Data Availability
Data Availability Committees (“DACs”) have one core responsibility: to verify that the data necessary to reconstruct the L2 state from on-chain events is accessible to everyone. This availability means that, even if L2 operators go offline, users can still access their assets and data.
The Key to CDK-developed Chains: The DAC
In CDK-developed chains, the DAC, functioning as a secure consortium of nodes, ensures off-chain data access. This consortium is pivotal for the operation of CDK-developed chains, maintaining data availability even if chain operators go offline.
Polygon zkEVM: Powering Computation
CDK-developed chains are powered by Polygon zkEVM, offering a specialized environment for runtime and execution. This zkEVM-based engine is an exact implementation of the existing zkEVM. Operating as a zero-knowledge rollup (zk-rollup), it efficiently condenses numerous transactions into one batch, which is then submitted to Ethereum for validation.
Learn more about the roles and operation of zkEVM in the official documentation, available here.
Data Availability Layer: Ensuring Data Robustness
The DAC-managed Data Availability Layer, combined with the computational efficiency of Polygon zkEVM, ensures high-performance L2 blockchains within chains built with the CDK.
Advantages of the DAC Provided by Polygon CDK
The DAC primarily provides:
- Lower Transaction Fees: Reduced computational requirements lead to lower fees.
- State Privacy: Holding a secure copy of state transitions, ensuring data integrity.
zkEVM vs. Validium
The table below illustrates the key differences between Polygon's zkEVM and the Validium used in Polygon CDK.
| Feature | zkEVM | Validium |
|---|---|---|
| Transaction Data Storage | Stores all transaction data on L1 (Ethereum). | Only the hash of the transaction data is stored on Ethereum. |
| Data Availability | All data is available on-chain, providing high data availability. | Off-chain data availability is managed by the DAC, which authenticates the hashes of transaction data. |
| Security | Offers high security due to on-chain data availability and the use of Zero-Knowledge Proofs (ZKPs). | The off-chain data availability can potentially reduce security if DAC members collude to withhold state data. However, security is still maintained through the use of ZKPs. |
| Gas Fees | Higher, because all transaction data is stored on Ethereum. | Lower, because only the hash of the transaction data is stored on Ethereum. |
| Proof Generation | Uses Prover to generate ZKPs of batched transactions for validation. | Uses Prover to generate ZKPs of batched transactions for validation. |
| Transaction Validation | Validation is achieved through smart contracts on Ethereum. | Validation involves an additional layer where DAC members sign the hash of the transaction data. |
| Final Settlement | The transaction batches and their corresponding ZKPs are added to the Ethereum state. | The hash of transaction data and its ZKP are added to the Ethereum state, referred to as the Consolidated State. |
Data Flow in Polygon CDK
The DAC works closely with the Sequencer to ensure secure and efficient data handling. The process can be broken down as follows:
Batch Formation: The Sequencer collects user transactions and organizes them into batches.
Batch Authentication: Once the batches are assembled, they are authenticated. The Sequencer forwards the batch data and its corresponding hash to the DAC.
Data Validation and Storage: The DAC nodes each independently validate the batch data. Once validated, the hash is stored in each node's local database for future reference.
Signature Generation: Each DAC node generates a signature for the batch hash. This serves as an endorsement of the batch's integrity and authenticity.
Communication with Ethereum: The Sequencer collects the DAC members' signatures and the original batch hash and submits them to the Ethereum network for verification.
Verification on Ethereum: A designated smart contract on Ethereum verifies the submitted signatures against a list of valid DAC members and confirms that sufficient approval has been provided for the batch hash.
Final Settlement with ZKP: The Aggregator prepares a ZKP for the batch and submits it to Ethereum. This proof confirms the validity of the batch's transactions without revealing their details, thereby updating the CDK-developed chain state on Ethereum.
This process ensures a secure, efficient, and auditable flow of data through the system, supporting the implementation and operation of a CDK-developed chain in a broad range of contexts.
The following diagram illustrates the entire data flow process within Polygon CDK.
