zkSync is built on ZK-Rollup architecture. In short, ZK-Rollup is an L2 scaling solution in which all funds are held by a smart contract on the main chain, while it performs computation and storage off-chain where the validity of the side chains is ensured by zero-knowledge proofs. For every Rollup block, a state transition zero-knowledge proof (SNARK) is generated and verified by the mainchain contract. This SNARK includes proof of the validity of every single transaction in the Rollup block. Additionally, the public data update for every block is published over the mainchain network in the cheap CALLDATA.