Data Availability Committee (DAC)

A DAC introduces an explicit trust assumption that a majority (or sometimes all) of its members are honest and will not collude to withhold data. This is a departure from the cryptoeconomic security of base layers like Ethereum, which rely on decentralized consensus and slashing. Users must trust the committee's integrity for data retrievability and, by extension, the ability to reconstruct the chain state and challenge invalid transactions.

DACs represent a deliberate trade-off, sacrificing some decentralization for significant scalability and cost benefits. The security model shifts from permissionless validation (anyone can verify) to permissioned attestation (only committee members sign). While faster and cheaper, this model is vulnerable to coordinated failure if the committee is compromised, whereas a fully decentralized data availability layer is resilient to individual node failures.

The security of a DAC hinges on its member selection and incentive structure.

• Members: Are typically well-known, reputable entities (exchanges, foundations, staking providers) to bootstrap trust.
• Bonding/Slashing: Members often post a cryptoeconomic bond that can be slashed for malicious behavior, such as signing for unavailable data.
• Legal Agreements: Operations may be backed by legal contracts, adding a layer of real-world accountability beyond blockchain-native mechanisms.

The primary attack vector is a data withholding attack, where the DAC refuses to provide the data needed to verify or challenge a rollup's state. Consequences include:

• Invalid State Finality: Users cannot prove fraud, potentially locking funds or accepting incorrect transactions.
• Censorship: The committee can selectively censor transactions by not making them available. Defenses include data availability sampling (DAS) by light clients and fallback mechanisms that trigger if attestations are missing.

Contrasting DACs with decentralized solutions highlights their security profile:

• Ethereum Data Availability (via blobs): Data is available if the chain is secure; trust is in the broader validator set.
• Celestia / Avail: Use data availability sampling and erasure coding, allowing light clients to probabilistically verify availability without trusting a small committee.
• DAC: Offers higher throughput and lower cost but concentrates trust in a known, fixed set of signers.

To mitigate centralization risks, many systems are evolving beyond pure DAC models:

• Hybrid DACs: Combine committee signatures with cryptoeconomic guarantees or partial data posting to a base layer.
• Progressive Decentralization: Start with a DAC for launch speed, with a clear roadmap to migrate to a permissionless data availability layer over time.
• Multi-Committee Designs: Use multiple, independent committees for redundancy, reducing reliance on any single group.

A cryptographic technique where light nodes randomly sample small, random chunks of block data to probabilistically verify its availability with high confidence, without downloading the entire block. This is the core innovation enabling scalable data availability layers like Celestia and is fundamental to Ethereum's danksharding roadmap. It allows networks to securely scale block size without requiring all participants to store all data.

A specialized blockchain or network layer whose primary function is to guarantee that transaction data for a rollup or execution layer is published and accessible. It decouples data publication from consensus and execution. Key examples include:

• Celestia: A modular network optimized for ordering and DA.
• EigenDA: A restaking-based DA layer built on Ethereum.
• Avail: A DA-focused blockchain from Polygon. These layers provide a cost-effective and scalable resource for rollups.

A cryptographic proof, such as a ZK-SNARK or ZK-STARK, that attests to the correct execution of a batch of transactions. For ZK-rollups, the validity proof is submitted to the main chain (e.g., Ethereum L1). Crucially, the security of a validity-proof rollup does not depend on data availability if the proof system is trusted. However, to allow users to reconstruct state and exit, the data is still typically published to a DA layer.

A cryptographic proof that demonstrates a state transition was executed incorrectly. Used by Optimistic Rollups. The security model of an optimistic rollup is entirely dependent on data availability; if the transaction data for a disputed state transition is not available, honest validators cannot construct a fraud proof, allowing an invalid state to be finalized. This makes a robust DA guarantee (via committees, layers, or the L1) critical.

A consensus mechanism where a known, permissioned set of validators (a committee) is responsible for ordering transactions and attesting to data availability. A Data Availability Committee is a specific application of this model for DA. Broader examples include Proof of Authority (PoA) networks and many sidechain implementations. It trades decentralization for higher performance and lower latency, making it suitable for enterprise or specific scaling solutions.

A data redundancy technique that expands the original data with parity chunks, allowing the full dataset to be reconstructed even if a significant portion of the chunks are missing. It is a prerequisite for Data Availability Sampling (DAS), as it ensures that any small random sample is representative of the whole. If a block producer withholds data, the erasure-coded blocks will have gaps, making the data un-reconstructible, which samplers can detect.