Valium scaling solution

Validium is a scaling solution that enforces integrity of transactions using validity proofs like ZK-rollups, but doesn’t store transaction data on the Ethereum Mainnet.


Validiums are scaling solutions that use off-chain data availability and computation designed to improve throughput by processing transactions off the Ethereum Mainnet. Like zero-knowledge rollups (ZK-rollups), validiums publish to verify off-chain transactions on Ethereum. This prevents invalid state transitions and enhances the security guarantees of a validium chain.

These "validity proofs" can come in the form of ZK-SNARKs (Zero-Knowledge Succinct Non-Interactive Argument of Knowledge) or ZK-STARKs (Zero-Knowledge Scalable Transparent ARgument of Knowledge).

Funds belonging to validium users are controlled by a smart contract on Ethereum. Validiums offer near-instant withdrawals, much like ZK-rollups do; once the validity proof for a withdrawal request has been verified on Mainnet, users can withdraw funds by providing Merkle proofs. The Merkle proof validates the inclusion of the user’s withdrawal transaction in a verified transaction batch, allowing the on-chain contract to process the withdrawal.

However, validium users can have their funds frozen and withdrawals restricted. This can happen if data availability managers on the validium chain withhold off-chain state data from users. Without access to transaction data, users cannot compute the Merkle proof required to prove ownership of funds and execute withdrawals.

This is the major difference between validiums and ZK-rollups—their positions on the data availability spectrum. Both solutions approach data storage differently, which has implications for security and trustlessness.


1. Off-Chain Data Storage in Layer 2 Scaling Solutions

Layer 2 scaling methods like optimistic rollups and ZK-rollups balance scalability with security. Unlike purely off-chain protocols such as Plasma, these rollups publish some transaction data on the Layer 1 (L1) Ethereum network. This approach, however, limits their scalability due to Ethereum Mainnet's data bandwidth constraints. Data sharding is being explored to enhance Ethereum's data storage capabilities to address this issue.

Validiums offer a different approach to scalability by keeping all transaction data off-chain. They only post state commitments and validity proofs to the main Ethereum chain when updating the state. This method gives validiums a higher security level compared to other off-chain solutions like Plasma and sidechains, due to the presence of validity proofs. By minimizing the data Ethereum processes for validating off-chain transactions, validiums significantly improve throughput on the Mainnet.

2. Recursive Proofs in Blockchain

A recursive proof is a type of validity proof that verifies other proofs. These "proofs of proofs" are created by aggregating multiple proofs recursively until a final proof is formed that verifies all preceding proofs. Recursive proofs enhance blockchain processing speeds by enabling more transactions to be verified per proof.

In typical scenarios, each validity proof submitted by a validium operator to Ethereum confirms the integrity of a single block. However, a single recursive proof can validate several validium blocks simultaneously. This is achievable because the proving circuit can aggregate multiple block proofs into one comprehensive proof. When the on-chain verifier contract approves the recursive proof, all underlying blocks are instantly finalized.

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