750 lines
31 KiB
Markdown
750 lines
31 KiB
Markdown
# Ethereum 2.0 Altair Beacon chain changes
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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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- [Custom types](#custom-types)
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- [Constants](#constants)
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- [Participation flag indices](#participation-flag-indices)
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- [Incentivization weights](#incentivization-weights)
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- [Domain types](#domain-types)
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- [Misc](#misc)
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- [Preset](#preset)
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- [Updated penalty values](#updated-penalty-values)
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- [Sync committee](#sync-committee)
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- [Configuration](#configuration)
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- [Inactivity penalties](#inactivity-penalties)
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- [Containers](#containers)
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- [Modified containers](#modified-containers)
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- [`BeaconBlockBody`](#beaconblockbody)
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- [`BeaconState`](#beaconstate)
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- [New containers](#new-containers)
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- [`SyncAggregate`](#syncaggregate)
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- [`SyncCommittee`](#synccommittee)
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- [Helper functions](#helper-functions)
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- [`Predicates`](#predicates)
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- [`eth2_fast_aggregate_verify`](#eth2_fast_aggregate_verify)
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- [Misc](#misc-1)
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- [`add_flag`](#add_flag)
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- [`has_flag`](#has_flag)
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- [Beacon state accessors](#beacon-state-accessors)
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- [`get_next_sync_committee_indices`](#get_next_sync_committee_indices)
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- [`get_next_sync_committee`](#get_next_sync_committee)
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- [`get_base_reward_per_increment`](#get_base_reward_per_increment)
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- [`get_base_reward`](#get_base_reward)
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- [`get_unslashed_participating_indices`](#get_unslashed_participating_indices)
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- [`get_attestation_participation_flag_indices`](#get_attestation_participation_flag_indices)
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- [`get_flag_index_deltas`](#get_flag_index_deltas)
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- [Modified `get_inactivity_penalty_deltas`](#modified-get_inactivity_penalty_deltas)
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- [Beacon state mutators](#beacon-state-mutators)
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- [Modified `slash_validator`](#modified-slash_validator)
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- [Block processing](#block-processing)
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- [Modified `process_attestation`](#modified-process_attestation)
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- [Modified `process_deposit`](#modified-process_deposit)
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- [Sync committee processing](#sync-committee-processing)
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- [Epoch processing](#epoch-processing)
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- [Justification and finalization](#justification-and-finalization)
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- [Inactivity scores](#inactivity-scores)
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- [Rewards and penalties](#rewards-and-penalties)
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- [Slashings](#slashings)
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- [Participation flags updates](#participation-flags-updates)
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- [Sync committee updates](#sync-committee-updates)
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- [Initialize state for pure Altair testnets and test vectors](#initialize-state-for-pure-altair-testnets-and-test-vectors)
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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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Altair is the first beacon chain hard fork. Its main features are:
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* sync committees to support light clients
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* incentive accounting reforms to reduce spec complexity
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* penalty parameter updates towards their planned maximally punitive values
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## Custom types
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| Name | SSZ equivalent | Description |
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| - | - | - |
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| `ParticipationFlags` | `uint8` | a succinct representation of 8 boolean participation flags |
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## Constants
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### Participation flag indices
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| Name | Value |
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| - | - |
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| `TIMELY_SOURCE_FLAG_INDEX` | `0` |
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| `TIMELY_TARGET_FLAG_INDEX` | `1` |
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| `TIMELY_HEAD_FLAG_INDEX` | `2` |
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### Incentivization weights
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| Name | Value |
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| - | - |
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| `TIMELY_SOURCE_WEIGHT` | `uint64(12)` |
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| `TIMELY_TARGET_WEIGHT` | `uint64(24)` |
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| `TIMELY_HEAD_WEIGHT` | `uint64(12)` |
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| `SYNC_REWARD_WEIGHT` | `uint64(8)` |
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| `PROPOSER_WEIGHT` | `uint64(8)` |
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| `WEIGHT_DENOMINATOR` | `uint64(64)` |
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*Note*: The sum of the weights equal `WEIGHT_DENOMINATOR`.
