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Deneb -- Networking

This document contains the consensus-layer networking specification for Deneb.

The specification of these changes continues in the same format as the network specifications of previous upgrades, and assumes them as pre-requisite.

Table of contents

Configuration

Name Value Description
MAX_REQUEST_BLOCKS_DENEB 2**7 (= 128) Maximum number of blocks in a single request
MAX_REQUEST_BLOB_SIDECARS MAX_REQUEST_BLOCKS_DENEB * MAX_BLOBS_PER_BLOCK Maximum number of blob sidecars in a single request
MIN_EPOCHS_FOR_BLOB_SIDECARS_REQUESTS 2**12 (= 4096 epochs, ~18 days) The minimum epoch range over which a node must serve blob sidecars

Containers

BlobSidecar

class BlobSidecar(Container):
    block_root: Root
    index: BlobIndex  # Index of blob in block
    slot: Slot
    block_parent_root: Root  # Proposer shuffling determinant
    proposer_index: ValidatorIndex
    blob: Blob
    kzg_commitment: KZGCommitment
    kzg_proof: KZGProof  # Allows for quick verification of kzg_commitment

SignedBlobSidecar

class SignedBlobSidecar(Container):
    message: BlobSidecar
    signature: BLSSignature

BlobIdentifier

class BlobIdentifier(Container):
    block_root: Root
    index: BlobIndex

Helpers

verify_sidecar_signature

def verify_blob_sidecar_signature(state: BeaconState, signed_blob_sidecar: SignedBlobSidecar) -> bool:
    proposer = state.validators[signed_blob_sidecar.message.proposer_index]
    signing_root = compute_signing_root(signed_blob_sidecar.message, get_domain(state, DOMAIN_BLOB_SIDECAR))
    return bls.Verify(proposer.pubkey, signing_root, signed_blob_sidecar.signature)

The gossip domain: gossipsub

Some gossip meshes are upgraded in the fork of Deneb to support upgraded types.

Topics and messages

Topics follow the same specification as in prior upgrades.

The beacon_block topic is modified to also support deneb blocks and new topics are added per table below. All other topics remain stable.

The specification around the creation, validation, and dissemination of messages has not changed from the Capella document unless explicitly noted here.

The derivation of the message-id remains stable.

The new topics along with the type of the data field of a gossipsub message are given in this table:

Name Message Type
blob_sidecar_{index} SignedBlobSidecar (new)

Global topics

Deneb introduces new global topics for blob sidecars.

beacon_block

The type of the payload of this topic changes to the (modified) SignedBeaconBlock found in deneb.

blob_sidecar_{index}

This topic is used to propagate signed blob sidecars, one for each sidecar index. The number of indices is defined by MAX_BLOBS_PER_BLOCK.

The following validations MUST pass before forwarding the sidecar on the network, assuming the alias sidecar = signed_blob_sidecar.message:

  • [REJECT] The sidecar is for the correct topic -- i.e. sidecar.index matches the topic {index}.
  • [IGNORE] The sidecar is not from a future slot (with a MAXIMUM_GOSSIP_CLOCK_DISPARITY allowance) -- i.e. validate that sidecar.slot <= current_slot (a client MAY queue future sidecars for processing at the appropriate slot).
  • [IGNORE] The sidecar is from a slot greater than the latest finalized slot -- i.e. validate that sidecar.slot > compute_start_slot_at_epoch(state.finalized_checkpoint.epoch)
  • [IGNORE] The sidecar's block's parent (defined by sidecar.block_parent_root) has been seen (via both gossip and non-gossip sources) (a client MAY queue sidecars for processing once the parent block is retrieved).
  • [REJECT] The sidecar's block's parent (defined by sidecar.block_parent_root) passes validation.
  • [REJECT] The sidecar is from a higher slot than the sidecar's block's parent (defined by sidecar.block_parent_root).
  • [REJECT] The proposer signature, signed_blob_sidecar.signature, is valid as verified by verify_sidecar_signature.
  • [IGNORE] The sidecar is the only sidecar with valid signature received for the tuple (sidecar.block_root, sidecar.index).
  • [REJECT] The sidecar is proposed by the expected proposer_index for the block's slot in the context of the current shuffling (defined by block_parent_root/slot). If the proposer_index cannot immediately be verified against the expected shuffling, the sidecar MAY be queued for later processing while proposers for the block's branch are calculated -- in such a case do not REJECT, instead IGNORE this message.

