Clear DefinitionsValidium
2 min read
Pronunciation
[vuh-lid-ee-uhm]
Analogy
Imagine a ZK-Rollup where the accountant provides the verifiable seal (validity proof) to the main office (Layer 1), proving all transactions were correct. In a Validium, the accountant still provides this seal, but the detailed transaction records themselves are not given to the main office; instead, they are kept by a separate, trusted group of record-keepers (the Data Availability Committee). This makes things even cheaper for the main office, but introduces trust in these record-keepers.
Definition
A Layer 2 scaling solution that uses validity proofs (like ZK-SNARKs or ZK-STARKs) to ensure transaction integrity, similar to ZK-Rollups, but keeps transaction data off-chain rather than posting it to Layer 1. Data availability is typically managed by a trusted Data Availability Committee (DAC) or other off-chain mechanism.
Key Points Intro
Validiums offer high scalability by moving both computation and data off-chain, relying on validity proofs for integrity and an external mechanism for data availability.
Key Points
Similar to ZK-Rollups in using validity proofs for state transitions.
Transaction data is kept off-chain, significantly reducing Layer 1 costs.
Data availability is ensured by a Data Availability Committee (DAC), a permissioned set of entities, or other off-chain solutions.
Offers higher throughput than ZK-Rollups that post data on-chain.
The security model relies on the honesty and availability of the data availability providers.
Example
StarkEx by StarkWare is a system that can be configured to operate in a Validium mode, often used for specific applications like exchanges or NFT marketplaces that require very high throughput.
Technical Deep Dive
In a Validium, the L1 smart contract verifies the validity proofs submitted by the operator, ensuring state transitions are correct. However, since transaction data is not on L1, users cannot directly reconstruct the state or force withdrawals from L1 using L1 data alone. They rely on the DAC or data provider to make the data available. If the DAC colludes and withholds data, users might not be able to create proofs to withdraw their funds, although the validity proofs prevent the operator from stealing funds directly by faking state transitions. This introduces a data availability risk that is not present in true rollups.
Security Warning
The primary risk in Validiums is data availability. If the Data Availability Committee (or equivalent mechanism) fails or becomes malicious and withholds data, users' funds could become frozen or stuck, even though the state transitions are proven valid. Trust in the DAC is essential.
Caveat
Validiums trade off the full data-on-chain security of ZK-Rollups for even greater scalability and lower costs by introducing a data availability assumption managed by a (typically permissioned) off-chain component.
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