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### Domain types
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| Name | Value |
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| - | - |
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| `DOMAIN_SYNC_COMMITTEE` | `DomainType('0x07000000')` |
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| `DOMAIN_SYNC_COMMITTEE_SELECTION_PROOF` | `DomainType('0x08000000')` |
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| `DOMAIN_CONTRIBUTION_AND_PROOF` | `DomainType('0x09000000')` |
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### Misc
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| Name | Value |
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| - | - |
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| `G2_POINT_AT_INFINITY` | `BLSSignature(b'\xc0' + b'\x00' * 95)` |
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| `PARTICIPATION_FLAG_WEIGHTS` | `[TIMELY_SOURCE_WEIGHT, TIMELY_TARGET_WEIGHT, TIMELY_HEAD_WEIGHT]` |
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## Preset
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### Updated penalty values
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This patch updates a few configuration values to move penalty parameters closer to their final, maximum security values.
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*Note*: The spec does *not* override previous configuration values but instead creates new values and replaces usage throughout.
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| Name | Value |
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| - | - |
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| `INACTIVITY_PENALTY_QUOTIENT_ALTAIR` | `uint64(3 * 2**24)` (= 50,331,648) |
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| `MIN_SLASHING_PENALTY_QUOTIENT_ALTAIR` | `uint64(2**6)` (= 64) |
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| `PROPORTIONAL_SLASHING_MULTIPLIER_ALTAIR` | `uint64(2)` |
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### Sync committee
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| Name | Value | Unit | Duration |
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| - | - | - | - |
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| `SYNC_COMMITTEE_SIZE` | `uint64(2**9)` (= 512) | Validators | |
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| `EPOCHS_PER_SYNC_COMMITTEE_PERIOD` | `uint64(2**9)` (= 512) | epochs | ~54 hours |
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## Configuration
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### Inactivity penalties
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| Name | Value | Description |
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| - | - | - |
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| `INACTIVITY_SCORE_BIAS` | `uint64(4)` | score points per inactive epoch |
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| `INACTIVITY_SCORE_RECOVERY_RATE` | `uint64(16)` | score points per recovering epoch |
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## Containers
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### Modified containers
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#### `BeaconBlockBody`
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```python
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class BeaconBlockBody(Container):
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randao_reveal: BLSSignature
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eth1_data: Eth1Data # Eth1 data vote
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graffiti: Bytes32 # Arbitrary data
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# Operations
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proposer_slashings: List[ProposerSlashing, MAX_PROPOSER_SLASHINGS]
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attester_slashings: List[AttesterSlashing, MAX_ATTESTER_SLASHINGS]
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attestations: List[Attestation, MAX_ATTESTATIONS]
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deposits: List[Deposit, MAX_DEPOSITS]
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voluntary_exits: List[SignedVoluntaryExit, MAX_VOLUNTARY_EXITS]
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# [New in Altair]
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sync_aggregate: SyncAggregate
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```
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#### `BeaconState`
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```python
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class BeaconState(Container):
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# Versioning
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genesis_time: uint64
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genesis_validators_root: Root
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slot: Slot
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fork: Fork
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# History
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latest_block_header: BeaconBlockHeader
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block_roots: Vector[Root, SLOTS_PER_HISTORICAL_ROOT]
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state_roots: Vector[Root, SLOTS_PER_HISTORICAL_ROOT]
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historical_roots: List[Root, HISTORICAL_ROOTS_LIMIT]
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# Eth1
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eth1_data: Eth1Data
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eth1_data_votes: List[Eth1Data, EPOCHS_PER_ETH1_VOTING_PERIOD * SLOTS_PER_EPOCH]
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eth1_deposit_index: uint64
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# Registry
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validators: List[Validator, VALIDATOR_REGISTRY_LIMIT]
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balances: List[Gwei, VALIDATOR_REGISTRY_LIMIT]
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# Randomness
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randao_mixes: Vector[Bytes32, EPOCHS_PER_HISTORICAL_VECTOR]
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# Slashings
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slashings: Vector[Gwei, EPOCHS_PER_SLASHINGS_VECTOR] # Per-epoch sums of slashed effective balances
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# Participation
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previous_epoch_participation: List[ParticipationFlags, VALIDATOR_REGISTRY_LIMIT] # [Modified in Altair]
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current_epoch_participation: List[ParticipationFlags, VALIDATOR_REGISTRY_LIMIT] # [Modified in Altair]
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# Finality
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justification_bits: Bitvector[JUSTIFICATION_BITS_LENGTH] # Bit set for every recent justified epoch
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previous_justified_checkpoint: Checkpoint
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current_justified_checkpoint: Checkpoint
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finalized_checkpoint: Checkpoint
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# Inactivity
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inactivity_scores: List[uint64, VALIDATOR_REGISTRY_LIMIT] # [New in Altair]
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# Sync
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current_sync_committee: SyncCommittee # [New in Altair]
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next_sync_committee: SyncCommittee # [New in Altair]
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```
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### New containers
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#### `SyncAggregate`
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```python
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class SyncAggregate(Container):
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sync_committee_bits: Bitvector[SYNC_COMMITTEE_SIZE]
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sync_committee_signature: BLSSignature
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```
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#### `SyncCommittee`
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```python
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class SyncCommittee(Container):
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pubkeys: Vector[BLSPubkey, SYNC_COMMITTEE_SIZE]
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aggregate_pubkey: BLSPubkey
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```
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## Helper functions
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### `Predicates`
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#### `eth2_fast_aggregate_verify`
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```python
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def eth2_fast_aggregate_verify(pubkeys: Sequence[BLSPubkey], message: Bytes32, signature: BLSSignature) -> bool:
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"""
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Wrapper to ``bls.FastAggregateVerify`` accepting the ``G2_POINT_AT_INFINITY`` signature when ``pubkeys`` is empty.
