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Learn: Why ZK-rollups need data availability?

Zero-knowledge rollups hold great promise for scaling blockchains, but the technology requires certain provisions to ensure its success.
​Zero-knowledge proofs have been hailed as a major advancement for blockchain technology, but the efficacy of these protocols will require streamlined data availability solutions to unlock their full potential.
Anurag Arjun, co-founder of Polygon and blockchain data availability protocol Avail, highlighted the importance of data availability for ZK-rollups in an interview with Cointelegraph.
​ZK-rollups are a layer-2 blockchain scaling solution for blockchain networks, allowing transactions to be batched and submitted to a layer-1 blockchain with the provision of a cryptographic proof. ZK-proofs aim to provide faster and more efficient transaction processing while maintaining the security of a blockchain system.
As Ethereum continues on its roadmap following its shift to proof-of-stake after the Merge, data availability is set to become an important factor in an increasing dependence on rollup scaling protocols for transaction batching and verification.
Arjun, who’s spearheading Avail’s growth following the platform’s spin-off from Polygon Labs, said that base-layer blockchain protocols of the future will have to optimize data availability for proofs, verifications and settlements rather than execution.
“If the execution is being scaled by layer 2s or rollups, the base layer then doesn’t have to worry about execution. They now have to optimize on things that they are used for, which is data availability.”
The transition sees blockchain technology moving from a “monolithic sort of blockchain architecture” to more modular setups like that of Avail, which provides infrastructure for ZK-rollups and other off-chain scaling solutions.
Arjun said that ZK-proofs are under-appreciated, given that they have removed the need for crypto-economic assumptions in blockchain systems:
“It changes the whole landscape: You no longer need these very heavy execution engines or validator run systems because you have ZKs that provide absolute execution proof guarantee. The only other thing that you require is data availability.”
The importance of data availability for ZK-proofs is tied to the nature of the technology, which essentially provides proof of a transaction or network state without revealing the data itself.
“That’s why it’s named a validity proof: It does not give any indication of what the data is like.”
Providing a protocol that handles data availability also addresses the current costs associated with submitting ZK-rollups and Optimistic Rollups to the Ethereum blockchain for example.
As Arjun explained, rollups face two primary costs in submitting transaction data and proof data, with up to 70% of today’s costs spent on storing transaction data on Ethereum. Transaction data submission costs and proof verification costs could be reduced significantly by using a base-layer data availability protocol.
Arjun added that proofs and data go hand in hand despite the fact that ZKs provide verifiable mathematical proofs or “absolute execution proof guarantee” on-chain without revealing data or the data needing to be verified.
This article first appeared in Cointelegraph, by Gareth Jenkinson​