原文：《What’s New with ZKs?》by William M. Peaster
Compiled by: Kyle
If you’re deep into the world of crypto, you’ve been hearing about Zero Knowledge Proofs (ZK Proofs) and their applications for a while now. Are they live… or very close to live… or is a version of them just around the corner? It’s hard to keep track of this information.
ZK has a wide variety of implementations - today we’ll go through some updates on how things are developing in the ZK world.
How is ZK progressing?
In blockchain terms, we consider the initial stages of Ethereum’s life to be a monolith.
This means that for the first few years, the “Layer 1 (L1)” Ethereum mainnet is entirely responsible for executing its own transactions, facilitating its own network security, and servicing its own data availability.
Over the past few years, Ethereum has been rapidly moving towards a modular design, which means that external third-party solutions built around Ethereum are increasingly being used to scale Ethereum’s data and execution needs.
Modular Ethereum | Source: Ultra Scalable Ethereum
In terms of data availability, projects like Celestia and Polygon Avail are competitors. As for execution, in recent years we have seen the rise of “second layers (L2)” like Arbitrum and zkSync, which execute transactions outside of Ethereum (i.e., off-chain) and then efficiently “rollup” transactions into Ethereum L1, providing an incredibly affordable and fast user experience in the process.
Today, Ethereum L1 itself facilitates a measly ~30 transactions per second (TPS). In order to better handle global activity levels without severe network congestion (high fees, slow transactions), Ethereum is increasingly relying on scaling innovations to optimize its execution capabilities. There are two main types of solutions here: on-chain scaling and off-chain scaling.
On-chain scaling refers to changes made directly to a blockchain to increase its transaction execution capacity, or throughput speed. For Ethereum, one example is sharding, which, once implemented, will spread the load of activity across dozens of major, enshrined Ethereum chains, rather than a single mainnet.
The Future of Ethereum L2 + Sharding - Vitalik Buterin
Off-chain expansion refers to an external execution environment, or L2, which facilitates cheap and fast transactions outside of Ethereum, and then publishes transaction data in batches to Ethereum to complete the activity and inherit the security of Ethereum. Instead of splitting L1 into many main chains like sharding, off-chain expansion cultivates a secondary layer composed of many external rollups, which are very customizable.
ZK rollups: Leading off-chain scaling technology based on ZK
When it comes to L2, the most popular contemporary solution is zero-knowledge rollup (ZK rollup). Remarkably, these rollups can facilitate approximately 2,000 TPS, an increase of 6,500% over Ethereum’s current rate of 30 TPS!
This particular flavor of L2 uses “Zero-Knowledge Proofs (ZKP)” technology, such as SNARKs, to cryptographically verify and publish its batches of transactions on Ethereum. So, by combining off-chain execution with on-chain data via ZKP, you get ZK rollup (and conversely, combining off-chain execution with on-chain data via fraud proofs to get Optimistic rollup).
In summary, the five largest ZK rollups currently tracked by L2 BEAT are as follows:
dYdX — Cryptocurrency and derivatives exchange | $375M TVL Loopring Protocol — L2 for trading, NFTs | $121M TVL zkSync Lite — L2 for trading, NFTs | $65M TVL ZKSpace — L2 for trading, NFTs | $49M TVL Aztec Connect — L2 for private DeFI | $15M TVL Four of the top 10 L2s today are ZK rollups - from L2 BEAT
Today’s leading ZK rollups are built using StarkEx technology (e.g. dYdX and Loopring) or based on zkSync code (e.g. zkSync Lite and ZKSpace). However, there are many more ZK rollups that are not linked to these technology stacks that are worth your attention, such as Aztec Connect.
About Validiums and Volitions
However, ZK rollup is not the only notable ZK-based solution in the contemporary Ethereum scaling scene. Two other scaling approaches to note here are Validium and Volitions.
Validiums perform off-chain transactions and maintain their data via off-chain zero-knowledge proofs. This approach contrasts with how ZK rollups send data to Ethereum in batches (i.e. publish it on-chain). Where the data is stored, then, is the key difference between ZK rollups and validiums.
Validiums’ “dual off-chain” approach makes them ultimately custodial, as data is maintained by a trusted party. However, what validiums lack in trustlessness, they make up for in excellent performance, as the most powerful validiums today can facilitate +20,000 TPS.
Currently, two of the more well-known validium projects are Immutable X, an NFT-centric scaling solution with a TVL of $123 million, and Sorare, a fantasy sports digital card game with a TVL of $21 million. Other validators worth watching at the moment include ApeX, rhino.fi, and Myria.
