Crypto glossary
ZK-rollup
A ZK-rollup is a layer 2 network that bundles transactions off-chain and posts a zero-knowledge validity proof to Ethereum showing every batch is correct.
A ZK-rollup executes transactions outside the main chain, compresses them into batches and generates a cryptographic proof that the resulting state change follows the rules. A smart contract on Ethereum verifies the proof, so the main chain accepts the new state without re-running the transactions. An invalid batch cannot be finalised, because no valid proof exists for it.
zkSync, Starknet, Linea and Scroll are examples. Some aim for full compatibility with the EVM, while Starknet uses its own language, Cairo. Since validity is proven up front, withdrawals to Ethereum can complete once the proof is verified, often within hours rather than the week-long wait of optimistic rollups.
Generating proofs takes heavy computation, which adds cost and makes it harder to support every EVM feature. Proving systems are complex code that can contain bugs, and many ZK-rollups still depend on a single sequencer and on upgradeable contracts controlled by a small team.
Example
A ZK-rollup might pack 5,000 transfers into one batch and post a single proof to Ethereum, so the cost of verifying it is shared among all those users.
