consensus-specs/specs/sharding/p2p-interface.md

Ethereum 2.0 Sharding -- Network specification

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

Table of contents

• Introduction
• New containers
  • ShardBlob
  • SignedShardBlob
• Gossip domain
  • Topics and messages
    • Shard blobs: shard_blob_{shard}
    • Shard header: shard_header

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.

New containers

ShardBlob

Network-only.

class ShardBlob(Container):
    # Slot and shard that this blob is intended for
    slot: Slot
    shard: Shard
    # The actual data. Represented in header as data commitment and degree proof
    data: List[BLSPoint, POINTS_PER_SAMPLE * MAX_SAMPLES_PER_BLOCK]

Note that the hash-tree-root of the ShardBlob does not match the ShardHeader, since the blob deals with full data, whereas the header includes the KZG commitment and degree proof instead.

SignedShardBlob

Network-only.

class SignedShardBlob(Container):
    message: ShardBlob
    # The signature, the message is the commitment on the blob
    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_{shard}	SignedShardBlob
shard_header	SignedShardHeader

The DAS network specification defines additional topics.

Shard blobs: shard_blob_{shard}

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

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

• [REJECT] blob.shard MUST match the topic {shard} parameter. (And thus within valid shard index range)
• [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 the first blob with valid signature received for the proposer for the (slot, 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.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, signed over the SSZ output of commit_to_data(blob.data).
• [REJECT] The blob is proposed by the expected proposer_index for the blob's slot.

TODO: make double blob proposals slashable?

Shard header: shard_header

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

TODO: validation conditions.