The Key Role of zk-Rollups and zkEVM in Blockchain Evolution

Imagine you are standing in a long queue at a busy grocery store. The line moves slowly because there’s only one counter open for all customers. Wouldn’t it be great if the store could instantly open more counters, speeding up the entire process? zk Rollups and zkEVM work similarly, but for the digital world of blockchain. They help in making transactions quicker, cheaper, and more secure.

What is a ZK Rollup?

A ZK Rollup is a Layer 2 (L2) scaling solution functioning off the main Layer 1 (L1), frequently Ethereum, and soon Celestia. By operating off-chain, it sidesteps the congestion of blockspace on the L1. After processing transactions, a ZK Rollup submits either a batch of transaction data (in Optimistic Rollups) or a proof of execution (in ZK Rollups) to the L1 for final settlement. These L2 solutions inherit the security measures of their associated L1 since the data availability layer or settlement layer confirms the authenticity of the rollup.

Specifically, ZK Rollups employ validity proofs for scaling computations. They attach a cryptographic proof, like SNARKs, Kimchi, or STARKs, to each batch of transactions. An Ethereum smart contract, usually called an L2 bridge contract, then verifies this proof. Before finalizing a block, all Ethereum full nodes authenticate every transaction.

What is a zkEVM?

zkEVM stands for a virtual machine that runs EVM (Ethereum Virtual Machine) smart contracts, aligning them with ZKproof computation. But not all zkEVMs are the same; there are distinct variations:

• EVM-compatibility: This focuses on compatibility at the level of high-level programming languages like Solidity or Vyper.
• EVM-equivalence: This achieves compatibility at the EVM bytecode level and is consistent with Ethereum execution clients, such as Geth.
• Full-scale zkEVM: This achieves full compatibility at the EVM specification level.

However, all zkEVM variants integrate EVM in-circuit support, albeit with different compromises.

Here’s how they operate:

Firstly, to deploy to the Ethereum blockchain, smart contract codes, written in high-level languages (e.g., Solidity or Vyper), must be converted to EVM bytecode.

• EVM-compatibility: Here, code from Solidity or Vyper is converted into the VM’s bytecode. Following this, the execution trace’s legitimacy is verified in-circuit.
• EVM-equivalence: In this case, the EVM bytecode is either converted or interpreted into the VM’s bytecode. Afterward, the execution trace’s legitimacy is validated in-circuit.
• Full-scale zkEVM: Directly within the circuit, the validity of the EVM execution trace is ascertained.

Types of zkEVM Implementations

zkEVM comes in different flavors. Some aim for compatibility with Ethereum, while others focus on speed. If you’re building a new zkEVM, you have to make choices.

1. Compatibility-Focused zkEVM

Some zkEVMs aim to work hand in glove with Ethereum. They want to make it easier for developers to shift their projects onto this new express lane. But, the closer they stick to Ethereum, the less speedy they become.

2. Speed-Focused zkEVM

Others prefer speed and are willing to cut some corners for it. They might remove some complicated tasks to make the system run faster. It’s like removing speed bumps from the express lane, but at the cost of making some turns trickier to navigate.

Benefits of ZK-Rollups :

ZK-Rollups offer improved speed, reduced costs, and increased privacy in transactions.

• Lower Gas Fees: ZK-rollups use a method to bunch several transactions together. This method is more efficient and reduces the cost of gas, which is the fee for making a transaction.
• Higher Throughput: With zk-rollups, transactions are processed faster because they don’t get held up by the main network. Some experts believe zk-rollups can make transactions up to 100 times faster.
• Faster Confirmation Times: Once you make a transaction with zk-rollups, you get a quick response. You don’t have to wait for long periods, like on some other networks.
• Privacy Features: Zk-rollups keep transaction details hidden. Only the necessary information is shown on the main chain, ensuring that details like how much money was sent or who it was sent to remain private.
• Security and Integrity: Zk-rollups use Ethereum’s security systems. This means users don’t have to rely on or trust outside groups to handle their transactions or keep their information safe.

Challenges or Limitations of ZK-Rollups

While promising, ZK-Rollups face hurdles in cost, complexity, and compatibility.

• Proof Generation Cost: Making a zero-knowledge proof for a bunch of transactions can be pricey. The cost depends on how complex the transactions are. If these costs are too high, it might limit how many people use zk-rollups. One way to lower costs is to find better ways to make these proofs or give rewards to those who create them.
• Circuit Complexity: This is about how difficult it is to show and process transactions. If it’s too complex, it could slow down or limit zk-rollups. To fix this, we need better designs or simpler transactions.
• Compatibility Issues: Zk-rollups can’t work perfectly with all the tools and contracts on Ethereum right now. Developers might have to learn new ways to write contracts, and users might need different tools to use zk-rollups. To solve these issues, we need tools that work well together or to teach developers and users about the changes.

