What Are Zero Knowledge Rollups and How Do They Work?
What is a ZK rollup?
A ZK rollup, short for Zero Knowledge rollup, is a fix for blockchain scalability issues, especially for blockchains like Ethereum. It's a Layer 2 solution that runs on top of the existing Layer 1 blockchain. ZK rollups let you process more transactions per second and cut down on fees. Depending on how they're built, they can also boost privacy since not all info needs to be shared publicly. And they do all this without messing with the network’s security.
The "ZK" stands for Zero Knowledge, a cryptographic method that lets you prove something is true without showing all the details. That means transactions can be verified without revealing everything. So ZK rollups help with privacy and efficiency at the same time.
Instead of processing every transaction directly on the blockchain, ZK rollups bundle up lots of transactions into one rollup. Then only the proof, the Zero Knowledge proof, gets posted to the blockchain.
Key Takeaways
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ZK rollups help blockchains like Ethereum scale by combining lots of transactions into one.
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They process transactions off-chain, then post a Zero Knowledge proof to the main chain to confirm validity.
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Popular ZK rollups include zkSync, Starknet and Polygon zkEVM.
How do ZK rollups work?
ZK rollups move transaction processing off the main chain to ease the load. They work in three steps:
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Batching: Users make transactions and send them to the Layer 2 rollup.
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Off-chain processing: These transactions get processed off-chain and bundled into a batch.
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Zero Knowledge Proof: A cryptographic proof is made to show the batch is valid. This proof gets verified by a smart contract on the Layer 1 blockchain.
This way, thousands of transactions can be rolled into one and posted as a single transaction on-chain, helping scale things up. The rollup doesn’t record every single transaction, just the summary or ZK proof.
Imagine 1,000 users want to make a transaction on Ethereum at the same time. Instead of running 1,000 separate transactions, the ZK rollup makes one bundle and generates a cryptographic proof. That proof gets posted to the Ethereum blockchain. This saves a ton of computing power and gas fees.
Why are ZK rollups important?
ZK rollups fix one of blockchain’s biggest problems, scalability. When a network like Ethereum gets super popular, it can get overwhelmed. That means slower processing and higher fees.
ZK rollups help handle more transactions per second. Instead of Ethereum doing like 15 transactions per second, ZK rollups could push that number into the thousands. Since not all data has to go on-chain, gas costs drop too.
Because of Zero Knowledge proofing, transaction details stay private, while still being verifiable. There’s no need for a middleman to approve anything, cryptography guarantees that the batch is legit, which keeps things decentralized. Even though the actual transactions are processed off-chain, ZK rollups still benefit from the main chain’s security.
What’s the difference between ZK rollups and Optimistic rollups?
Both ZK rollups and Optimistic rollups are Layer 2 solutions, but they work differently. Like ZK rollups, Optimistic rollups also bundle transactions and process them off-chain. But instead of using cryptographic proofs, they just assume everything’s correct unless someone proves otherwise using fraud proofs.
Here’s a quick breakdown:
| Feature | ZK Rollups | Optimistic Rollups |
|---|---|---|
| Validation | Cryptographic proof (zero knowledge) | Assume it’s correct, with fraud challenge period |
| Speed | Fast finality, direct validation | Slower, because of challenge period |
| Privacy | High, hides transaction details | Less, transactions are visible |
| Gas fees | Lower, thanks to ZK proof | Higher, due to extra checks |
| Complexity | Technically harder to build | Easier and faster to deploy |
Examples of popular ZK rollup projects
There are already some big projects using ZK rollup tech. These projects are helping bring ZK rollups into the Ethereum ecosystem. Here are some popular ones:
zkSync
zkSync is one of the most well known ZK rollup platforms. It was built by Matter Labs and supports smart contracts. It’s focused on making Layer 2 user friendly for payments, DeFi and NFTs.
Starknet
Starknet is built for scalable dApps and supports complex smart contracts. It uses something called STARK proofs, which is a special type of Zero Knowledge cryptography. The company behind it, StarkWare, also made StarkEx, the engine behind dYdX and ImmutableX.
Polygon zkEVM
Polygon’s zkEVM is a ZK rollup that works with the Ethereum Virtual Machine. This makes it easy to move existing Ethereum dApps over to the Polygon zkEVM while keeping the smart contracts and tools intact.
Final thoughts
ZK rollups are a solid fix for blockchain scalability problems. By bundling transactions and handling them off-chain, they offer a powerful combo of efficiency, privacy and security. The tech is still evolving, but it’s already playing a big role for users and developers, and it's set to become even more important for Ethereum and other blockchains in the future.