Transitioning the gossip

See gossip transition details found in the Altair document for details on how to handle transitioning gossip topics for this upgrade.

The Req/Resp domain

Messages

BeaconBlocksByRange v2

Protocol ID: /eth2/beacon_chain/req/beacon_blocks_by_range/2/

The Deneb fork-digest is introduced to the context enum to specify Deneb beacon block type.

Per context = compute_fork_digest(fork_version, genesis_validators_root):

fork_version Chunk SSZ type
GENESIS_FORK_VERSION phase0.SignedBeaconBlock
ALTAIR_FORK_VERSION altair.SignedBeaconBlock
BELLATRIX_FORK_VERSION bellatrix.SignedBeaconBlock
CAPELLA_FORK_VERSION capella.SignedBeaconBlock
DENEB_FORK_VERSION deneb.SignedBeaconBlock

No more than MAX_REQUEST_BLOCKS_DENEB may be requested at a time.

BeaconBlocksByRoot v2

Protocol ID: /eth2/beacon_chain/req/beacon_blocks_by_root/2/

Per context = compute_fork_digest(fork_version, genesis_validators_root):

fork_version Chunk SSZ type
GENESIS_FORK_VERSION phase0.SignedBeaconBlock
ALTAIR_FORK_VERSION altair.SignedBeaconBlock
BELLATRIX_FORK_VERSION bellatrix.SignedBeaconBlock
CAPELLA_FORK_VERSION capella.SignedBeaconBlock
DENEB_FORK_VERSION deneb.SignedBeaconBlock

No more than MAX_REQUEST_BLOCKS_DENEB may be requested at a time.

BlobSidecarsByRoot v1

Protocol ID: /eth2/beacon_chain/req/blob_sidecars_by_root/1/

New in deneb.

The <context-bytes> field is calculated as context = compute_fork_digest(fork_version, genesis_validators_root):

fork_version Chunk SSZ type
DENEB_FORK_VERSION deneb.BlobSidecar

Request Content:

(
  List[BlobIdentifier, MAX_REQUEST_BLOB_SIDECARS]
)

Response Content:

(
  List[BlobSidecar, MAX_REQUEST_BLOB_SIDECARS]
)

Requests sidecars by block root and index. The response is a list of BlobSidecar whose length is less than or equal to the number of requests. It may be less in the case that the responding peer is missing blocks or sidecars.

The response is unsigned, i.e. BlobSidecar, as the signature of the beacon block proposer may not be available beyond the initial distribution via gossip.

No more than MAX_REQUEST_BLOB_SIDECARS may be requested at a time.

BlobSidecarsByRoot is primarily used to recover recent blobs (e.g. when receiving a block with a transaction whose corresponding blob is missing).

The response MUST consist of zero or more response_chunk. Each successful response_chunk MUST contain a single BlobSidecar payload.

Clients MUST support requesting sidecars since minimum_request_epoch, where minimum_request_epoch = max(finalized_epoch, current_epoch - MIN_EPOCHS_FOR_BLOB_SIDECARS_REQUESTS, DENEB_FORK_EPOCH). If any root in the request content references a block earlier than minimum_request_epoch, peers MAY respond with error code 3: ResourceUnavailable or not include the blob in the response.

Clients MUST respond with at least one sidecar, if they have it. Clients MAY limit the number of blocks and sidecars in the response.

