Ethereum’s Rollup Race: What is a ‘True’ zkEVM?

Last week, a trio of announcements from Scroll, Matter Labs and Polygon all had something in common: Each company implied that it would be the “first” to bring a zkEVM to market.

This article originally appeared in Valid Points, CoinDesk’s weekly newsletter breaking down Ethereum’s evolution and its impact on crypto markets. Subscribe to get it in your inbox every Wednesday.

zkEVMs are a type of zero-knowledge (ZK) rollup – a “layer 2” network that runs atop Ethereum to process transactions, bundle them up and pass them back down to Ethereum’s layer 1 mainnet. ZK rollups use fancy cryptography to take some of the load off Ethereum’s highly trafficked layer 1 network. As a result, they promise to offer users cheaper transactions along with a host of other benefits.

Read more: The Sudden Rise of EVM-Compatible ZK Rollups

zkEVMs all aspire to the same goal: creating a ZK rollup experience that feels exactly like using Ethereum’s layer 1 blockchain. This means developers should be able to port over their existing smart contracts without changing their code and without abandoning the EVM (Ethereum Virtual Machine) tools that they are accustomed to using.

The EVM, rather than being one specific piece of hardware or software, is better understood as an amalgam of rules, standards and software packages. When shared across different computers running similar software, this shared set of standards coalesces into a network (Ethereum is one such network, although plenty of other blockchain networks have adopted versions of the EVM as well).

But how can three companies all claim to be the “first” to create a zkEVM? The answer comes down to how they each define what it means to create a true zkEVM.

zkEVMs

We won’t explain all of the different types of rollups in this article. For more on that – including the difference between Optimistic rollups and the more advanced ZK rollups discussed here – you can read last week’s edition of Valid Points and CoinDesk’s Layer 2 explainer.

Until now, zero-knowledge rollups have only been applied to a handful of use cases – like sending tokens between addresses or trading non-fungible tokens (NFTs). zkEVMs – zero-knowledge rollups that aim to support any Ethereum smart contract – were expected to be years away until just recently.

Compared quicker-to-market Optimistic rollups, general purpose zkEVMs offer a number of security and user experience benefits. In the future, they are expected to take over from Ethereum’s mainnet as the primary hub for Ethereum activity in the years to come.

Competing timelines

As for why three teams all seem to think they have the “first” zkEVM, it might be the case that they were genuinely unaware that their competitors were moving at a similar pace.

When Matter Labs said that it would be the first zkEVM to market in the first quarter of 2023, perhaps it didn’t realize Polygon was en route to launch its zkEVM test network as soon as this summer.

And maybe Polygon, when it announced that it would be the first zkEVM to market, didn’t realize zkSync was (apparently) prepared to launch on Ethereum’s mainnet by the end of this year – ahead of Polyon’s supposed plan to launch in early 2023.

Timelines in cryptoland are notoriously unreliable, and the roadmaps from Scroll, Matter Labs and Polygon should be taken with a grain of salt.

But timelines aren’t the only reason why Scroll, Matter Labs and Polygon all claim they will be the first zkEVM to market. Part of the disagreement comes down to how they define what makes a true zkEVM.

EVM-equivalent vs. EVM-compatible

Polygon faced criticism last week when it announced that it would be launching the first EVM-equivalent ZK rollup to market. According to some onlookers, Polygon’s solution would be better described as EVM-compatible, not EVM-equivalent.

So what is the difference between compatibility and equivalence?

The two leading Optimistic rollups for Ethereum, Artbitrum and Optimism, boast that they are EVM-equivalent. This means that the experience of developing on Arbitrum and Optimism is 100% identical to the experience of developing on Ethereum; developers have access to all of the same tools and frameworks that they use to develop on the Ethereum mainnet, and they won’t need to worry about their layer 1 contracts breaking if they are directly ported over to a layer 2 chain.

EVM-equivalence is a massive deal to developers since it means far less overhead when migrating from layer 1 to layer 2.

Users, too, see the benefits of EVM-equivalence. Rather than juggling rollup-specific wallets or other tools, users of EVM-equivalent chains, such as Optimism and Arbitrum, won’t need to abandon familiar apps like Metamask.

EVM-compatibility is a looser definition than EVM-equivalence. Rather than the developer and user experiences being exactly identical to that of Ethereum, EVM-compatible chains might not plug in to all of the same tools and software frameworks that are used on Ethereum.

Developers might need to rewrite their smart contracts in order to port them over to an EVM-compatible blockchain – sometimes in a completely different programming language than Ethereum’s native language, Solidity. Even if developers are still able to write their smart contracts using Solidity, certain operations might not be fully supported by the rollup, which can lead to bugs or other engineering headaches.

Although users might be able to send assets back and forth between the EVM-compatible rollup and Ethereum, doing so might require a specialized wallet rather than Metamask.

Is Polygon EVM-equivalent?

When Polygon announced that it would be bringing the first EVM-equivalent zkEVM to market last week, some onlookers pointed out that the specifications provided by Polygon would be better described as EVM-compatible, not EVM-equivalent.

In a June Twitter thread, Scroll’s Luozhu Zhang described three different types of zkEVMs: bytecode level, language level and consensus level. All of the applications announced last week fall into the first two categories.

zkSync 2.0 falls into the language-level bucket. Developers can write smart contracts in Solidity, but zkSync will transpile that code into another language called Yul behind the scenes, which it then interprets in order to do all of the fancy cryptography that powers the zero-knowledge rollup under the hood.

On the plus side, Matter Labs, the team behind zkSync, says that its system was engineered to provide the rollup certain advantages – particularly around how it generates computation-intensive cryptographic proofs.

