176 lines
8.0 KiB
Markdown
176 lines
8.0 KiB
Markdown
# Ethereum 2.0 Sharding -- Network specification
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**Notice**: This document is a work-in-progress for researchers and implementers.
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## Table of contents
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<!-- TOC -->
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<!-- START doctoc generated TOC please keep comment here to allow auto update -->
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<!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE -->
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- [Introduction](#introduction)
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- [Constants](#constants)
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- [Misc](#misc)
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- [New containers](#new-containers)
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- [ShardBlobBody](#shardblobbody)
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- [ShardBlob](#shardblob)
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- [SignedShardBlob](#signedshardblob)
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- [Gossip domain](#gossip-domain)
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- [Topics and messages](#topics-and-messages)
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- [Shard blob subnets](#shard-blob-subnets)
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- [`shard_blob_{subnet_id}`](#shard_blob_subnet_id)
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- [Global topics](#global-topics)
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- [`shard_header`](#shard_header)
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- [`shard_proposer_slashing`](#shard_proposer_slashing)
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<!-- END doctoc generated TOC please keep comment here to allow auto update -->
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<!-- /TOC -->
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## Introduction
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The specification of these changes continues in the same format as the [Phase0](../phase0/p2p-interface.md) and
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[Altair](../altair/p2p-interface.md) network specifications, and assumes them as pre-requisite.
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The adjustments and additions for Shards are outlined in this document.
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## Constants
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### Misc
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| Name | Value | Description |
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| ---- | ----- | ----------- |
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| `SHARD_BLOB_SUBNET_COUNT` | `64` | The number of `shard_blob_{subnet_id}` subnets used in the gossipsub protocol. |
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## New containers
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### ShardBlobBody
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```python
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class ShardBlobBody(Container):
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# The actual data commitment
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commitment: DataCommitment
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# Proof that the degree < commitment.length
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degree_proof: BLSCommitment
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# The actual data. Should match the commitment and degree proof.
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data: List[BLSPoint, POINTS_PER_SAMPLE * MAX_SAMPLES_PER_BLOCK]
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# Latest block root of the Beacon Chain, before shard_blob.slot
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beacon_block_root: Root
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```
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The user MUST always verify the commitments in the `body` are valid for the `data` in the `body`.
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### ShardBlob
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```python
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class ShardBlob(Container):
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# Slot and shard that this blob is intended for
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slot: Slot
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shard: Shard
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# Shard data with related commitments and beacon anchor
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body: ShardBlobBody
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# Proposer of the shard-blob
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proposer_index: ValidatorIndex
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```
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This is the expanded form of the `ShardBlobHeader` type.
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### SignedShardBlob
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```python
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class SignedShardBlob(Container):
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message: ShardBlob
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signature: BLSSignature
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```
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## Gossip domain
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### Topics and messages
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Following the same scheme as the [Phase0 gossip topics](../phase0/p2p-interface.md#topics-and-messages), names and payload types are:
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| Name | Message Type |
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|----------------------------------|---------------------------|
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| `shard_blob_{subnet_id}` | `SignedShardBlob` |
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| `shard_header` | `SignedShardBlobHeader` |
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| `shard_proposer_slashing` | `ShardProposerSlashing` |
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The [DAS network specification](./das-p2p.md) defines additional topics.
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#### Shard blob subnets
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Shard blob subnets are used to propagate shard blobs to subsections of the network.
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##### `shard_blob_{subnet_id}`
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Shard block data, in the form of a `SignedShardBlob` is published to the `shard_blob_{subnet_id}` subnets.
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```python
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def compute_subnet_for_shard_blob(state: BeaconState, slot: Slot, shard: Shard) -> uint64:
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"""
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Compute the correct subnet for a shard blob publication.
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Note, this mimics compute_subnet_for_attestation().
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"""
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committee_index = compute_committee_index_from_shard(state, slot, shard)
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committees_per_slot = get_committee_count_per_slot(state, compute_epoch_at_slot(slot))
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slots_since_epoch_start = Slot(slot % SLOTS_PER_EPOCH)
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committees_since_epoch_start = committees_per_slot * slots_since_epoch_start
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return uint64((committees_since_epoch_start + committee_index) % SHARD_BLOB_SUBNET_COUNT)
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```
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The following validations MUST pass before forwarding the `signed_blob` (with inner `message` as `blob`) on the horizontal subnet or creating samples for it.
