validator.md

Deneb -- Honest Validator

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

Table of contents

• Introduction
• Prerequisites
• Constants
  • Misc
• Helpers
  • BlobsBundle
  • Modified GetPayloadResponse
• Protocol
  • ExecutionEngine
    • Modified get_payload
• 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.

Constants

Misc

Name	Value	Unit
BLOB_SIDECAR_SUBNET_COUNT	4	The number of blob sidecar subnets used in the gossipsub protocol.

Helpers

BlobsBundle

@dataclass
class BlobsBundle(object):
    commitments: Sequence[KZGCommitment]
    proofs: Sequence[KZGProof]
    blobs: Sequence[Blob]

Modified GetPayloadResponse

@dataclass
class GetPayloadResponse(object):
    execution_payload: ExecutionPayload
    block_value: uint256
    blobs_bundle: BlobsBundle

Protocol

ExecutionEngine

Modified get_payload

Given the payload_id, get_payload returns the most recent version of the execution payload that has been built since the corresponding call to notify_forkchoice_updated method.

def get_payload(self: ExecutionEngine, payload_id: PayloadId) -> GetPayloadResponse:
    """
    Return ExecutionPayload, uint256, BlobsBundle objects.
    """
    # 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, blob_kzg_commitments, and blob_kzg_proofs via get_payload(payload_id).blobs_bundle.
2. 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 associated sidecar topic, the blob_sidecar_{subnet_id} pubsub topic.

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)

The subnet_id for the signed_sidecar is calculated with:

• Let blob_index = signed_sidecar.message.index.
• Let subnet_id = compute_subnet_for_blob_sidecar(blob_index).

def compute_subnet_for_blob_sidecar(blob_index: BlobIndex) -> SubnetID:
    return SubnetID(blob_index % BLOB_SIDECAR_SUBNET_COUNT)

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.