On the negative end, zkSync, by most definitions, would be better described as EVM-compatible rather than EVM-equivalent. There’s a chance that zkSync won’t be 1:1 compatible with every single Ethereum tool out there, though Matter Labs insists that this shouldn’t be an issue in the long term.

Scroll and Polygon are both taking a bytecode-level approach to their zkEVMs.

These approaches rip out the transpiler step completely, meaning they don’t convert Solidity code into a separate language before it gets compiled and interpreted. This means better compatibility with the EVM. But even here, there are distinctions that may make Scroll more of a “true” zkEVM than Polygon, depending upon who you ask.

As Messari explained in a report released last week, “part of the [‘true’ EVM] debate follows whether the EVM bytecode is being executed directly or interpreted first and then executed. In other words, if a solution does not mirror official EVM specs, it cannot be considered a true zkEVM. Within this definition, Scroll might be considered a ‘true zkEVM’ vs. the others.”

According to Messari, “Polygon uses a new set of assembly codes to express each opcode, the human-readable translation of bytecode, which could allow the behavior of the code to be different on the EVM.”

In other words, Polygon might be a bit further from EVM equivalence than its main bytecode competitor, Scroll. Yet Polygon will argue that it’s precisely these differences that will allow it to provide a better product than its competitors.

Marketing in the metaverse

Last week’s zkEVM announcements represent impressive advances in technology, but, as crypto has proven time and time again, even highly technical concepts are not immune to marketing distortions.

At the end of the day though, slight technical distinctions – like the difference between EVM equivalence and compatibility – exist on a poorly defined spectrum.

As Scroll co-founder Sandy Peng told CoinDesk, “There isn't a clear consensus on any definitions. [Scroll’s] whole research team tends to gravitate towards a certain narrative or certain view on things, but it's by no means a definitive thing. There isn't even a consensus within our research team on what everything means.”

What’s even less clear (and probably less important) is who can rightfully claim to be the “first” zkEVM.

“‘First’ is a very philosophical concept,” Peng explained. “Whether you measure first being the first to announce or the first to start, or the first to achieve mainnet … it could be a couple of months or years to iron out all the kinks and debug.”

In the long term, it seems likely that all of the zkEVM solutions announced last week – along with several others we haven’t even heard about – will coalesce around new technologies and rollup solutions that make Ethereum vastly more accessible than it is today.

The competition around timelines and definitions is just a sideshow.

Pulse check

The following is an overview of network activity on the Ethereum Beacon Chain over the past week. For more information about the metrics featured in this section, check out our 101 explainer on Eth 2.0 metrics.

Disclaimer: All profits made from CoinDesk’s Eth 2.0 staking venture will be donated to a charity of the company’s choosing once transfers are enabled on the network.

Validated takes

Polygon deployed its EVM-compatible ZK rollup testnet.

• WHY IT MATTERS: The Polygon zkEVM would be the “first Ethereum-equivalent scaling solution that works seamlessly with all existing smart contracts, developer tools and wallets, harnessing advanced cryptography called zero-knowledge proofs,” said Polygon in a press release. Rollups like Polygon zkEVM are the main way the Ethereum community is working to boost the network’s capabilities – allowing users to transact quickly and cheaply without compromising the network’s most essential security guarantees. Read more here.

Tether sees a stable peg for the first time in over two months.

• WHY IT MATTERS: USDT, a stablecoin meant to be worth a dollar, regained its dollar peg on July 20, the first such instance since the collapse of Terra’s algorithmic stablecoin terraUSD. “The past two months have definitely been a stress test for stablecoins following the collapse of UST and sharp contraction in USDT’s market cap,” Clara Medalie, research director at crypto data provider Kaiko, said. “Tether proved its ability to process billions in redemptions, despite lingering questions over the makeup of its reserves.” Read more here.

“Cryptojacking” cases across the financial sector rose 269% in the first half of 2022.

• WHY IT MATTERS: According to a report by cybersecurity firm SonicWall, “Cryptojacking targeting the retail industry increased 63% year to date, while attacks on the financial industry skyrocketed 269%.” Cryptojacking, a type of cyberattack whereby hackers implant a piece of software that mines cryptocurrencies on a victim’s computer, “has a lower potential of being detected by the victim,” said Terry Greer-King, Sonicwall vice president for EMEA. Read more here.

Solana’s new daily address growth outpaced other blockchains.

• WHY IT MATTERS: Active wallets on the Solana network increased by 58% this year. New users peaked at over 400,000 in May before gradually declining to 240,000 users last week. These figures are a jump from December 2021’s levels of 150,000 to 170,000 new users each day, signaling growth and adoption. Despite the increased activity, total value locked on Solana DeFi applications slipped to $2.9 billion last week from May’s $6 billion figure. Read more here.

AntPool invested $10 million to support the Ethereum Classic ecosystem.

• WHY IT MATTERS: While the Ethereum network will convert to a proof-of-stake model, eliminating the need for specialized mining rigs, Ethereum Classic will continue to use mining rigs to mine its native ETC currency. The initial $10 million investment will fund the development and exploration of applications of the Ethereum Classic mainnet, as well as promote the overall performance of the network. Read more here.

Factoid of the week

Open comms

Valid Points incorporates information and data about CoinDesk’s own Ethereum validator in weekly analysis. All profits made from this staking venture will be donated to a charity of our choosing once transfers are enabled on the network. For a full overview of the project, check out our announcement post.

You can verify the activity of the CoinDesk Eth 2.0 validator in real time through our public validator key, which is:

0xad7fef3b2350d220de3ae360c70d7f488926b6117e5f785a8995487c46d323ddad0f574fdcc50eeefec34ed9d2039ecb.

Search for it on any Eth 2.0 block explorer site!