What Are Zk-Rollups?

Zero-knowledge rollups (Zk-rollups) are a type of Layer 2 scaling solution for blockchain networks. They are designed to enhance scalability

What Are Zk-Rollups?

Layer 2 scaling solutions, such as rollups, are designed to enhance the scalability and efficiency of blockchain networks. They achieve this by bundling (or rolling up) multiple transactions into a single batch to process them off-chain. Among the different types of rollups, zk-rollups (short for zero-knowledge rollups) stand out due to their unique properties and advantages.

How Do Zk-Rollups Work?

Zk-rollups “roll up” multiple (up to thousands) transactions into a single batch and then process them off-chain. This way, zk-rollups significantly reduce the workload on the parent chain, allowing for faster transaction processing and reduced fees. Some of the transactions handled off-chain include token transfers, contract interactions, and other activities that would normally occur directly on the Layer 1 network.

After aggregating these transactions, a zk-rollup scaling solution generates a zero-knowledge proof, typically a zk-Snark (Zero-Knowledge Succinct Non-Interactive Argument of Knowledge) or a zk-Stark (Zero-Knowledge Scalable Transparent Argument of Knowledge). These cryptographic proofs serve as mathematical guarantees that the batched transactions have been executed correctly off-chain without disclosing any transaction details.

Once the zero-knowledge proof is created, it is submitted on-chain, along with a minimal set of transaction data. This usually includes a state root (a snapshot of the overall state of the system after the batch of transactions has been processed) and a transaction root (which summarizes the batched transactions). These are submitted to a smart contract deployed on the Layer 1 blockchain.

The smart contract on the Layer 1 network verifies the validity of the zero-knowledge proof. Since the proof is mathematically sound, this verification process takes significantly less time and computational resources than processing each transaction. After the proof is verified, the Layer 1 blockchain updates its state to reflect the changes induced by the processed batch of transactions.

Popular examples of zero knowledge Layer 2 networks include Immutable X, zkSync and Linea, among others.