151 lines
7.7 KiB
Markdown
151 lines
7.7 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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- [Gossip domain](#gossip-domain)
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- [Topics and messages](#topics-and-messages)
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- [Shard block subnets](#shard-block-subnets)
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- [`shard_block_{subnet_id}`](#shard_block_subnet_id)
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- [Global topics](#global-topics)
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- [`shard_block_header`](#shard_block_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 network specifications of previous upgrades, 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_BLOCK_SUBNET_COUNT` | `64` | The number of `shard_block_{subnet_id}` subnets used in the gossipsub protocol. |
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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_block_{subnet_id}` | `SignedShardBlock` |
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| `shard_block_header` | `SignedShardBlockHeader` |
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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 block subnets
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Shard block subnets are used by builders to make their blobs available after selection by shard proposers.
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##### `shard_block_{subnet_id}`
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Shard block data, in the form of a `SignedShardBlock` is published to the `shard_block_{subnet_id}` subnets.
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```python
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def compute_subnet_for_shard_block(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_BLOCK_SUBNET_COUNT)
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```
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The following validations MUST pass before forwarding the `signed_block` on the horizontal subnet or creating samples for it.
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We define some aliases to the nested contents of `signed_block`:
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```python
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block: ShardBlock = signed_block.message
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signed_blob: SignedShardBlob = block.signed_blob
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blob: ShardBlob = signed_blob.message
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```
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- _[IGNORE]_ The `block` 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_block(state, blob.slot, blob.shard) == subnet_id`
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- _[IGNORE]_ The block is the first block with valid signature received for the `(block.proposer_index, blob.slot, blob.shard)` combination.
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- _[REJECT]_ The blob is not too large, the data MUST NOT be larger than the SSZ list-limit, and a client MAY be more strict.
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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 block proposer signature, `signed_block.signature`, is valid with respect to the `proposer_index` pubkey.
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- _[REJECT]_ The blob builder exists and has sufficient balance to back the fee payment.
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- _[REJECT]_ The blob builder signature, `signed_blob.signature`, is valid with respect to the `builder_index` pubkey.
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- _[REJECT]_ The block 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 `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 block'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.
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One is used to propagate shard block headers (`shard_block_header`) to all nodes on the network.
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Another one is used to propagate shard proposer slashings (`shard_proposer_slashing`).
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##### `shard_block_header`
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Shard header data, in the form of a `SignedShardBlockHeader` is published to the global `shard_block_header` subnet.
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Shard block headers select shard blob bids by builders, and should be timely to ensure builders can publish the full shard block timely.
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The following validations MUST pass before forwarding the `signed_block_header` (with inner `message` as `header`) on the network.
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We define some aliases to the nested contents of `signed_block_header`:
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```python
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block_header: ShardBlockHeader = signed_block_header.message
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signed_blob_header: SignedShardBlobHeader = header.signed_blob_header
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blob_header: ShardBlobHeader = signed_blob_header.message
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```
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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 `blob_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(blob_header.slot) >= get_previous_epoch(state)`
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- _[IGNORE]_ The header is the first header with valid signature received for the `(block_header.proposer_index, blob_header.slot, blob_header.shard)` combination.
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- _[REJECT]_ The `shard` MUST have a committee at the `slot` --
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i.e. validate that `compute_committee_index_from_shard(state, blob_header.slot, blob_header.shard)` doesn't raise an error
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- _[REJECT]_ The proposer signature, `signed_shard_block_header.signature`, is valid with respect to the `block_header.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_reference_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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