Validium

Unlike ZK-Rollups, Validium does not post transaction data to the base layer (e.g., Ethereum). Instead, data is held by a committee or a Data Availability Committee (DAC). This reduces transaction costs drastically but introduces a trust assumption that the data will remain available for fraud proofs or state reconstruction.

• Primary Benefit: Extremely low transaction fees.
• Key Risk: Users cannot independently verify data availability, relying on the committee's honesty.

Every batch of transactions is cryptographically proven correct using a zero-knowledge proof (typically a ZK-SNARK or ZK-STARK). This validity proof is posted on-chain, guaranteeing the integrity of state transitions without revealing transaction details.

• Core Security: The base layer only needs to verify a small proof, not re-execute transactions.
• Result: Instant finality for withdrawals, as the state is proven, not disputed.

By moving both computation and data off-chain, Validium achieves significant scalability. Transaction processing is not bottlenecked by Layer 1 block space or gas costs.

• Performance: Can process thousands of transactions per second (TPS).
• Cost: Fees are primarily for proof generation/verification, not data publishing, making micro-transactions feasible.

A critical component where users must trust a set of known, often permissioned, entities to store and provide transaction data upon request. The DAC cryptographically attests to data availability.

• Function: Signs off on data for each batch; must provide data for state updates or fraud challenges.
• Trust Model: Introduces a crypto-economic or legal trust assumption distinct from pure cryptographic security.

Users can always exit to Layer 1 by submitting a Merkle proof of their funds. However, if the DAC withholds data, mass exits can be frozen, creating a censorship risk. Some implementations use proof-of-stake slashing or fraud proofs to penalize malicious committees.

• Exit Guarantee: Technically possible, but practically dependent on data availability.
• Contrast with Rollups: Rollups offer stronger censorship resistance as data is on-chain.

Ideal for high-frequency, low-value applications where ultimate Ethereum-level security is secondary to cost and speed.

• High-Volume DEXs & Gaming: Where micro-transactions are common.
• Private Transactions: ZK-proofs can hide amounts/participants; off-chain data adds privacy.
• Real Implementations: StarkEx (in Validium mode) by StarkWare, used by dYdX (v3) and Immutable X.

A core component of many Validium designs, a DAC is a set of trusted, known entities that sign off on the availability of off-chain transaction data. If a user needs to exit, they can request data from the committee.

Trade-offs:

• Pros: Enables very low costs and high throughput.
• Cons: Introduces a trust assumption; users must trust a majority of the committee members not to collude and withhold data.

A framework, popularized by StarkWare and adopted by others, that gives users or applications per-transaction choice between ZK-Rollup (data on-chain) and Validium (data off-chain) modes. This allows for granular control over the security-cost spectrum. A high-value NFT mint might use Rollup mode, while a game micro-transaction could use Validium mode.

Understanding the core differences between Validium and its closest relative, the ZK-Rollup.

Validium:

• Data Availability: Off-chain (DAC or PoS Guardians).
• Cost: Very low transaction fees.
• Throughput: Extremely high.
• Security: Requires trust in off-chain data availability mechanism.

ZK-Rollup:

• Data Availability: On-chain (calldata).
• Cost: Higher fees than Validium.
• Throughput: High, but limited by calldata costs.
• Security: Inherits Ethereum's security for both validity and data.

The core trade-off of a Validium is the sacrifice of on-chain data availability for higher throughput and lower costs. Unlike a ZK-Rollup, transaction data is stored off-chain by a committee or Data Availability Committee (DAC). This makes the system vulnerable if the committee withholds data, potentially freezing user funds, as the network cannot reconstruct the state to process withdrawals without this data.

A Data Availability Committee is a set of trusted entities that sign off on the availability of off-chain data. This introduces a trust assumption.

• Security Model: Users must trust that a supermajority of the DAC members (e.g., 7 of 10) are honest and available.
• Censorship Risk: A malicious majority could collude to censor transactions or withhold data.
• Mitigations: Committees often include reputable firms, and proofs of data possession may be used, but the trust model remains permissioned.

