interact with each other. I’m not worried about the proof generator and Ethereum supervision. I’m more concerned about the sorter, and we need a decentralized sorter.

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