How will PeerDAS improve Ethereum's data availability?

To ensure efficient data management and secure verification, Ethereum has evolved from DA to DAS, ultimately introducing PeerDAS.

Written by: 0XNATALIE

At a recent Ethereum developer meeting, a proposal was discussed to split the Ethereum Pectra hard fork into two parts. This proposal had previously been rejected due to concerns that it would delay the Verkle tree upgrade. However, at this meeting, developers revisited the idea because they wanted to include more improvement proposals (EIPs) in the Pectra fork. The proposal suggests dividing the hard fork into two phases: the first phase would include all EIPs currently on Pectra Devnet 3, while the second phase would include the EOF (EVM Object Format) and PeerDAS. To better understand PeerDAS, let's start with the fundamental concept of data availability.

DA: Ensuring Nodes Access On-chain Data

Data Availability (DA) refers to ensuring that the blocks published by block proposers, along with all transaction data contained within those blocks, can be effectively accessed and retrieved by other network participants. Data availability is a key factor in blockchain security, because if data is unavailable, even if a block is valid, other nodes cannot verify its contents, potentially leading to consensus issues and network attacks. For example, an attacker might only publish part of a block's data, making it impossible for other nodes to verify.

When a new block is broadcast, all participating nodes download and verify the block's data. This model works when the network is small, but as the blockchain grows, the amount of data becomes enormous, and each node's storage requirements increase, raising hardware demands. To allow light nodes (such as mobile phones or computers) to participate in block verification, sharding technology was introduced to blockchains.

Sharding divides the entire blockchain network into multiple smaller "shards." Each shard only processes its own portion of data and does not need to handle the entire blockchain's data. Therefore, a single node only needs to process the data of its own shard. However, since each shard only processes part of the data, nodes in other shards cannot directly access the complete data. So how can we ensure that the data in each shard is available and that other nodes can verify the validity of this data? For example, a node in a shard publishes a newly generated block but may only release part of the data. If other nodes cannot obtain all the block data, they cannot verify whether the block is genuine and valid.

DAS: Verifying Overall Data Availability Through Partial Data

To address data availability issues in sharding, Data Availability Sampling (DAS) technology was proposed. Its core idea is to verify the data availability of a block through sampling, without requiring each node to store or download the complete block data.

Data availability sampling allows nodes to randomly obtain only a portion of the block's data to verify data availability. If a node can successfully retrieve and verify these random data fragments, it can infer that the entire block's data is available.

To support this sampling verification, block data is usually encoded using RS encoding. This encoding allows the complete data to be recovered even if part of it is lost. Therefore, even if a node only downloads part of the block data, it can infer and confirm the validity of the entire block's data. DAS reduces the amount of data each node needs to process through sampling verification, enabling light nodes to participate in block verification.

DA layers such as Celestia implement these technologies. The main components are RS encoding + validity proof + DAS.

• RS Encoding (Reed-Solomon Encoding): This encoding method allows nodes that receive only part of the data fragments to reconstruct the entire data block. It is similar to error-correcting codes and has a certain degree of fault tolerance, so even if some data is lost, the remaining parts are sufficient to reconstruct the complete data.
• Validity Proof: Uses zero-knowledge proofs to ensure that there are no errors in the data during encoding and transmission. If the verification is successful, the entire data can be decoded without error.
• DAS (Data Availability Sampling): Light nodes randomly sample a portion of the RS-encoded fragments in a block to verify their availability, thereby inferring that the entire data block is available.

PeerDAS: Collaborative Data Verification Among Nodes

PeerDAS is a specific implementation of DAS that performs data availability sampling through a peer-to-peer network, which is composed of multiple nodes that communicate directly with each other. Under DAS, each node independently samples and verifies data, while PeerDAS optimizes this process by enabling nodes to collaborate in sharing and verifying block data, further improving verification efficiency. Nodes are not isolated; they can share data verification tasks and results, and rely on data already verified by other nodes. In this way, nodes do not have to bear all the verification work alone, but instead share the verification tasks through cooperation, further reducing the burden on each node. Moreover, collaborative verification increases the difficulty of data tampering, as an attacker would need to simultaneously compromise multiple verification nodes to successfully alter 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 usually independent code versions developed and tested for new features or improvements. Merging into the main branch means that the feature or improvement has been completed and is considered stable enough to be included in the core codebase.