Exclusive Interview with Polygon zkEVM: One MATIC Token is Enough

Interview: Jack, BlockBeats

Compilation: Laughing, BlockBeats

It seems that since the Montenegro EDCON, ZK has become a topic that everyone is discussing. But in fact, the popularity of the ZK track has never 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. In addition to zkSync and Starknet, zkEVM projects such as Scroll and Linea have also become the focus of "wool party".

But what's interesting is that although the short expectations of the ZK track are unprecedentedly high, most people still have a relatively vague concept of the subdivision of 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 earliest team to invest in ZK expansion development, Polygon has undergone multiple 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 have been launched. For this reason, BlockBeats recently interviewed Jordi Baylina, the technical director of Polygon zkEVM, and asked this "tech geek" 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 of all, can Jordi briefly explain to readers the difference between ZK Rollups and zkEVM? And why do we need a ZK-verified EVM?

Jordi Baylina:From a user's 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 the funds there, the problem is not that big. But when your funds are in multiple Rollup systems, the problem becomes more complicated 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 a ZK Rollup, you can exit the Rollup after you generate the verification proof. Right now, on Polygon zkEVM, that time is about an hour, but it can be as short as 30 seconds. And 30 seconds is a big difference from two weeks. 30 seconds actually allows you to go to another Rollup, make a transaction, and then come back to the same Rollup. So if you want your funds to be connected to the world and you can move funds here, this has higher availability. I mean, you won't be stuck with funds that can't be moved, which is important.

BlockBeats: What is the difference between Polygon zkEVM and ZK Rollups like Starknet and zkSync?

Jordi Baylina: The biggest difference with Polygon zkEVM is that it is an EVM, which means it is fully compatible with Ethereum. Users just connect MetaMask and can do the same things as on Ethereum. 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 that can be used for Ethereum, you can use them, you don't need specific other tools.

BlockBeats: The community often has the view that "ZK and EVM are incompatible". Why is there such a saying?

Jordi Baylina:EVM was not originally designed with ZK proof in mind. The design of EVM was completed around 2014-2015, and the related ZK proof concept appeared around 2018-2019, so ZK proof was not considered when EVM was designed. But at Polygon, we have successfully built zkEVM by our own design, that is, we have 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 that we have achieved full compatibility with Ethereum. So if you know how to develop on Ethereum, then 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 difference in gas prices and throughput.

BlockBeats: Polygon itself is already an EVM-compatible sidechain, why is it building 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 together. Polygon PoS is a Layer 1 sidechain, just like Gnosis, Avalanche or other Layer 1 sidechains. And Polygon zkEVM is a ZK Rollup, which is also an EVM, and it is compatible with Ethereum. In the end, you will see them merged together, and it will be extremely scalable.

In fact, this is exactly what Polygon has been working on, so we created PoS so that it can be a better scaling Layer 1. But all Layer 1s have some limitations, namely the consensus mechanism. You can compromise slightly on security, but you can't get the security of Ethereum and so on. Polygon PoS is a trade-off that can provide very fast and cheap transactions. It has some compromises in security, but that doesn't mean it's not secure, it just 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, the consensus layer has always been limited in one way or another.

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

BlockBeats: Many ZK Rollups use zk-SNARK, but Polygon zkEVM combines zk-SNARK and zk-STARK. There has been a lot of discussion 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. 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, which we call a small prime field STARK, which is even 10 times faster than ordinary Stark.

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

BlockBeats: In the ZK Rollup space, everyone seems to be striving for EVM compatibility or even equivalence, but Starknet, as the leader, is non-EVM compatible.

Jordi Baylina: You can say Starknet is Ethereum's Layer 2 because they are built on Ethereum. But in fact, 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 create a smart contract with Remix and deploy it there, and it should run exactly the same as Ethereum.

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

BlockBeats: zkEVM projects like Kakarot choose to build another zkEVM on Starknet. What do you think of this technical implementation path? How is it different from Polygon zkEVM at the technical level?

Jordi Baylina：For the Kakarot team, they are trying to achieve compatibility with Ethereum, but they are using a technology stack that is a bit slow to get there. Although it remains to be seen, I think they may not be very efficient. The problem is that the project is very dependent on the way zkEVM is built. And Kakarot is built on Cairo, which is relatively slow, and the EVM is very complex, and building on top of Cairo will be very inefficient. It's a two-layer technology stack, maybe it will work, but I think it will be small.

Instead of using a general-purpose virtual machine like Cairo, we built a custom virtual machine. It's like building a dedicated processor to execute a specific program. Instead of using the Cairo language, we customized the virtual machine. This virtual machine is specifically designed to build zkEVM, just like designing a computer that can only run a single program.

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

Jordi Baylina：Polygon uses 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. Starknet uses Cairo, which is not just EVM.

About OP Rollup and zkEVM track

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

Jordi Baylina：OP Rollups was a good solution when ZK Rollup was not fully ready. But now that ZK Rollup is ready, I don’t think it makes much sense to use OP Rollups. Two years ago when zkEVM was still being built, everyone thought it would take about five years of work, so OP Rollups might be a very reasonable choice in these five years. But after only two years, zkEVM has made great progress and we have reached that goal ahead of schedule.

One of the big differences between OP Rollups, Starknet, and Polygon zkEVM is that Polygon zkEVM is the only one of the three that actually implements zkEVM and is 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, and it is not EVM. Starknet is not compatible with Ethereum.