BlobSidecarsByRange v1

Protocol ID: /eth2/beacon_chain/req/blob_sidecars_by_range/1/

New in deneb.

The <context-bytes> field is calculated as context = compute_fork_digest(fork_version, genesis_validators_root):

fork_version Chunk SSZ type
DENEB_FORK_VERSION deneb.BlobSidecar

Request Content:

(
  start_slot: Slot
  count: uint64
)

Response Content:

(
  List[BlobSidecar, MAX_REQUEST_BLOB_SIDECARS]
)

Requests blob sidecars in the slot range [start_slot, start_slot + count), leading up to the current head block as selected by fork choice.

The response is unsigned, i.e. BlobSidecarsByRange, as the signature of the beacon block proposer may not be available beyond the initial distribution via gossip.

Before consuming the next response chunk, the response reader SHOULD verify the blob sidecar is well-formatted and correct w.r.t. the expected KZG commitments through validate_blobs.

BlobSidecarsByRange is primarily used to sync blobs that may have been missed on gossip and to sync within the MIN_EPOCHS_FOR_BLOB_SIDECARS_REQUESTS window.

The request MUST be encoded as an SSZ-container.

The response MUST consist of zero or more response_chunk. Each successful response_chunk MUST contain a single BlobSidecar payload.

Clients MUST keep a record of signed blobs sidecars seen on the epoch range [max(current_epoch - MIN_EPOCHS_FOR_BLOB_SIDECARS_REQUESTS, DENEB_FORK_EPOCH), current_epoch] where current_epoch is defined by the current wall-clock time, and clients MUST support serving requests of blobs on this range.

Peers that are unable to reply to blob sidecar requests within the MIN_EPOCHS_FOR_BLOB_SIDECARS_REQUESTS epoch range SHOULD respond with error code 3: ResourceUnavailable. Such peers that are unable to successfully reply to this range of requests MAY get descored or disconnected at any time.

Note: The above requirement implies that nodes that start from a recent weak subjectivity checkpoint MUST backfill the local blobs database to at least epoch current_epoch - MIN_EPOCHS_FOR_BLOB_SIDECARS_REQUESTS to be fully compliant with BlobSidecarsByRange requests.

Note: Although clients that bootstrap from a weak subjectivity checkpoint can begin participating in the networking immediately, other peers MAY disconnect and/or temporarily ban such an un-synced or semi-synced client.

Clients MUST respond with at least the blob sidecars of the first blob-carrying block that exists in the range, if they have it, and no more than MAX_REQUEST_BLOB_SIDECARS sidecars.

Clients MUST include all blob sidecars of each block from which they include blob sidecars.

The following blob sidecars, where they exist, MUST be sent in consecutive (slot, index) order.

Slots that do not contain known blobs MUST be skipped, mimicking the behaviour of the BlocksByRange request. Only response chunks with known blobs should therefore be sent.

Clients MAY limit the number of blob sidecars in the response.

The response MUST contain no more than count * MAX_BLOBS_PER_BLOCK blob sidecars.

Clients MUST respond with blob sidecars from their view of the current fork choice -- that is, blob sidecars as included by blocks from the single chain defined by the current head. Of note, blocks from slots before the finalization MUST lead to the finalized block reported in the Status handshake.

Clients MUST respond with blob sidecars that are consistent from a single chain within the context of the request.

After the initial blob sidecar, clients MAY stop in the process of responding if their fork choice changes the view of the chain in the context of the request.

Design decision rationale

Why are blobs relayed as a sidecar, separate from beacon blocks?

This "sidecar" design provides forward compatibility for further data increases by black-boxing is_data_available(): with full sharding is_data_available() can be replaced by data-availability-sampling (DAS) thus avoiding all blobs being downloaded by all beacon nodes on the network.

Such sharding design may introduce an updated BlobSidecar to identify the shard, but does not affect the BeaconBlock structure.