# Deneb -- Honest Validator **Notice**: This document is a work-in-progress for researchers and implementers. ## Table of contents - [Introduction](#introduction) - [Prerequisites](#prerequisites) - [Helpers](#helpers) - [`BlobsBundle`](#blobsbundle) - [Modified `GetPayloadResponse`](#modified-getpayloadresponse) - [Protocol](#protocol) - [`ExecutionEngine`](#executionengine) - [Modified `get_payload`](#modified-get_payload) - [Beacon chain responsibilities](#beacon-chain-responsibilities) - [Block and sidecar proposal](#block-and-sidecar-proposal) - [Constructing the `BeaconBlockBody`](#constructing-the-beaconblockbody) - [ExecutionPayload](#executionpayload) - [Blob KZG commitments](#blob-kzg-commitments) - [Constructing the `BlobSidecar`s](#constructing-the-blobsidecars) - [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 ### `BlobsBundle` *[New in Deneb:EIP4844]* ```python @dataclass class BlobsBundle(object): commitments: Sequence[KZGCommitment] proofs: Sequence[KZGProof] blobs: Sequence[Blob] ``` ### Modified `GetPayloadResponse` ```python @dataclass class GetPayloadResponse(object): execution_payload: ExecutionPayload block_value: uint256 blobs_bundle: BlobsBundle # [New in Deneb:EIP4844] ``` ## 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. ```python 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` ##### ExecutionPayload `prepare_execution_payload` is updated from the Capella specs to provide the parent beacon block root. *Note*: In this section, `state` is the state of the slot for the block proposal _without_ the block yet applied. That is, `state` is the `previous_state` processed through any empty slots up to the assigned slot using `process_slots(previous_state, slot)`. *Note*: The only change made to `prepare_execution_payload` is to add the parent beacon block root as an additional parameter to the `PayloadAttributes`. ```python def prepare_execution_payload(state: BeaconState, safe_block_hash: Hash32, finalized_block_hash: Hash32, suggested_fee_recipient: ExecutionAddress, execution_engine: ExecutionEngine) -> Optional[PayloadId]: # Verify consistency of the parent hash with respect to the previous execution payload header parent_hash = state.latest_execution_payload_header.block_hash # Set the forkchoice head and initiate the payload build process payload_attributes = PayloadAttributes( timestamp=compute_timestamp_at_slot(state, state.slot), prev_randao=get_randao_mix(state, get_current_epoch(state)), suggested_fee_recipient=suggested_fee_recipient, withdrawals=get_expected_withdrawals(state), parent_beacon_block_root=hash_tree_root(state.latest_block_header), # [New in Deneb:EIP4788] ) return execution_engine.notify_forkchoice_updated( head_block_hash=parent_hash, safe_block_hash=safe_block_hash, finalized_block_hash=finalized_block_hash, payload_attributes=payload_attributes, ) ``` ##### Blob KZG commitments *[New in Deneb:EIP4844]* 1. The execution payload is obtained from the execution engine as defined above using `payload_id`. The response also includes a `blobs_bundle` entry containing the corresponding `blobs`, `commitments`, and `proofs`. 2. Set `block.body.blob_kzg_commitments = commitments`. #### Constructing the `BlobSidecar`s *[New in Deneb:EIP4844]* To construct a `BlobSidecar`, a `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 associated sidecar topic, the `blob_sidecar_{subnet_id}` pubsub topic. Each `sidecar` is obtained from: ```python def get_blob_sidecars(signed_block: SignedBeaconBlock, blobs: Sequence[Blob], blob_kzg_proofs: Sequence[KZGProof]) -> Sequence[BlobSidecar]: block = signed_block.message block_header = BeaconBlockHeader( slot=block.slot, proposer_index=block.proposer_index, parent_root=block.parent_root, state_root=block.state_root, body_root=hash_tree_root(block.body), ) signed_block_header = SignedBeaconBlockHeader(message=block_header, signature=signed_block.signature) return [ BlobSidecar( index=index, blob=blob, kzg_commitment=block.body.blob_kzg_commitments[index], kzg_proof=blob_kzg_proofs[index], signed_block_header=signed_block_header, kzg_commitment_inclusion_proof=compute_merkle_proof( block.body, get_generalized_index(BeaconBlockBody, 'blob_kzg_commitments', index), ), ) for index, blob in enumerate(blobs) ] ``` The `subnet_id` for the `blob_sidecar` is calculated with: - Let `blob_index = blob_sidecar.index`. - Let `subnet_id = compute_subnet_for_blob_sidecar(blob_index)`. ```python 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.