zkSync is a ZK rollup, a trustless protocol that uses cryptographic validity proofs to provide scalable and low-cost transactions on Ethereum. In zkSync, computation is performed off-chain and most data is stored off-chain as well. As all transactions are proven on the Ethereum mainchain, users enjoy the same security level as in Ethereum. Thanks to the combination of cutting-edge cryptography and on-chain data availability, ZK rollups (the core network of zkSync) are the only L2 scaling solution that doesn't require any operational activity to keep the funds safe.