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ZK Meaning

Mar 22, 2024 | Updated Apr 9, 2024
Zero-Knowledge Rollups are layer-2 scaling solutions that moves computation workload and state storage outside the main blockchain.

What Are Zero-Knowledge Rollups?

The blockchain trilemma is arguably one of the most pressing concerns of blockchain technology. This is the concept that blockchain networks can’t seem to achieve the three key aspects of blockchain– decentralization, security, and scalability – all at once. Rollups– such as zk-rollups and optimistic rollups– allow blockchains to scale without sacrificing decentralization or security.

Zero-knowledge rollups, or simply zk-rollups, are blockchain solutions that handle transaction processing away from the base layer. Zk-rollups then record the transaction data on the main blockchain. This implies that the mainnet only stores transaction data rather than bulky transactions, enhancing network scalability and reducing transaction costs.

How Do ZK-Rollups Work?

When users submit transactions to the blockchain, the zk-rollup gathers them in batches. It then computes and validates all the transactions off-chain (such as transferring tokens and executing smart contracts). The batches are compiled into a single piece of data or summary representing all the transactions in the batch.

Upon processing the bundled transactions, the zk-rollup operator sends the summary to a zk-rollup smart contract on the main blockchain. The operator also generates cryptographic zero-knowledge proofs (ZKP) to “prove” or confirm the accuracy and validity of the state changes. The zero-knowledge aspect means that the party validating the transactions has “zero” knowledge regarding the transactions besides their validity.

Simply put, the validity proof confirms that the layer-2 blockchain has proposed the correct state changes. The mainnet nodes then verify the correctness of the submitted proofs rather than the transactions. If the proofs are correct, the main chain records the validity proof and finalizes the transactions in that batch.

Offloading its computational burden decongests the main chain– thereby increasing the number of transactions processed per second and lowering gas fees. 

Examples of zk-rollups include Polygon zkEVM, Scroll, zkSync, and StarkWare.

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