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"""
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if len(pubkeys) == 0 and signature == G2_POINT_AT_INFINITY:
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return True
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return bls.FastAggregateVerify(pubkeys, message, signature)
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```
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### Misc
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#### `add_flag`
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```python
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def add_flag(flags: ParticipationFlags, flag_index: int) -> ParticipationFlags:
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"""
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Return a new ``ParticipationFlags`` adding ``flag_index`` to ``flags``.
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"""
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flag = ParticipationFlags(2**flag_index)
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return flags | flag
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```
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#### `has_flag`
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```python
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def has_flag(flags: ParticipationFlags, flag_index: int) -> bool:
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"""
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Return whether ``flags`` has ``flag_index`` set.
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"""
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flag = ParticipationFlags(2**flag_index)
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return flags & flag == flag
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```
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### Beacon state accessors
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#### `get_next_sync_committee_indices`
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```python
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def get_next_sync_committee_indices(state: BeaconState) -> Sequence[ValidatorIndex]:
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"""
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Return the sequence of sync committee indices (which may include duplicate indices)
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for the next sync committee, given a ``state`` at a sync committee period boundary.
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Note: Committee can contain duplicate indices for small validator sets (< SYNC_COMMITTEE_SIZE + 128)
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"""
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epoch = Epoch(get_current_epoch(state) + 1)
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MAX_RANDOM_BYTE = 2**8 - 1
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active_validator_indices = get_active_validator_indices(state, epoch)
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active_validator_count = uint64(len(active_validator_indices))
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seed = get_seed(state, epoch, DOMAIN_SYNC_COMMITTEE)
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i = 0
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sync_committee_indices: List[ValidatorIndex] = []
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while len(sync_committee_indices) < SYNC_COMMITTEE_SIZE:
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shuffled_index = compute_shuffled_index(uint64(i % active_validator_count), active_validator_count, seed)
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candidate_index = active_validator_indices[shuffled_index]
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random_byte = hash(seed + uint_to_bytes(uint64(i // 32)))[i % 32]
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effective_balance = state.validators[candidate_index].effective_balance
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if effective_balance * MAX_RANDOM_BYTE >= MAX_EFFECTIVE_BALANCE * random_byte:
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sync_committee_indices.append(candidate_index)
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i += 1
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return sync_committee_indices
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```
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#### `get_next_sync_committee`
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```python
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def get_next_sync_committee(state: BeaconState) -> SyncCommittee:
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"""
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Return the *next* sync committee for a given ``state``.
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``SyncCommittee`` contains an aggregate pubkey that enables
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resource-constrained clients to save some computation when verifying
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the sync committee's signature.
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``SyncCommittee`` can also contain duplicate pubkeys, when ``get_next_sync_committee_indices``
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returns duplicate indices. Implementations must take care when handling
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optimizations relating to aggregation and verification in the presence of duplicates.
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Note: This function should only be called at sync committee period boundaries by ``process_sync_committee_updates``
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as ``get_next_sync_committee_indices`` is not stable within a given period.
