validator.md

Deneb -- Honest Validator

Notice: This document is a work-in-progress for researchers and implementers.

Table of contents

• Introduction
• Prerequisites
• Helpers
  • get_blobs_and_kzg_commitments
• Beacon chain responsibilities
  • Block and sidecar proposal
    • Constructing the BeaconBlockBody
      • Blob KZG commitments
    • Constructing the SignedBlobSidecars
      • 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 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 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.

def get_blobs_and_kzg_commitments(
    payload_id: PayloadId
) -> Tuple[Sequence[Blob], Sequence[KZGCommitment], Sequence[KZGProof]]:
    # 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:

def validate_blobs_and_kzg_commitments(execution_payload: ExecutionPayload,
                                       blobs: Sequence[Blob],
                                       blob_kzg_commitments: Sequence[KZGCommitment],
                                       blob_kzg_proofs: Sequence[KZGProof]) -> 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) == len(blob_kzg_proofs)
    assert verify_blob_kzg_proof_batch(blobs, blob_kzg_commitments, blob_kzg_proofs)

3. If valid, set block.body.blob_kzg_commitments = blob_kzg_commitments.

Constructing the SignedBlobSidecars

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:

def get_blob_sidecars(block: BeaconBlock,
                      blobs: Sequence[Blob],
                      blob_kzg_proofs: Sequence[KZGProof]) -> 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=blob_kzg_proofs[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:

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.