In order to ensure efficient data management and secure verification, Ethereum has evolved from DA to DAS, and ultimately introduced PeerDAS.

Author: 0XNATALIE

At a recent Ethereum developer meeting, there was a proposal to split the Pectra hard fork of Ethereum into two parts. This proposal had been previously rejected due to concerns about delaying the Verkle tree upgrade. However, at this meeting, developers once again raised the idea because they wanted to include more improvement proposals (EIPs) in the Pectra fork. The proposal is to split the hard fork into two parts: the first part will include all EIPs currently on Pectra Devnet 3, and the second part of the fork will include EOF (EVM Object Format) and PeerDAS. To better understand PeerDAS, let's start with the fundamental concept of data availability.

DA: Ensuring nodes obtain on-chain data

Data Availability (DA) refers to ensuring that the blocks proposed by block proposers and all transaction data contained in the blocks can be effectively accessed and obtained by other network participants. Data availability is a key factor in blockchain security, as if the data is not available, even if the block is legitimate, other nodes cannot verify its content, which may lead to consensus issues and network attacks. For example, an attacker may only publish partial block data, causing other nodes to be unable to verify.

When a new block is broadcast, all participating nodes download and verify the block's data. This mode is feasible when the network scale is small, but as the blockchain continues to grow, the data volume becomes very large, and the storage requirements for each node increase, along with the hardware requirements. In order to allow light nodes (such as mobile devices like phones or computers) to participate in block verification, the blockchain has introduced sharding technology.

Sharding technology divides the entire blockchain network into multiple small "shards." Each shard only processes its own portion of the data and does not need to process the entire blockchain data. Therefore, a single node only needs to process the data of its own shard. However, each shard only processes a portion of the data, which means that nodes in other shards cannot directly access the complete data. How can we ensure that the data in the shards is available and that other nodes can verify the validity of this data? For example, a node in a shard may publish a newly generated block, but it may only publish a portion of the data. If other nodes cannot obtain all the data of the block, they cannot verify whether the block is truly legitimate.

DAS: Verifying overall data availability through partial data

To address the data availability issue in sharding, Data Availability Sampling (DAS) technology has been proposed, which aims to verify the data availability of blocks through sampling, without requiring each node to store or download the complete block data.

Data Availability Sampling allows nodes to verify data availability by randomly obtaining a portion of the block's data. If a node can successfully obtain and verify these random data segments, it can infer that the entire block's data is available.

To support this sampling verification, block data typically uses RS encoding. This encoding allows the complete data to be recovered even if only a portion of the data is received. Therefore, even if a node only downloads part of the block data, it can infer and confirm the validity of the entire block data. DAS reduces the amount of data that each node needs to process, allowing light nodes to participate in block verification.

DA layers such as Celestia achieve this through RS encoding + validity proof + DAS.

• RS Encoding (Reed-Solomon Encoding): This encoding allows nodes that receive only a portion of the data segments to reconstruct the entire data block. It is similar to error correction codes and has a certain fault tolerance, meaning that even if some data is lost, the remaining portion is sufficient to reconstruct the complete data.
• Validity Proof: Uses zero-knowledge proofs to ensure that there are no errors in the encoding and transmission of data. If the verification is successful, the entire data can be decoded without errors.
• DAS (Data Availability Sampling): By randomly sampling a portion of the RS encoded segments in a block, the availability of these segments is verified, thereby inferring the availability of the entire data block.

PeerDAS: Collaborative data verification between nodes

PeerDAS is a specific implementation of DAS, which performs data availability sampling through a peer-to-peer network, a network composed of multiple nodes that communicate directly. Under DAS, each node independently performs sampling verification of the data, while PeerDAS optimizes this process by allowing nodes to collaborate in sharing and verifying the data in the blocks, further improving verification efficiency. Nodes are not isolated from each other and can share the tasks and results of data verification, relying on the data already verified by other nodes. This means that nodes do not have to individually bear all the verification work, but can share the verification tasks through cooperation, further reducing the burden on nodes. Additionally, collaborative verification increases the difficulty of data tampering, as attackers would need to simultaneously affect multiple verification nodes to successfully tamper with the data.

Currently, according to the latest Ethereum meeting on PeerDAS, the Ethereum client Lighthouse team has merged the DAS branch into the main branch and is testing to ensure compatibility with PeerDAS. Branches are typically used to develop and test new features or improvements in independent code versions, and merging into the main branch means that this feature or improvement has been developed and is confident in its stability to be merged into the core code.

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