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"""
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indices = get_next_sync_committee_indices(state)
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pubkeys = [state.validators[index].pubkey for index in indices]
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aggregate_pubkey = bls.AggregatePKs(pubkeys)
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return SyncCommittee(pubkeys=pubkeys, aggregate_pubkey=aggregate_pubkey)
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```
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#### `get_base_reward_per_increment`
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```python
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def get_base_reward_per_increment(state: BeaconState) -> Gwei:
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return Gwei(EFFECTIVE_BALANCE_INCREMENT * BASE_REWARD_FACTOR // integer_squareroot(get_total_active_balance(state)))
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```
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#### `get_base_reward`
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*Note*: The function `get_base_reward` is modified with the removal of `BASE_REWARDS_PER_EPOCH` and the use of increment based accounting.
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```python
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def get_base_reward(state: BeaconState, index: ValidatorIndex) -> Gwei:
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"""
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Return the base reward for the validator defined by ``index`` with respect to the current ``state``.
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Note: An optimally performing validator can earn one base reward per epoch over a long time horizon.
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This takes into account both per-epoch (e.g. attestation) and intermittent duties (e.g. block proposal
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and sync committees).
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"""
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increments = state.validators[index].effective_balance // EFFECTIVE_BALANCE_INCREMENT
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return Gwei(increments * get_base_reward_per_increment(state))
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```
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#### `get_unslashed_participating_indices`
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```python
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def get_unslashed_participating_indices(state: BeaconState, flag_index: int, epoch: Epoch) -> Set[ValidatorIndex]:
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"""
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Return the set of validator indices that are both active and unslashed for the given ``flag_index`` and ``epoch``.
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"""
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assert epoch in (get_previous_epoch(state), get_current_epoch(state))
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if epoch == get_current_epoch(state):
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epoch_participation = state.current_epoch_participation
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else:
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epoch_participation = state.previous_epoch_participation
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active_validator_indices = get_active_validator_indices(state, epoch)
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participating_indices = [i for i in active_validator_indices if has_flag(epoch_participation[i], flag_index)]
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return set(filter(lambda index: not state.validators[index].slashed, participating_indices))
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```
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#### `get_attestation_participation_flag_indices`
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```python
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def get_attestation_participation_flag_indices(state: BeaconState,
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data: AttestationData,
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inclusion_delay: uint64) -> Sequence[int]:
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"""
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Return the flag indices that are satisfied by an attestation.
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"""
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if data.target.epoch == get_current_epoch(state):
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justified_checkpoint = state.current_justified_checkpoint
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else:
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justified_checkpoint = state.previous_justified_checkpoint
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# Matching roots
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is_matching_source = data.source == justified_checkpoint
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is_matching_target = is_matching_source and data.target.root == get_block_root(state, data.target.epoch)
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is_matching_head = is_matching_target and data.beacon_block_root == get_block_root_at_slot(state, data.slot)
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assert is_matching_source
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participation_flag_indices = []
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if is_matching_source and inclusion_delay <= integer_squareroot(SLOTS_PER_EPOCH):
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participation_flag_indices.append(TIMELY_SOURCE_FLAG_INDEX)
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if is_matching_target and inclusion_delay <= SLOTS_PER_EPOCH:
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participation_flag_indices.append(TIMELY_TARGET_FLAG_INDEX)
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if is_matching_head and inclusion_delay == MIN_ATTESTATION_INCLUSION_DELAY:
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participation_flag_indices.append(TIMELY_HEAD_FLAG_INDEX)
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return participation_flag_indices
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```
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#### `get_flag_index_deltas`
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```python
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def get_flag_index_deltas(state: BeaconState, flag_index: int) -> Tuple[Sequence[Gwei], Sequence[Gwei]]:
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"""
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Return the deltas for a given ``flag_index`` by scanning through the participation flags.
