ZK Rollup

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Basics

What is zk

zk=zero knowledge

More info:

Zero-knowledge proof⁠

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What is a ZK Rollup?

ZK Rollups are a layer 2 scaling solution that uses validity proofs to scale computation: each batch of transactions comes with a cryptographic proof (ZK-SNARK) that is verified by an Ethereum smart contract. This way every single transaction is fully verified by all Ethereum full nodes before a block is finalized.

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How secure is a ZK Rollup?

Out of all the scaling solutions, ZK Rollups are the most secure. They rely purely on math to fully inherit the security of L1, which is critical for function in highly adversarial environments. Other scaling solutions, instead, rely on economic guarantees or third parties, and thus offer far weaker security properties.

Validation of state changes in ZK Rollups is done through a: if any of the state changes is invalid the proof cannot be produced and, in turn, this means that the entity validating cannot include invalid state changes.

That’s why we call them sequencers and not validators: they don’t validate transactions, the Ethereum smart contract does by relying on pure math. We don’t need to trust them or monitor them for frauds, since they cannot commit any fraud.

How scalable is a ZK Rollup?

ZK Rollups can offer up to 2000 TPS at peak load! But it gets better.

ZK Rollups are also the only L2 scaling solution that can be extended with a system that can provide an entire order of magnitude more scale

How does ZK Rollup work?

In Layer 1, the bytecodes of the deployed smart contracts are stored in the Ethereum storage. Transactions will be broadcasted in a P2P network. For each transaction, each full node needs to load the corresponding bytecode and execute it on EVM to reach the same state (transaction will be used as input data).

In Layer 2, the bytecode is also stored in the storage and users will behave in the same way. Transactions will be sent off-chain to a centralized zkVM node. Then, instead of just executing the bytecode, zkVM will generate a succinct proof to prove the states are updated correctly after applying the transactions. Finally, Layer 1 contract will verify the proof and update the states without re-executing the transactions.

ZK Rollup Projects

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zkSync & zkSync 2.0⁠

ZK Rollup Optimization

proposing new zk-friendly primitives i.e.

Poseidon hash⁠

can achieve 100x efficiency than SHA256 in circuit.

Ongoing work on improving efficiency of general-purpose verifiable VMs, as in

TinyRAM⁠

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A growing number of general-purpose optimization tricks like Plookup, and even more generally faster cryptographic libraries.

Bibliography:

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https://zksync.io/zkevm/#what-is-zkevm-and-why-is-this-a-big-deal⁠

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