As for Volitions, they are an innovation created by the StarkWare team that are a cross between ZK-rollup and validium. That is, users can choose between on-chain and off-chain data availability if they wish. This gives applications the option of TPS performance verification level while still being interoperable with non-custodial ZK-rollup technology. zkSync’s new groundbreaking zkPorter mechanism is an example of a volition system worth watching.
Image credit: Matter Labs zkEVM as the Holy Grail of Scaling
Consider how the architecture of a ZK-rollup consists of two main components: an on-chain Ethereum smart contract that receives and tracks L2 block data, and an off-chain virtual machine (VM) that serves as the execution environment for Ethereum-based transactions.
Well, zkEVM is a ZK-rollup compatible with the Ethereum Virtual Machine (EVM), the execution environment for Ethereum L1.
Illustration of the general extension method of Polygon zkEVM
At the beginning of the Ethereum scaling race, optimistic rollups like Arbitrum and Optimism had a huge advantage because this style of rollups was initially more easily compatible with or even completely equivalent to the EVM. This technical affinity makes it easy for applications to port their code and use their favorite tools to migrate from L1 to L2, which is a great UX.
In contrast, the nature of ZK-style scaling causes ZK rollups to start with a custom VM, meaning projects therefore require more extensive work to "interpret" code from the EVM or use new code written from scratch. However, as of March 2023, multiple ZK rollups projects are now apparently close to releasing their own zkEVM implementations!
The arrival of the zkEVM therefore represents a significant step forward in Vitalik Buterin’s 2021 prediction that “in the medium to long term, as the technology improves, ZK rollups will win out for all use cases.” ZK rollups have built-in privacy and security advantages over optimistic rollups due to their use of cryptographic proofs, so when you add EVM compatibility to the mix, it is possible that ZK rollups could outperform optimistic rollups in the future.
The ongoing competition between type 1 and type 2 zkEVM
The term “scaling wars” refers to the friendly, informal competition between optimistic rollups and ZK rollups teams to provide the best possible blockchain scaling solutions.
However, there is another competition within the ZK rollups space itself, an informal competition to see which team can implement the first “Type 1” and “Type 2” zkEVM as defined by Vitalik Buterin.
Buterin’s zkEVM Type
In an August 2022 blog post, Buterin provided a way to measure the capabilities of zkEVM projects by proposing a graded scale to rank them from Type 1 to Type 4. A Type 1 zkEVM would be completely equivalent to the EVM and could even be used to upgrade Ethereum itself, while a Type 4 zkEVM would only be compatible with certain Ethereum applications.
That said, Type 1 zkEVM implementations will be a while away due to all the work involved, but there are multiple projects working on Type 2 zkEVM right now.
Current major zkEVM efforts | Source: Immutable X
For example, the Polygon zkEVM is a Type 3 zkEVM and is on its way to becoming a Type 2 zkEVM, the EVM equivalent with some additional nuances. Scroll is another notable team currently building a Type 2 zkEVM. In contrast, zkSync Era (formerly zkSync 2.0) is an opinionated, intentional Type 4 zkEVM enhanced with custom functionality and the impressive willpower of zkPorter. Accordingly, the range of possibilities here is wide open.
zkEVM progress to date Source: Messari
Polygon zkEVM mainnet beta starts on March 27: https://twitter.com/0xPolygon/status/1625529122561597440
zkSync Era just launched mainnet to builders, user-friendly version coming soon: https://twitter.com/zksync/status/1626235292268240902
Scroll just released the Goerli zkEVM testnet, which is the last step before the mainnet launch: https://twitter.com/Scroll_ZKP/status/1630258973856395264
Starknet’s Kakarot zkEVM is already at Type 3 and accelerating: https://twitter.com/dimahledba/status/1606270836922585098
The Dawn of a New Blockchain UX Era
One day, Ethereum itself may upgrade to a Type 1 zkEVM for further on-chain scaling. In the meantime, external zkEVMs from Type 2 to Type 4 will continue to thrive as a complement to potential upgrades and provide unique customizations and UX enhancements to developers and users that Ethereum L1 cannot.
All in all, the end goal for the ZK rollups space (and arguably the entire L2 space) is zkEVM, and the first of these efforts is just around the corner. 2023 will be the year that everyday crypto users will be able to try out zkEVM for the first time, so if you want to get involved, keep an eye on Polygon, zkSync, Starknet, and Scroll as these teams’ latest scaling progress comes to life!