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"""
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rewards = [Gwei(0)] * len(state.validators)
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penalties = [Gwei(0)] * len(state.validators)
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previous_epoch = get_previous_epoch(state)
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unslashed_participating_indices = get_unslashed_participating_indices(state, flag_index, previous_epoch)
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weight = PARTICIPATION_FLAG_WEIGHTS[flag_index]
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unslashed_participating_balance = get_total_balance(state, unslashed_participating_indices)
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unslashed_participating_increments = unslashed_participating_balance // EFFECTIVE_BALANCE_INCREMENT
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active_increments = get_total_active_balance(state) // EFFECTIVE_BALANCE_INCREMENT
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for index in get_eligible_validator_indices(state):
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base_reward = get_base_reward(state, index)
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if index in unslashed_participating_indices:
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if not is_in_inactivity_leak(state):
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reward_numerator = base_reward * weight * unslashed_participating_increments
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rewards[index] += Gwei(reward_numerator // (active_increments * WEIGHT_DENOMINATOR))
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elif flag_index != TIMELY_HEAD_FLAG_INDEX:
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penalties[index] += Gwei(base_reward * weight // WEIGHT_DENOMINATOR)
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return rewards, penalties
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```
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#### Modified `get_inactivity_penalty_deltas`
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```python
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def get_inactivity_penalty_deltas(state: BeaconState) -> Tuple[Sequence[Gwei], Sequence[Gwei]]:
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"""
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Return the inactivity penalty deltas by considering timely target participation flags and inactivity scores.
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"""
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rewards = [Gwei(0) for _ in range(len(state.validators))]
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penalties = [Gwei(0) for _ in range(len(state.validators))]
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previous_epoch = get_previous_epoch(state)
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matching_target_indices = get_unslashed_participating_indices(state, TIMELY_TARGET_FLAG_INDEX, previous_epoch)
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for index in get_eligible_validator_indices(state):
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if index not in matching_target_indices:
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penalty_numerator = state.validators[index].effective_balance * state.inactivity_scores[index]
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penalty_denominator = INACTIVITY_SCORE_BIAS * INACTIVITY_PENALTY_QUOTIENT_ALTAIR
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penalties[index] += Gwei(penalty_numerator // penalty_denominator)
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return rewards, penalties
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```
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### Beacon state mutators
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#### Modified `slash_validator`
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*Note*: The function `slash_validator` is modified to use `MIN_SLASHING_PENALTY_QUOTIENT_ALTAIR`
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and use `PROPOSER_WEIGHT` when calculating the proposer reward.
|
|
|
|
```python
|
|
def slash_validator(state: BeaconState,
|
|
slashed_index: ValidatorIndex,
|
|
whistleblower_index: ValidatorIndex=None) -> None:
|
|
"""
|
|
Slash the validator with index ``slashed_index``.
|
|
"""
|
|
epoch = get_current_epoch(state)
|
|
initiate_validator_exit(state, slashed_index)
|
|
validator = state.validators[slashed_index]
|
|
validator.slashed = True
|
|
validator.withdrawable_epoch = max(validator.withdrawable_epoch, Epoch(epoch + EPOCHS_PER_SLASHINGS_VECTOR))
|
|
state.slashings[epoch % EPOCHS_PER_SLASHINGS_VECTOR] += validator.effective_balance
|
|
decrease_balance(state, slashed_index, validator.effective_balance // MIN_SLASHING_PENALTY_QUOTIENT_ALTAIR)
|
|
|
|
# Apply proposer and whistleblower rewards
|
|
proposer_index = get_beacon_proposer_index(state)
|
|
if whistleblower_index is None:
|
|
whistleblower_index = proposer_index
|
|
whistleblower_reward = Gwei(validator.effective_balance // WHISTLEBLOWER_REWARD_QUOTIENT)
|
|
proposer_reward = Gwei(whistleblower_reward * PROPOSER_WEIGHT // WEIGHT_DENOMINATOR)
|
|
increase_balance(state, proposer_index, proposer_reward)
|
|
increase_balance(state, whistleblower_index, Gwei(whistleblower_reward - proposer_reward))
|
|
```
|
|
|
|
### Block processing
|
|
|
|
```python
|
|
def process_block(state: BeaconState, block: BeaconBlock) -> None:
|
|
process_block_header(state, block)
|
|
process_randao(state, block.body)
|
|
process_eth1_data(state, block.body)
|
|
process_operations(state, block.body) # [Modified in Altair]
|
|
process_sync_committee(state, block.body.sync_aggregate) # [New in Altair]
|
|
```
|
|
|
|
#### Modified `process_attestation`
|
|
|
|
*Note*: The function `process_attestation` is modified to do incentive accounting with epoch participation flags.