Technical Dive into zk-Rollups and zkEVMs

At the core of zk-Rollups and zkEVMs are advanced cryptographic processes that ensure both scalability and security. zk-Rollups utilize zero-knowledge proofs (ZKPs), specifically zk-SNARKs or zk-STARKs, to batch process transactions off-chain while maintaining a level of trust. 

These cryptographic proofs verify the correctness of computations without revealing the actual data involved. On the other hand, zkEVMs take this a step further by incorporating the Ethereum Virtual Machine (EVM) capabilities into zero-knowledge proof circuits. This integration enables the processing of smart contracts in a scalable yet secure manner. 

The technical novelty lies in the translation of EVM bytecode into zk-friendly computations while retaining compatibility with existing Ethereum tooling and contracts. Moreover, zkEVM projects like zkSync Era and Scroll explore the optimization of opcodes, gas models, and proof generation, striving to strike a balance between performance, compatibility, and security. 

The underlying cryptographic and computational advancements form the linchpin of these scaling solutions, promising not only higher throughput but also paving the path towards more robust and interoperable blockchain ecosystems. The meticulous design considerations encapsulated within zkEVM architectures spotlight the ingenious melding of cryptographic theory with practical blockchain utility, earmarking a notable stride in blockchain evolution.

Ethereum Needs zkEVMs !

Ethereum, a type of blockchain, sometimes faces high fees and long waits for transactions. Currently, it can only handle about 30 transactions every second. Rollups, a technology solution, can boost this by up to 2,000 transactions every second. Even after a major update to Ethereum (known as The Merge), rollups will likely still be used to help reduce congestion. One of the best things about zkEVMs, a type of rollup, is their ability to scale up.

Earlier rollup versions made things faster. But zkEVMs add privacy, security, and better compatibility to the mix. They work with the Ethereum system and can also work with Ethereum-like systems such as Avalanche, Solana, and Fantom. Plus, zkEVMs can drastically reduce the cost of transactions. Right now, a single Ethereum transaction costs around $0.90. But with zkEVMs, this can drop to under $0.01 for simple transactions. Big groups of transactions might cost just $0.10.

zkEVMs can also work with current Ethereum tools without needing changes. And they’re as secure as Ethereum itself.

Polygon and zkSync’s zkEVMs

In March 2023, the public saw the first two zkEVMs from zkSync and Polygon. zkSync introduced the first public zkEVM named zkSync Era. Polygon’s version was made available to everyone, and Ethereum’s founder, Vitalik Buterin, was the first to use it.

Many crypto projects are excited to use these new zkEVMs. However, it’s important to know they’re new and might have some issues to sort out over time. The teams behind them have warned users to be cautious for now.

The Future of zkEVMs on Ethereum

While zkSync and Polygon were the first, other companies are making their own zkEVMs, including Consensys, Scroll, and Taiko. Ethereum is trying to improve itself, but some changes can take a long time because they’re complex. In the meantime, zkEVMs offer a good way to handle some of Ethereum’s challenges, like speed, security, and functionality.

Notable zkEVM Projects

Let’s talk about some key projects that are shaping this technology.

Polygon zkEVM:

Polygon acquired the ZK rollup project Hermez, marking its commitment to its zkEVM project named Polygon zkEVM. This type 3 zkEVM implementation emphasizes performance, with modifications to opcodes, precompiled contracts, and the introduction of zk-counters. Developers benefit from its support for popular libraries like Web3.js and Ethers.js. The Proof of Efficiency (PoE) mechanism enhances security against harmful attacks. Polygon zkEVM stands out for its rapid network finality and affordable transaction fees.

ZkSync Era:

ZkSync Era, a type 4 zkEVM project, implements major changes to the EVM for enhanced performance while accommodating most EVM contracts. It alters opcodes, gas models, and certain EVM instructions. Zk-SNARKs are integrated for swift proof generation. Besides scalability, ZkSync Era offers developers and users an easy shift with its backward compatibility.

Scroll:

Scroll is a type 1 zkEVM project aiming for complete Ethereum compatibility. It uses the GETH Ethereum client, ensuring it works well with Layer 1 dApps. Although compatibility is its strength, Scroll faces slower prover times. The Halo 2 library assists in efficient zero-knowledge proof creation. Scroll’s main goal is to smoothly connect L1 and L2 dApps.

Conclusion

In the rapidly advancing world of blockchain, zk-Rollups and zkEVM stand out as vital innovations, addressing core challenges of scalability and transaction efficiency. As Ethereum and other blockchains grapple with congestion and high fees, these solutions not only enhance transaction throughput but also fortify security and interoperability. Their emergence signals a significant step forward, ensuring that blockchain platforms remain robust, cost-effective, and primed for future growth.