Zero-knowledge rollups: how they work
A zero-knowledge rollup batches transactions and proves them valid to Ethereum. It aims to cut fees while Ethereum checks the validity proof.
Vahe HakobyanEditor-in-chief
Updated Oct 6, 20263 min readFact-checked
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- Validity proofs let Ethereum check a batch without re-running each transaction.
- You bridge in, transact, then withdraw to Ethereum.
- ZK rollups prove validity upfront; optimistic rollups use fraud challenges.
A zero-knowledge proof lets one party prove a statement is true without revealing anything beyond that truth. A rollup uses that idea to settle transactions on Ethereum.
How does a ZK rollup work?
The rollup collects transactions away from Ethereum and produces a validity proof for the batch. The proof is non-interactive, so Ethereum can verify it without re-running every transaction.
- Users send transactions to the rollup.
- The rollup groups them into a batch.
- A prover creates a validity proof.
- The rollup posts proof and data to Ethereum.
- Ethereum verifies and updates the state.
How do people use a ZK rollup?
You move assets from Ethereum to the rollup through a bridge. On the rollup you transact for lower fees, then withdraw back to Ethereum. Before you bridge, verify the rollup supports your token and the correct network.
How is it different from optimistic rollups?
Both types batch transactions and post data to Ethereum. A ZK rollup posts a validity proof for each batch. An optimistic rollup assumes batches are valid and allows fraud challenges.
What are the risks and limits?
Even with valid proofs, limits remain. Bridge contracts can have bugs, a sequencer can censor transactions, proving costs can be high, and withdrawals can face delays.
Frequently asked questions
Usually no. The proof hides the computation, not the transaction details, so amounts and addresses are usually public.
Yes, if the wallet supports the rollup's network. You usually add that network and switch to it.
It depends on the rollup and the bridge. Withdrawals can take time while the proof finalizes on Ethereum.