|
|
|
|
```python
|
|
def process_attestation(state: BeaconState, attestation: Attestation) -> None:
|
|
data = attestation.data
|
|
assert data.target.epoch in (get_previous_epoch(state), get_current_epoch(state))
|
|
assert data.target.epoch == compute_epoch_at_slot(data.slot)
|
|
assert data.slot + MIN_ATTESTATION_INCLUSION_DELAY <= state.slot <= data.slot + SLOTS_PER_EPOCH
|
|
assert data.index < get_committee_count_per_slot(state, data.target.epoch)
|
|
|
|
committee = get_beacon_committee(state, data.slot, data.index)
|
|
assert len(attestation.aggregation_bits) == len(committee)
|
|
|
|
# Participation flag indices
|
|
participation_flag_indices = get_attestation_participation_flag_indices(state, data, state.slot - data.slot)
|
|
|
|
# Verify signature
|
|
assert is_valid_indexed_attestation(state, get_indexed_attestation(state, attestation))
|
|
|
|
# Update epoch participation flags
|
|
if data.target.epoch == get_current_epoch(state):
|
|
epoch_participation = state.current_epoch_participation
|
|
else:
|
|
epoch_participation = state.previous_epoch_participation
|
|
|
|
proposer_reward_numerator = 0
|
|
for index in get_attesting_indices(state, data, attestation.aggregation_bits):
|
|
for flag_index, weight in enumerate(PARTICIPATION_FLAG_WEIGHTS):
|
|
if flag_index in participation_flag_indices and not has_flag(epoch_participation[index], flag_index):
|
|
epoch_participation[index] = add_flag(epoch_participation[index], flag_index)
|
|
proposer_reward_numerator += get_base_reward(state, index) * weight
|
|
|
|
# Reward proposer
|
|
proposer_reward_denominator = (WEIGHT_DENOMINATOR - PROPOSER_WEIGHT) * WEIGHT_DENOMINATOR // PROPOSER_WEIGHT
|
|
proposer_reward = Gwei(proposer_reward_numerator // proposer_reward_denominator)
|
|
increase_balance(state, get_beacon_proposer_index(state), proposer_reward)
|
|
```
|
|
|
|
#### Modified `process_deposit`
|
|
|
|
*Note*: The function `process_deposit` is modified to initialize `inactivity_scores`, `previous_epoch_participation`, and `current_epoch_participation`.
|
|
|
|
```python
|
|
def process_deposit(state: BeaconState, deposit: Deposit) -> None:
|
|
# Verify the Merkle branch
|
|
assert is_valid_merkle_branch(
|
|
leaf=hash_tree_root(deposit.data),
|
|
branch=deposit.proof,
|
|
depth=DEPOSIT_CONTRACT_TREE_DEPTH + 1, # Add 1 for the List length mix-in
|
|
index=state.eth1_deposit_index,
|
|
root=state.eth1_data.deposit_root,
|
|
)
|
|
|
|
# Deposits must be processed in order
|
|
state.eth1_deposit_index += 1
|
|
|
|
pubkey = deposit.data.pubkey
|
|
amount = deposit.data.amount
|
|
validator_pubkeys = [validator.pubkey for validator in state.validators]
|
|
if pubkey not in validator_pubkeys:
|
|
# Verify the deposit signature (proof of possession) which is not checked by the deposit contract
|
|
deposit_message = DepositMessage(
|
|
pubkey=deposit.data.pubkey,
|
|
withdrawal_credentials=deposit.data.withdrawal_credentials,
|
|
amount=deposit.data.amount,
|
|
)
|
|
domain = compute_domain(DOMAIN_DEPOSIT) # Fork-agnostic domain since deposits are valid across forks
|
|
signing_root = compute_signing_root(deposit_message, domain)
|
|
# Initialize validator if the deposit signature is valid
|
|
if bls.Verify(pubkey, signing_root, deposit.data.signature):
|
|
state.validators.append(get_validator_from_deposit(state, deposit))
|
|
state.balances.append(amount)
|
|
state.previous_epoch_participation.append(ParticipationFlags(0b0000_0000))
|
|
state.current_epoch_participation.append(ParticipationFlags(0b0000_0000))
|
|
state.inactivity_scores.append(uint64(0))
|
|
else:
|
|
# Increase balance by deposit amount
|
|
index = ValidatorIndex(validator_pubkeys.index(pubkey))
|
|
increase_balance(state, index, amount)
|
|
```
|
|
|
|
#### Sync committee processing
|
|
|
|
```python
|
|
