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eth2.0-specs/specs/sharding/p2p-interface.md

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Ethereum 2.0 Sharding -- Network specification

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

Table of contents

Introduction

The specification of these changes continues in the same format as the Phase0 and Altair network specifications, and assumes them as pre-requisite. The adjustments and additions for Shards are outlined in this document.

Constants

Misc

Name Value Description
SHARD_BLOB_SUBNET_COUNT 64 The number of shard_blob_{subnet_id} subnets used in the gossipsub protocol.

New containers

ShardBlobBody

class ShardBlobBody(Container):
    # The actual data commitment
    commitment: DataCommitment
    # Proof that the degree < commitment.length
    degree_proof: BLSCommitment
    # The actual data. Should match the commitment and degree proof.
    data: List[BLSPoint, POINTS_PER_SAMPLE * MAX_SAMPLES_PER_BLOCK]
    # Latest block root of the Beacon Chain, before shard_blob.slot
    beacon_block_root: Root

The user MUST always verify the commitments in the body are valid for the data in the body.

ShardBlob

class ShardBlob(Container):
    # Slot and shard that this blob is intended for
    slot: Slot
    shard: Shard
    # Shard data with related commitments and beacon anchor
    body: ShardBlobBody
    # Proposer of the shard-blob
    proposer_index: ValidatorIndex

This is the expanded form of the ShardBlobHeader type.

SignedShardBlob

class SignedShardBlob(Container):
    message: ShardBlob
    signature: BLSSignature

Gossip domain

Topics and messages

Following the same scheme as the Phase0 gossip topics, names and payload types are:

Name Message Type
shard_blob_{subnet_id} SignedShardBlob
shard_header SignedShardBlobHeader
shard_proposer_slashing ShardProposerSlashing

The DAS network specification defines additional topics.

Shard blob subnets

Shard blob subnets are used to propagate shard blobs to subsections of the network.

shard_blob_{subnet_id}

Shard block data, in the form of a SignedShardBlob is published to the shard_blob_{subnet_id} subnets.

def compute_subnet_for_shard_blob(state: BeaconState, slot: Slot, shard: Shard) -> uint64:
    """
    Compute the correct subnet for a shard blob publication.
    Note, this mimics compute_subnet_for_attestation().
    """
    committee_index = compute_committee_index_from_shard(state, slot, shard)
    committees_per_slot = get_committee_count_per_slot(state, compute_epoch_at_slot(slot))
    slots_since_epoch_start = Slot(slot % SLOTS_PER_EPOCH)
    committees_since_epoch_start = committees_per_slot * slots_since_epoch_start

    return uint64((committees_since_epoch_start + committee_index) % SHARD_BLOB_SUBNET_COUNT)

The following validations MUST pass before forwarding the signed_blob (with inner message as blob) on the horizontal subnet or creating samples for it.

  • [IGNORE] The blob is not from a future slot (with a MAXIMUM_GOSSIP_CLOCK_DISPARITY allowance) -- i.e. validate that blob.slot <= current_slot (a client MAY queue future blobs for processing at the appropriate slot).
  • [IGNORE] The blob is new enough to be still be processed -- i.e. validate that compute_epoch_at_slot(blob.slot) >= get_previous_epoch(state)
  • [REJECT] The shard blob is for the correct subnet -- i.e. compute_subnet_for_shard_blob(state, blob.slot, blob.shard) == subnet_id
  • [IGNORE] The blob is the first blob with valid signature received for the (blob.proposer_index, blob.slot, blob.shard) combination.
  • [REJECT] As already limited by the SSZ list-limit, it is important the blob is well-formatted and not too large.
  • [REJECT] The blob.body.data MUST NOT contain any point p >= MODULUS. Although it is a uint256, not the full 256 bit range is valid.
  • [REJECT] The proposer signature, signed_blob.signature, is valid with respect to the proposer_index pubkey.
  • [REJECT] The blob is proposed by the expected proposer_index for the blob's slot in the context of the current shuffling (defined by blob.body.beacon_block_root/slot). If the proposer_index cannot immediately be verified against the expected shuffling, the block MAY be queued for later processing while proposers for the blob's branch are calculated -- in such a case do not REJECT, instead IGNORE this message.

Global topics

There are two additional global topics for Sharding, one is used to propagate shard blob headers (shard_header) to all nodes on the network. Another one is used to propagate validator message (shard_proposer_slashing).

shard_header

Shard header data, in the form of a SignedShardBlobHeader is published to the global shard_header subnet.

The following validations MUST pass before forwarding the signed_shard_blob_header (with inner message as header) on the network.

  • [IGNORE] The header is not from a future slot (with a MAXIMUM_GOSSIP_CLOCK_DISPARITY allowance) -- i.e. validate that header.slot <= current_slot (a client MAY queue future headers for processing at the appropriate slot).
  • [IGNORE] The header is new enough to be still be processed -- i.e. validate that compute_epoch_at_slot(header.slot) >= get_previous_epoch(state)
  • [IGNORE] The header is the first header with valid signature received for the (header.proposer_index, header.slot, header.shard) combination.
  • [REJECT] The proposer signature, signed_shard_blob_header.signature, is valid with respect to the proposer_index pubkey.
  • [REJECT] The header is proposed by the expected proposer_index for the block's slot in the context of the current shuffling (defined by header.body_summary.beacon_block_root/slot). If the proposer_index cannot immediately be verified against the expected shuffling, the block 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.
shard_proposer_slashing

Shard proposer slashings, in the form of ShardProposerSlashing, are published to the global shard_proposer_slashing topic.

The following validations MUST pass before forwarding the shard_proposer_slashing on to the network.

  • [IGNORE] The shard proposer slashing is the first valid shard proposer slashing received for the proposer with index proposer_slashing.signed_header_1.message.proposer_index. The slot and shard are ignored, there are no per-shard slashings.
  • [REJECT] All of the conditions within process_shard_proposer_slashing pass validation.