135 lines
5.1 KiB
Markdown
135 lines
5.1 KiB
Markdown
# EIP-4844 -- Honest Validator
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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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- [Prerequisites](#prerequisites)
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- [Helpers](#helpers)
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- [`is_data_available`](#is_data_available)
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- [`verify_blobs_sidecar`](#verify_blobs_sidecar)
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- [Beacon chain responsibilities](#beacon-chain-responsibilities)
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- [Block proposal](#block-proposal)
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- [Constructing the `BeaconBlockBody`](#constructing-the-beaconblockbody)
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- [Blob commitments](#blob-commitments)
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- [Beacon Block publishing time](#beacon-block-publishing-time)
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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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This document represents the changes to be made in the code of an "honest validator" to implement EIP-4844.
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## Prerequisites
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This document is an extension of the [Bellatrix -- Honest Validator](../bellatrix/validator.md) guide.
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All behaviors and definitions defined in this document, and documents it extends, carry over unless explicitly noted or overridden.
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All terminology, constants, functions, and protocol mechanics defined in the updated [Beacon Chain doc of EIP4844](./beacon-chain.md) are requisite for this document and used throughout.
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Please see related Beacon Chain doc before continuing and use them as a reference throughout.
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## Helpers
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### `is_data_available`
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The implementation of `is_data_available` is meant to change with later sharding upgrades.
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Initially, it requires every verifying actor to retrieve the matching `BlobsSidecar`,
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and verify the sidecar with `verify_blobs`.
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Without the sidecar the block may be processed further optimistically,
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but MUST NOT be considered valid until a valid `BlobsSidecar` has been downloaded.
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```python
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def is_data_available(slot: Slot, beacon_block_root: Root, kzgs: Sequence[KZGCommitment]):
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sidecar = retrieve_blobs_sidecar(slot, beacon_block_root) # implementation dependent, raises an exception if not available
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verify_blobs_sidecar(slot, beacon_block_root, kzgs, sidecar)
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```
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### `verify_blobs_sidecar`
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```python
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def verify_blobs_sidecar(slot: Slot, beacon_block_root: Root,
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expected_kzgs: Sequence[KZGCommitment], blobs_sidecar: BlobsSidecar):
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assert slot == blobs_sidecar.beacon_block_slot
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assert beacon_block_root == blobs_sidecar.beacon_block_root
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blobs = blobs_sidecar.blobs
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assert len(expected_kzgs) == len(blobs)
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for kzg, blob in zip(expected_kzgs, blobs):
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assert blob_to_kzg(blob) == kzg
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```
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## Beacon chain responsibilities
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All validator responsibilities remain unchanged other than those noted below.
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Namely, the blob handling and the addition of `BlobsSidecar`.
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### Block proposal
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#### Constructing the `BeaconBlockBody`
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##### Blob commitments
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After retrieving the execution payload from the execution engine as specified in Bellatrix,
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the blobs are retrieved and processed:
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```python
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# execution_payload = execution_engine.get_payload(payload_id)
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# block.body.execution_payload = execution_payload
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# ...
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kzgs, blobs = get_blobs(payload_id)
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# Optionally sanity-check that the KZG commitments match the versioned hashes in the transactions
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assert verify_kzgs_against_transactions(execution_payload.transactions, kzgs)
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# Optionally sanity-check that the KZG commitments match the blobs (as produced by the execution engine)
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assert len(kzgs) == len(blobs) and [blob_to_kzg(blob) == kzg for blob, kzg in zip(blobs, kzgs)]
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# Update the block body
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block.body.blob_kzgs = kzgs
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```
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The `blobs` should be held with the block in preparation of publishing.
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Without the `blobs`, the published block will effectively be ignored by honest validators.
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Note: This API is *unstable*. `get_blobs` and `get_payload` may be unified.
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Implementers may also retrieve blobs individually per transaction.
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### Beacon Block publishing time
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Before publishing a prepared beacon block proposal, the corresponding blobs are packaged into a sidecar object for distribution to the network:
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```python
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blobs_sidecar = BlobsSidecar(
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beacon_block_root=hash_tree_root(beacon_block)
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beacon_block_slot=beacon_block.slot
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shard=0,
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blobs=blobs,
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)
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```
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And then signed:
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```python
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domain = get_domain(state, DOMAIN_BLOBS_SIDECAR, blobs_sidecar.beacon_block_slot / SLOTS_PER_EPOCH)
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signing_root = compute_signing_root(blobs_sidecar, domain)
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signature = bls.Sign(privkey, signing_root)
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signed_blobs_sidecar = SignedBlobsSidecar(message=blobs_sidecar, signature=signature)
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```
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This `signed_blobs_sidecar` is then published to the global `blobs_sidecar` topic as soon as the `beacon_block` is published.
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After publishing the sidecar peers on the network may request the sidecar through sync-requests, or a local user may be interested.
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The validator MUST hold on to blobs for `MIN_EPOCHS_FOR_BLOBS_SIDECARS_REQUESTS` epochs and serve when capable,
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to ensure the data-availability of these blobs throughout the network.
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After `MIN_EPOCHS_FOR_BLOBS_SIDECARS_REQUESTS` nodes MAY prune the blobs and/or stop serving them.
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