A zero-knowledge rollup is a Layer 2 blockchain solution that performs computations and storage off-chain while funds are held in a smart contract.
Simply put, zero-knowledge rollups or zk-rollups is a layer-2 scalability solution that allows blockchains to validate transactions faster while also ensuring that gas fees remain minimal. Zk-rollups manage to perform better than traditional layer-1 blockchains because they combine on and off-chain processes.
Zk-rollups are becoming increasingly popular both among developers who are looking to boost usability and among investors and traders looking for faster and cheaper transaction processing.
Users sign transactions and submit them to the prover, who verifies and queues them. Periodically, the prover batches thousands of transactions from the queue into a block and generates a zero-knowledge proof of their validity. This proof is a concise piece of data that can be verified in just a few milliseconds without revealing any transaction information. The prover then submits the proof and a small amount of data — such as the state root and the transaction root — to Ethereum as a single transaction. The smart contract verifies the proof and updates its state accordingly.
Withdrawing funds necessitates an exit request, which is submitted to an Ethereum block. The smart contract then unlocks and transfers the funds. No waiting period is required for withdrawals, as they are verified by proofs.
Factors that differentiate various types of zero-knowledge rollups include:
In zk-rollups, the term "zero-knowledge" refers to the use of zero-knowledge proofs for on-chain transaction verification without requiring interaction or trust. Zero-knowledge proofs are cryptographic proofs that can demonstrate a statement's truth without disclosing any information about the statement itself.
Lower Gas Fees: By generating zero-knowledge proofs for transaction batches and submitting minimal on-chain data, zk-rollups increase efficiency and decrease gas costs.
Higher Throughput: By circumventing base layer congestion and limitations, zk-rollups achieve faster transaction speeds and reduced confirmation times. Some estimates suggest zk-rollups can increase throughput by up to 100x.
Faster Confirmation Times: Users no longer need to wait for block confirmations on the base layer, which could take several minutes or hours depending on network conditions. Instead, they receive immediate feedback and finality on the layer-2 chain.
Privacy Features: Zk-rollups enhance transaction privacy by using zero-knowledge proofs to verify them on-chain without disclosing any information. This means minimal data is posted on-chain, and no information about the transactions is leaked. Zk-rollups also offer privacy features, such as concealing transaction amounts or recipients.
Proof Generation Cost: The cost of generating a zero-knowledge proof for a transaction batch depends on the complexity of the transactions, the proof system and the circuit design. Proof generation costs can be high for some use cases, potentially affecting zk-rollups' scalability and usability. Reducing proof generation costs involves using more efficient proof systems or circuit designs or subsidizing or incentivizing provers.
Circuit Complexity: This refers to the complexity of encoding and executing transactions on the layer-2 chain, depending on the circuit design and transaction functionality. High circuit complexity can affect zk-rollups' scalability and usability for certain use cases. Reducing circuit complexity involves using more optimized or specialized circuit designs or simplifying or standardizing transactions.
Compatibility Issues: Zk-rollups aren't fully compatible with existing smart contracts and tools running on Ethereum, necessitating changes or adaptations. Developers might need to use different languages, frameworks, libraries, or standards to write smart contracts for zk-rollups. Users might also need different wallets, browsers, or interfaces to interact with zk-rollups. Addressing compatibility issues involves using more interoperable or universal solutions or providing education and support for developers and users.
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