# Deneb -- Honest Validator **Notice**: This document is a work-in-progress for researchers and implementers. ## Table of contents - [Introduction](#introduction) - [Prerequisites](#prerequisites) - [Helpers](#helpers) - [`get_blobs_and_kzg_commitments`](#get_blobs_and_kzg_commitments) - [Beacon chain responsibilities](#beacon-chain-responsibilities) - [Block and sidecar proposal](#block-and-sidecar-proposal) - [Constructing the `BeaconBlockBody`](#constructing-the-beaconblockbody) - [Blob KZG commitments](#blob-kzg-commitments) - [Constructing the `SignedBlobSidecar`s](#constructing-the-signedblobsidecars) - [Sidecar](#sidecar) ## Introduction This document represents the changes to be made in the code of an "honest validator" to implement Deneb. ## Prerequisites This document is an extension of the [Capella -- Honest Validator](../capella/validator.md) guide. All behaviors and definitions defined in this document, and documents it extends, carry over unless explicitly noted or overridden. All terminology, constants, functions, and protocol mechanics defined in the updated [Beacon Chain doc of Deneb](./beacon-chain.md) are requisite for this document and used throughout. Please see related Beacon Chain doc before continuing and use them as a reference throughout. ## Helpers ### `get_blobs_and_kzg_commitments` The interface to retrieve blobs and corresponding kzg commitments. Note: This API is *unstable*. `get_blobs_and_kzg_commitments` and `get_payload` may be unified. Implementers may also retrieve blobs individually per transaction. ```python def get_blobs_and_kzg_commitments(payload_id: PayloadId) -> Tuple[Sequence[BLSFieldElement], Sequence[KZGCommitment]]: # pylint: disable=unused-argument ... ``` ## Beacon chain responsibilities All validator responsibilities remain unchanged other than those noted below. ### Block and sidecar proposal #### Constructing the `BeaconBlockBody` ##### Blob KZG commitments 1. After retrieving the execution payload from the execution engine as specified in Capella, use the `payload_id` to retrieve `blobs` and `blob_kzg_commitments` via `get_blobs_and_kzg_commitments(payload_id)`. 2. Validate `blobs` and `blob_kzg_commitments`: ```python def validate_blobs_and_kzg_commitments(execution_payload: ExecutionPayload, blobs: Sequence[Blob], blob_kzg_commitments: Sequence[KZGCommitment]) -> None: # Optionally sanity-check that the KZG commitments match the versioned hashes in the transactions assert verify_kzg_commitments_against_transactions(execution_payload.transactions, blob_kzg_commitments) # Optionally sanity-check that the KZG commitments match the blobs (as produced by the execution engine) assert len(blob_kzg_commitments) == len(blobs) assert [blob_to_kzg_commitment(blob) == commitment for blob, commitment in zip(blobs, blob_kzg_commitments)] ``` 3. If valid, set `block.body.blob_kzg_commitments = blob_kzg_commitments`. #### Constructing the `SignedBlobSidecar`s To construct a `SignedBlobSidecar`, a `signed_blob_sidecar` is defined with the necessary context for block and sidecar proposal. ##### Sidecar Blobs associated with a block are packaged into sidecar objects for distribution to the network. Each `sidecar` is obtained from: ```python def get_blob_sidecars(block: BeaconBlock, blobs: Sequence[Blob]) -> Sequence[BlobSidecar]: return [ BlobSidecar( block_root=hash_tree_root(block), index=index, slot=block.slot, block_parent_root=block.parent_root, blob=blob, kzg_commitment=block.body.blob_kzg_commitments[index], kzg_proof=compute_blob_kzg_proof(blob, block.body.blob_kzg_commitments[index]), ) for index, blob in enumerate(blobs) ] ``` Then for each sidecar, `signed_sidecar = SignedBlobSidecar(message=sidecar, signature=signature)` is constructed and published to the `blob_sidecar_{index}` topics according to its index. `signature` is obtained from: ```python def get_blob_sidecar_signature(state: BeaconState, sidecar: BlobSidecar, privkey: int) -> BLSSignature: domain = get_domain(state, DOMAIN_BLOB_SIDECAR, compute_epoch_at_slot(sidecar.slot)) signing_root = compute_signing_root(sidecar, domain) return bls.Sign(privkey, signing_root) ``` After publishing the peers on the network may request the sidecar through sync-requests, or a local user may be interested. The validator MUST hold on to sidecars for `MIN_EPOCHS_FOR_BLOB_SIDECARS_REQUESTS` epochs and serve when capable, to ensure the data-availability of these blobs throughout the network. After `MIN_EPOCHS_FOR_BLOB_SIDECARS_REQUESTS` nodes MAY prune the sidecars and/or stop serving them.