ZKrollups

ZkRollups are a class of layer-2 scaling solutions for blockchains that use zero-knowledge proofs to validate large numbers of off-chain transactions. In a zkRollup, a rollup operator processes transactions off-chain, updates a compressed state, and generates a cryptographic validity proof that the state transition is correct. The proof, together with a data commitment and a summary of the new state, is posted to the layer-1 blockchain. The layer-1 contract verifies the proof; if it checks out, the new state is accepted as final, allowing many transactions to be settled with far less on-chain data and gas than would be required for each transaction individually.

Data availability and verification are central to zkRollups. To ensure users can reconstruct the full transaction history, transaction data can be published on-chain or made accessible via data availability mechanisms. This design preserves decentralization and auditability while enabling high throughput. The cryptographic proof provides a strong validity guarantee, meaning the rollup’s state must be correct according to the off-chain computation.

Compared with optimistic rollups, zkRollups rely on validity proofs rather than fraud proofs and a dispute window, so finality is achieved more quickly after the proof is verified. Security models depend on the underlying zero-knowledge technology used, with implementations typically employing zk-SNARKs or zk-STARKs; the former often involves a trusted setup, while the latter generally does not.

Notable implementations include zkSync, Loopring, and StarkNet, among others, each adopting different zero-knowledge proof systems and optimizations. Main challenges include efficient proof generation, data availability strategies, and achieving broad compatibility with existing smart contracts and tooling.