Why Data Availability is the Next Major Attack Vector for ZKRs

ZKRs require data availability. A ZK proof validates a state transition, but users need the transaction data to reconstruct the state and exit. If this data is withheld, the rollup is a black box, even with a valid proof.

The sequencer is a single point of failure. Most rollups like Arbitrum and zkSync use a centralized sequencer for data posting. This creates a liveness dependency where a malicious or offline sequencer can freeze user funds indefinitely.

Ethereum is not a panacea. Posting data to Ethereum L1 via calldata or blobs provides strong guarantees but is expensive and slow. This cost forces a trade-off between security and scalability that most ZKRs optimize for the latter.

Alternative DA layers introduce new trust assumptions. Using Celestia, EigenDA, or Avail reduces costs but replaces Ethereum's consensus security with a weaker, often permissioned, validator set. This shifts the attack vector from L1 to the DA committee.

The exit game is broken. Without guaranteed data availability, the ZKR's fraud proof or validity proof mechanism is useless. Users cannot compute the correct state to challenge or withdraw, making the safety promise conditional on liveness.

Data withholding freezes assets. A malicious sequencer submits a valid zero-knowledge proof to L1, proving state updates are correct, but never publishes the raw transaction data. Users see their balances on L2 but cannot reconstruct proofs to withdraw funds, creating a permanent lock.

ZKRs are uniquely vulnerable. Optimistic rollups like Arbitrum and Optimism have a 7-day fraud-proof window to challenge invalid state. ZK rollups like zkSync and Starknet have instant finality; a valid proof is immediately accepted, making data availability the only security checkpoint.

The attack exploits economic incentives. Withholding data requires controlling the sequencer, which is profitable for high-value applications. This creates a credible threat for protocols like Aave or Uniswap v3 on ZK L2s, where TVL creates a massive ransom target.

Evidence: The Polygon Avail team quantified the risk, showing that without dedicated DA, a sequencer can profitably censor or withhold data for blocks containing over $2M in withdrawal value, making large DeFi pools primary targets.

The liveness assumption is critical. A ZK-Rollup's security collapses if its sequencer fails to post transaction data to L1. This is not a theoretical break of ZK cryptography but a practical liveness failure in the data availability layer.

Decentralized sequencers introduce new attack surfaces. Projects like Espresso Systems and Astria aim to solve this, but they create a new coordination game. Malicious actors can exploit the consensus mechanism of the sequencer set to censor or delay data posting.

Data availability sampling is not a panacea. While EigenDA and Celestia provide scalable DA, they introduce a trusted relay problem. The ZKR must trust that proven data is correctly relayed from the DA layer to the L1 verifier, creating a new bridge-like vulnerability.

Evidence: The Polygon zkEVM experienced a 10-hour downtime in March 2024 due to a sequencer failure, halting all L2 transactions despite the chain's cryptographic integrity being intact. This demonstrates the real-world impact of DA coordination failures.