What Is ZK-Rollup?
Also known as: ZK Rollup, Zero-Knowledge Rollup, Validity Rollup
In short
A ZK-Rollup is a Layer 2 scaling solution that executes transactions in batches off the main blockchain and proves their correctness to the main chain with zero-knowledge proofs (validity proofs). It lowers transaction costs while benefiting from Ethereum's security.
In a ZK-Rollup, user transactions are collected by a sequencer and executed on the rollup. A prover then produces a single validity proof showing that hundreds or thousands of transactions updated the state correctly. This proof is sent to Ethereum along with the compressed data needed to reconstruct the transactions and is verified by a smart contract on the main chain. The blob data introduced with EIP-4844 has significantly lowered the cost of this data publication.
The fundamental difference from optimistic rollups is that the correctness of transactions is mathematically proven rather than assumed. For this reason, there is no need to wait for a long dispute period, and withdrawals to the main chain can be completed once the proof is verified; in optimistic rollups, this wait is generally about one week. ZKsync Era, Starknet, Scroll and Linea are examples of networks using this model.
Among its limitations are that proof generation requires intensive computation, the complexity of proof systems and the difficulty of achieving EVM compatibility. In addition, in many rollups the sequencer is operated by a single company and the contracts are upgradeable, which brings centralization and admin key risks.
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