Lumia L2, built using the Polygon Chain Development Kit (CDK), offers two configuration options: the Polygon zkEVM rollup and the Polygon CDK validium. This section focuses on the Polygon CDK validium configuration and its advantages for the Lumia L2 network.

What is Validium?

Validium is a scaling solution that leverages validity proofs to ensure the integrity of state transitions while storing transaction data off-chain. Unlike rollups, validium does not store transaction data on the Ethereum network, leading to reduced gas fees and improved scalability.

Lumia L2's Zero-Knowledge Validium Lumia L2's Polygon CDK validium is a zero-knowledge validium (zkValidium) that utilizes the Polygon zkEVM's off-chain prover to generate zero-knowledge proofs. These proofs are then published as validity proofs, adding a layer of trustlessness to the validium configuration.

The validium mode in Lumia L2 inherits all the components and functionalities of the Polygon zkEVM, except for the on-chain storage of transaction data. By storing only, a hash of the transaction data on the Ethereum network, Lumia L2's validium configuration offers significantly reduced gas fees compared to the zkEVM rollup option.

Data Availability Committee (DAC)

To manage the off-chain storage of transaction data, Lumia L2's Polygon CDK validium introduces the concept of a Data Availability Committee (DAC). The DAC is a set of trusted actors responsible for monitoring and authenticating the hash values proposed by the sequencer for publication on the Ethereum network.

The process works as follows:

  1. The trusted sequencer collects transactions from the pool DB, organizes them into batches, and computes the hash of the transaction data.

  2. The sequencer forwards the batch data and corresponding hash values to the DAC for authentication.

  3. DAC members independently verify the batch data against the received hash values and sign them upon validation.

  4. The sequencer collects the signatures from the DAC members and uses a multi-sig contract on the Ethereum network to attach the required signatures to the transaction data hash.

In essence, the Polygon CDK validium in Lumia L2 can be seen as a combination of the Polygon zkEVM and the DAC (Polygon CDK validium = Polygon zkEVM + DAC).

Validium Data Flow

The DAC and the sequencer work together to control the flow of data and state changes in Lumia L2's validium configuration. The process can be broken down into the following steps:

  1. Batch Formation: The sequencer collects user transactions, adds them to blocks, and organizes the blocks into batches while recursively computing their hash values.

  2. Batch Authentication: Once the batches are assembled and hash values computed, the sequencer forwards the batch data and corresponding hash values to the DAC for authentication.

  3. Data Validation and Storage: DAC nodes independently validate the batch data against the received hash values and store the validated hash values in their local databases for future reference.

  4. Signature Generation: Each DAC node generates a signature for each batch hash, endorsing the batch's integrity and authenticity.

  5. Communication with Ethereum: The sequencer collects the DAC members' signatures and the original batch hash, and submits them to the Ethereum network for verification.

  6. Verification on Ethereum: A designated multi-sig smart contract on Ethereum verifies the submitted signatures against each DAC member's known signatures and confirms that sufficient approval has been provided for the batch hash.

  7. Final Settlement with Zero-Knowledge Proof: The aggregator prepares a proof for the batch using the prover and submits it to the Ethereum network. This proof confirms the validity of the transactions in the batch without revealing transaction details, and the chain's state is updated on Ethereum.

By leveraging the Polygon CDK validium configuration, Lumia L2 achieves enhanced scalability, reduced gas fees, and a trustless environment for processing transactions while maintaining the security and integrity of the network. However, we are still wary of the centralised off-chain storage caveat that comes with validiums. This is where we go beyond typical Validium setup and create, in essence, our own private DA layer. Think Celestia, for ONLY Lumia.

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