Rollup Payload Lifecycle

How is a rollup’s payload (compressed batches of transactions or state transition diffs) encoded and made available on the EigenDA network?

flowchart TD
    subgraph Rollups[Rollup Domain]
        RS["Rollup Sequencer<br/>[Software System]<br/>Sequences the rollup; submits rollup payloads to EigenDA for data availability"]
        RV["Rollup Validator<br/>[Software System]<br/>Runs a derivation pipeline to validate the rollup"]
        Payload[("Rollup Payload<br/>[Data]<br/>Batches of tx data or state transition diffs")]
    end

    %% Standalone proxy
    Proxy["Proxy<br/>[Software System]<br/>Bridges domains by encoding/decoding payloads/blobs"]

    subgraph EigenDA[Data Availability Domain]
        EN["EigenDA Network<br/>[Software System]<br/>Provides decentralized data availability by storing and serving blobs"]
        Blob[("Blob<br/>[Data]<br/>Rollup payload encoded into bn254 field element array")]
        Cert[("DA Certificate<br/>[Data]<br/>Proof of Data Availability. Used to retrieve and validate blobs.")]
        ETH["Ethereum<br/>[Software System]<br/>Stores EigenDA network properties like operator stakes, etc. Also validates certs."]
    end

    %% Sequencer Flow
    RS -->|"(1) Creates"| Payload
    Payload -->|"(2) Sent to"| Proxy
    Proxy -->|"(3) Encodes into"| Blob
    Blob -->|"(4) Dispersed across"| EN
    EN -->|"(5) Verifies signatures according to stakes stored on"| ETH
    EN -->|"(6) Returns cert"| Proxy
    Proxy -->|"(7) Submits"| Cert
    Cert -->|"(8) Posted to"| ETH
    
    %% Validator Flow
    RV -->|"(9) Reads certificates"| ETH
    RV -->|"(10) Retrieve Compressed Batch from Certificate"| Proxy

    %% Styling
    classDef system fill:#1168bd,stroke:#0b4884,color:white
    classDef container fill:#23a,stroke:#178,color:white
    classDef data fill:#f9f,stroke:#c6c,color:black
    classDef red fill:#916,stroke:#714,color:white
    
    class RS,RV,EN,ETH,S1,Proxy system
    class Rollups,EigenDA container
    class Batch,Blob,Cert,D1 data

At a high-level, a rollup sequencer needs to make its payload available for download from validators of its network. The EigenDA network makes use of cryptographic concepts such as KZG commitments as fundamental building blocks. Because of this, it can only work with eigenda blobs (hereafter referred to simply as blobs; see technical definition below) of data. The EigenDA proxy is used to bridge the rollup domain (which deals with payloads) and the EigenDA domain (which deals with blobs).

As an example, an op-stack Ethereum rollup’s payload is a compressed batch of txs (called a frame). This frame gets sent to Ethereum to be made available either as a simple tx, or as a 4844 blob (using a blob tx). Using EigenDA instead of Ethereum for data availability works similarly: the payloads are encoded into an eigenda blob and dispersed to the EigenDA network via an EigenDA disperser. The disperser eventually returns a DA Certificate containing signatures of EigenDA operators certifying the availability of the data, which is then posted to Ethereum as the input field of a normal tx. Note that due to the rollup settling on Ethereum, Ethereum DA is needed, but only to make the DACert available, which is much smaller than the blob itself.

Data structs

Payload: piece of data that an EigenDA client (rollup, avs, etc.) wants to make available. This is typically compressed batches of transactions or state transition diffs.
EncodedPayload: payload encoded into a list of bn254 field elements (each 32 bytes), typically with a prefixed field element containing the payload length in bytes, such that the payload can be decoded.
PayloadPolynomial : encodedPayload padded with 0s to the next power of 2 (if needed) and interpreted either as evaluations (PolyCoeff) or coefficients (PolyEval) of a polynomial. Because the EigenDA network interprets blobs as coefficients, a PolyEval will need to be IFFT’d into a PolyCoeff before being dispersed.
(EigenDA) Blob: array of bn254 field elements of length a power of two. Interpreted by the network as coefficients of a polynomial. Equivalent to PolyCoeff.
Blob Header: contains the information necessary to uniquely identify a BlobDispersal request.
Blob Certificate: Signed BlobHeader along with relayKeys, which uniquely identify a relay service for DA Nodes to retrieve chunks from and clients to retrieve full blobs from.
Batch: Batch of blobs whose blob certs are grouped into a merkle tree and dispersed together for better network efficiency.
DA Certificate (or DACert): contains the information necessary to retrieve and verify a blob from the EigenDA network, along with a proof of availability.
AltDACommitment: RLP serialized DACert prepended with rollup-specific header bytes. This commitment is what gets sent to the rollup’s batcher inbox.

Contracts

EigenDACertVerifier: contains one main important function verifyCertV2 which is used to verify DACerts.
EigenDAThresholdRegistry: contains signature related thresholds and blob→chunks encoding related parameters.
EigenDARelayRegistry: contains an Ethereum address and DNS hostname (or IP address) for each registered Relay.
EigenDADisperserRegistry : contains an Ethereum address network for each registered Disperser.

Lifecycle phases

Sequencer:
- Encoding: Payload → Blob
- BlobHeader Construction: Blob → BlobHeader
- Dispersal: (Blob, BlobHeader) → Certificate
  - Certificate+Blob Validation
  - Unhappy path: Failover to EthDA
- Posting: Certificate → Ethereum tx
Validator (exact reverse of sequencer):
- Reading: Ethereum tx → Certificate
- Retrieval: Certificate → Blob
  - Certificate+Blob Validation
- Decoding: Blob → Payload

EigenDA Spec

Rollup Payload Lifecycle