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- _[IGNORE]_ The `blob` is not from a future slot (with a `MAXIMUM_GOSSIP_CLOCK_DISPARITY` allowance) --
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i.e. validate that `blob.slot <= current_slot`
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(a client MAY queue future blobs for processing at the appropriate slot).
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- _[IGNORE]_ The `blob` is new enough to be still be processed --
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i.e. validate that `compute_epoch_at_slot(blob.slot) >= get_previous_epoch(state)`
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- _[REJECT]_ The shard should have a committee at slot --
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i.e. validate that `compute_committee_index_from_shard(state, blob.slot, blob.shard)` doesn't raise an error
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- _[REJECT]_ The shard blob is for the correct subnet --
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i.e. `compute_subnet_for_shard_blob(state, blob.slot, blob.shard) == subnet_id`
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- _[IGNORE]_ The blob is the first blob with valid signature received for the `(blob.proposer_index, blob.slot, blob.shard)` combination.
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- _[REJECT]_ As already limited by the SSZ list-limit, it is important the blob is well-formatted and not too large.
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- _[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.
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- _[REJECT]_ The proposer signature, `signed_blob.signature`, is valid with respect to the `proposer_index` pubkey.
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- _[REJECT]_ The blob is proposed by the expected `proposer_index` for the blob's slot
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in the context of the current shuffling (defined by `blob.body.beacon_block_root`/`slot`).
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If the `proposer_index` cannot immediately be verified against the expected shuffling,
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the block MAY be queued for later processing while proposers for the blob's branch are calculated --
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in such a case _do not_ `REJECT`, instead `IGNORE` this message.
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#### Global topics
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There are two additional global topics for Sharding, one is used to propagate shard blob headers (`shard_header`) to
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all nodes on the network. Another one is used to propagate validator message (`shard_proposer_slashing`).
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##### `shard_header`
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Shard header data, in the form of a `SignedShardBlobHeader` is published to the global `shard_header` subnet.
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The following validations MUST pass before forwarding the `signed_shard_blob_header` (with inner `message` as `header`) on the network.
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- _[IGNORE]_ The `header` is not from a future slot (with a `MAXIMUM_GOSSIP_CLOCK_DISPARITY` allowance) --
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i.e. validate that `header.slot <= current_slot`
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(a client MAY queue future headers for processing at the appropriate slot).
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- _[IGNORE]_ The `header` is new enough to be still be processed --
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i.e. validate that `compute_epoch_at_slot(header.slot) >= get_previous_epoch(state)`
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- _[IGNORE]_ The header is the first header with valid signature received for the `(header.proposer_index, header.slot, header.shard)` combination.
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- _[REJECT]_ The shard should have a committee at slot --
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i.e. validate that `compute_committee_index_from_shard(state, header.slot, header.shard)` doesn't raise an error
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- _[REJECT]_ The proposer signature, `signed_shard_blob_header.signature`, is valid with respect to the `proposer_index` pubkey.
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- _[REJECT]_ The header is proposed by the expected `proposer_index` for the block's slot
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in the context of the current shuffling (defined by `header.body_summary.beacon_block_root`/`slot`).
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If the `proposer_index` cannot immediately be verified against the expected shuffling,
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the block MAY be queued for later processing while proposers for the block's branch are calculated --
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in such a case _do not_ `REJECT`, instead `IGNORE` this message.
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##### `shard_proposer_slashing`
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Shard proposer slashings, in the form of `ShardProposerSlashing`, are published to the global `shard_proposer_slashing` topic.
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The following validations MUST pass before forwarding the `shard_proposer_slashing` on to the network.
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- _[IGNORE]_ The shard proposer slashing is the first valid shard proposer slashing received
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for the proposer with index `proposer_slashing.signed_header_1.message.proposer_index`.
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The `slot` and `shard` are ignored, there are no per-shard slashings.
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- _[REJECT]_ All of the conditions within `process_shard_proposer_slashing` pass validation.
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