zkRollup is a two-layer expansion scheme (layer2) based on zero-knowledge proof. The zkRollup scheme originated in the second half of 2018 and was proposed by Barry Whitehat and Vitalik successively. Rollup, as the name suggests, means "rolling up" and "summarizing", and packaging a large number of transactions "rolling up/summarizing" into one transaction. The principle of zkRollup can be explained in one sentence: complex calculations and proof generation are performed off-chain, The proof is verified on the chain and some data are stored to ensure data availability. zkRollup data availability allows anyone to restore the global state of the account according to the transaction data stored on the chain, thereby eliminating the security risks caused by data availability (the data availability here is compared to Plasma, the reason why Plasma cannot be called mainstream The expansion plan is that the data of Plasma is not submitted to the chain, so the cycle of withdrawing an asset on Plasma will be as long as about a week (dispute period). If no one submits a fraud certificate during the dispute, the asset can be withdrawn safely. to the main chain)