If a user suspects the DAC is malicious, they can initiate a challenge period (e.g., 7 days) to exit. However, this requires the user to prove data withholding, which is complex.

• Forced Exit: Users submit a fraud proof demonstrating the data is unavailable.
• Operational Burden: This places the security burden on watchful users, not the protocol.
• Contrast with Rollups: In a rollup, anyone can force a withdrawal using the permanently available on-chain data.

The primary benefit driving the security trade-off is performance.

• High Throughput: By not posting full transaction data to Ethereum, Validium networks can achieve ~9,000+ TPS, far exceeding base layer and rollup limits.
• Low Cost: Users pay minimal fees, as they avoid Ethereum's expensive calldata storage costs.
• Use Case: Ideal for high-frequency, low-value transactions (e.g., gaming, decentralized exchanges) where absolute censorship resistance is a secondary concern.

Volition is a hybrid architecture that lets users choose per-transaction between Validium mode (data off-chain) and ZK-Rollup mode (data on-chain).

• User-Choice Security: High-value transactions can opt for the stronger security guarantee of on-chain data availability.
• Flexibility: Provides a spectrum from pure Validium to pure Rollup, balancing cost and security dynamically.
• Example: StarkEx-powered applications like dYdX (v3) and Immutable X offer this volition model.

Validium and Optimistic Rollups represent different points on the scaling trilemma.

• Finality: Validium offers near-instant cryptographic finality via ZK proofs, unlike the 7-day challenge window of Optimistic Rollups.
• Data & Security: Optimistic Rollups post all data on-chain, providing stronger censorship resistance and decentralization.
• Cost: Validium is cheaper for applications but introduces the DAC trust assumption, while Optimistic Rollups pay higher data fees for stronger liveness guarantees.

A foundational scaling technology where transaction data is posted on-chain for data availability. Validium differs by keeping this data off-chain, using validity proofs (zk-SNARKs or zk-STARKs) to verify state transitions on the main chain.

• On-Chain Data: zk-Rollups post compressed data to Layer 1.
• Security Model: Inherits Ethereum's security for both execution and data.
• Example: Loopring, zkSync Era.

A trusted group of entities responsible for storing and providing the off-chain transaction data in a Validium. This is a key trust assumption in many Validium designs.

• Role: Sign attestations that data is available for users to reconstruct their state.
• Security Risk: If a DAC withholds data, users cannot withdraw funds, though state integrity remains proven.
• Alternative: Data Availability Sampling (DAS) with validium DA layers like Celestia or EigenDA reduces trust requirements.

A hybrid architecture that gives users a choice per transaction between zk-Rollup (on-chain data) and Validium (off-chain data) modes. This balances security and cost.

• Flexibility: Users opt for higher-cost, maximally secure posting or lower-cost, trust-minimized posting.
• Implementation: StarkEx (powering dYdX, Immutable X) popularized this model.
• User Sovereignty: Control over the data availability layer for individual assets or actions.

A competing Layer 2 scaling solution that uses fraud proofs instead of validity proofs. It assumes transactions are valid unless challenged during a dispute window.

• Data Availability: Like zk-Rollups, posts all transaction data on-chain.
• Latency vs. Finality: Offers faster inclusion but slower finality (7-day challenge period) compared to Validium's near-instant cryptographic finality.
• Example: Arbitrum, Optimism.

An off-chain scaling technique where participants lock funds in a smart contract and conduct numerous transactions privately, only settling the final state on-chain. Contrasts with Validium's batched, proof-based model.

• Use Case: Ideal for high-frequency, bidirectional exchanges (e.g., micro-payments, gaming).
• Privacy: All intermediate states are completely private.
• Limitation: Requires known, ongoing counterparties, unlike Validium's permissionless rollup model.

An earlier Layer 2 framework using fraud proofs and Merkle trees to create hierarchical child chains. It faced challenges with mass exits and data availability, problems that Validium and rollups address more effectively.

• Data Availability Problem: Users must monitor the chain to avoid losing funds, a key issue Validium's committee or DA layer aims to solve.
• Evolution: Many designs evolved into Optimistic Rollups or Validium-like constructions with explicit data solutions.