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

Jordi Baylina: The main thing is that when we put all the tools and technologies together, their combined effect played a key role. This is an engineering process, like putting many known parts together. We have proven that this is possible to some extent, and solved many challenges in the process.

For example, in terms of proof time and the data centers required to calculate the proof, we initially needed hours. Now, it takes only a minute to build a proof on a large machine. So, you can see the progress in the past two years. It's not a single factor, as I said before, for example, we moved from a large prime field to a small prime field, we adopted STARKS, accelerated the hash function used in it, we learned how to do arithmetic processing and how to implement keccak256 in circuits in an efficient way. We created a very good architecture that enables different teams to work in parallel. We have a restriction layer, a cryptography layer, a ROM (read-only memory) layer, which is actually implementing 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 interact on Layer 2, and the gas fees are not much cheaper. Why is that?

Jordi Baylina: In terms of transferring assets between L1 and L2, that's not the case in Ethereum's zkEVM. From Layer 1 to Layer 2, it needs to go through two layers of processing. So you need to complete the transaction in Layer 1 for it to be finalized, which takes about 12 minutes.

I don't think there's any other reason than they're not doing it right. Right now it takes 12 minutes to deposit funds on the 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 that could fluctuate. That said, we know it's going to take an hour at most, but 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 I can tell you that in about six months, early next year, we plan to increase it again, to 50 times the current 10 times. The 50 times increase will mainly come from data compression, which is an area we're currently working hard on. The other 10 times will come from EIP-4844.

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

BlockBeats: Currently, the competition in the zkEVM track is very fierce. Polygon zkEVM, Consensys and scroll are all competing 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 a lot of similarities with us. Scroll is a zkEVM, and we are also zkEVM. But zkSync is not, it is a zkSolidity, and there is no EVM in the technical implementation process. And Starknet isn't even an EVM, it's more like a sidechain. But that doesn't mean they're good or bad, they're different things.

The zkEVM is an implementation of the EVM, which means you can use a zero-knowledge proof EVM. It's interchangeable, which means you should be able to use it in the exact same way as Ethereum. In the zkEVM space, we're talking about Scroll, Consensys (Linea), and Polygon zkEVM, which are arguably the three most advanced zkEVM projects out there, and we all have our pros and cons. Of course there's Taiko, but that's a Type 1 zkEVM.

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

Mainstream ZK Rollups and zkEVM technical architecture comparison, source: Dewhales Research (Note: Polygon Hermez is the current Polygon zkEVM)

I think the Consensys architecture is very similar to Polygon zkEVM. Both are very focused on state. The difference between them lies in the cryptography part. I think the lattice-based solution they adopt is very interesting. We can pay attention to how they implement it. Maybe this is an advantage. But from an architectural perspective, we are very similar. Scroll is a little different. Scroll doesn't have so many hierarchies. It is more simplified and cohesive.

Beats 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 cryptographic systems. A lattice is a set of linearly independent vectors in a multidimensional vector space. Lattice-based cryptography takes advantage of the difficulty of lattice problems, the most famous of which are the "Shortest Vector Problem" (SVP) and the "Closest Vector Problem" (CVP). These problems are usually difficult to solve in high-dimensional spaces, and even with modern computers, they require huge computing resources and time. 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 lattice problems, lattice-based cryptography is seen as a viable option to resist quantum computing attacks and is widely studied and applied.

BlockBeats: In your EDCON speech, you shared that the Polygon zkEVM team often communicates with "rival teams" such as Scroll. What topics do you mainly discuss? How do you view the competitive relationship between the two?

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

I don't think we are in competition, to be exact, at least not at the technical level, and we also try to avoid competition, which is what I talked about in the forum. We are not competing with anyone, but pursuing a cooperative attitude. This is a very complex technology, you have to put yourself at a higher level. I learn a lot from others and also teach others, this is our way forward. Of course, there may be competition at the product level, marketing and adjustment, but for users, this is not a bad thing.

About ZK Acceleration

BlockBeats：zkEVM also needs a sorter, right? Jordi Baylina: Currently zkEVM uses a centralized sorter. Like other sidechains, sidechains need sorters, which can be centralized or decentralized. Most sidechains currently use centralized sorters, but they also plan to build decentralized sorters. In Polygon, there is a mechanism called "Proof of Efficiency", but it is currently a centralized sorter, and we are working hard to find a better solution. BlockBeats: Will you launch a new token to decentralize the sorter? Jordi Baylina: We already have a token, MATIC, and there is no need to launch a new token. We already have an excellent, powerful, and valuable token. This token can be used in the consensus layer, such as Polygon PoS, and can also be used 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 am not responsible for this part in Polygon, there are other teams working on this issue at Polygon. I hope it can be achieved soon, but I am not sure, it may take six months or a year. It will not be a quick process, I don't think it will be implemented next month. But at least there is a whole team at Polygon dedicated to moving in this direction.

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

Jordi Baylina：Currently, the proof generator is very centralized, but in the future, a decentralized proof generator will be implemented. 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 processes need to be decentralized, and the key is the sorter. The proof generator is just a machine that performs calculations, nothing more.

BlockBeats: So there is an opportunity here?

Jordi Baylina: Yes, absolutely. It's not the time yet, but 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, and we see a Layer 2 ecosystem based on ZK, with many sidechains that can interact with each other. I'm not worried about the issues with proof generators, Ethereum governance, etc. I'm more worried about the sorter, and we need a decentralized sorter.