def process_sync_committee(state: BeaconState, aggregate: SyncAggregate) -> None:
|
|
# Verify sync committee aggregate signature signing over the previous slot block root
|
|
committee_pubkeys = state.current_sync_committee.pubkeys
|
|
participant_pubkeys = [pubkey for pubkey, bit in zip(committee_pubkeys, aggregate.sync_committee_bits) if bit]
|
|
previous_slot = max(state.slot, Slot(1)) - Slot(1)
|
|
domain = get_domain(state, DOMAIN_SYNC_COMMITTEE, compute_epoch_at_slot(previous_slot))
|
|
signing_root = compute_signing_root(get_block_root_at_slot(state, previous_slot), domain)
|
|
assert eth2_fast_aggregate_verify(participant_pubkeys, signing_root, aggregate.sync_committee_signature)
|
|
|
|
# Compute participant and proposer rewards
|
|
total_active_increments = get_total_active_balance(state) // EFFECTIVE_BALANCE_INCREMENT
|
|
total_base_rewards = Gwei(get_base_reward_per_increment(state) * total_active_increments)
|
|
max_participant_rewards = Gwei(total_base_rewards * SYNC_REWARD_WEIGHT // WEIGHT_DENOMINATOR // SLOTS_PER_EPOCH)
|
|
participant_reward = Gwei(max_participant_rewards // SYNC_COMMITTEE_SIZE)
|
|
proposer_reward = Gwei(participant_reward * PROPOSER_WEIGHT // (WEIGHT_DENOMINATOR - PROPOSER_WEIGHT))
|
|
|
|
# Apply participant and proposer rewards
|
|
all_pubkeys = [v.pubkey for v in state.validators]
|
|
committee_indices = [ValidatorIndex(all_pubkeys.index(pubkey)) for pubkey in state.current_sync_committee.pubkeys]
|
|
participant_indices = [index for index, bit in zip(committee_indices, aggregate.sync_committee_bits) if bit]
|
|
for participant_index in participant_indices:
|
|
increase_balance(state, participant_index, participant_reward)
|
|
increase_balance(state, get_beacon_proposer_index(state), proposer_reward)
|
|
```
|
|
|
|
### Epoch processing
|
|
|
|
```python
|
|
def process_epoch(state: BeaconState) -> None:
|
|
process_justification_and_finalization(state) # [Modified in Altair]
|
|
process_inactivity_updates(state) # [New in Altair]
|
|
process_rewards_and_penalties(state) # [Modified in Altair]
|
|
process_registry_updates(state)
|
|
process_slashings(state) # [Modified in Altair]
|
|
process_eth1_data_reset(state)
|
|
process_effective_balance_updates(state)
|
|
process_slashings_reset(state)
|
|
process_randao_mixes_reset(state)
|
|
process_historical_roots_update(state)
|
|
process_participation_flag_updates(state) # [New in Altair]
|
|
process_sync_committee_updates(state) # [New in Altair]
|
|
```
|
|
|
|
#### Justification and finalization
|
|
|
|
*Note*: The function `process_justification_and_finalization` is modified to adapt to the new participation records.
|
|
|
|
```python
|
|
def process_justification_and_finalization(state: BeaconState) -> None:
|
|
# Initial FFG checkpoint values have a `0x00` stub for `root`.
|
|
# Skip FFG updates in the first two epochs to avoid corner cases that might result in modifying this stub.
|
|
if get_current_epoch(state) <= GENESIS_EPOCH + 1:
|
|
return
|
|
previous_indices = get_unslashed_participating_indices(state, TIMELY_TARGET_FLAG_INDEX, get_previous_epoch(state))
|
|
current_indices = get_unslashed_participating_indices(state, TIMELY_TARGET_FLAG_INDEX, get_current_epoch(state))
|
|
total_active_balance = get_total_active_balance(state)
|
|
previous_target_balance = get_total_balance(state, previous_indices)
|
|
current_target_balance = get_total_balance(state, current_indices)
|
|
weigh_justification_and_finalization(state, total_active_balance, previous_target_balance, current_target_balance)
|
|
```
|
|
|
|
#### Inactivity scores
|
|
|
|
*Note*: The function `process_inactivity_updates` is new.
|
|
|
|
```python
|
|
def process_inactivity_updates(state: BeaconState) -> None:
|
|
# Score updates based on previous epoch participation, skip genesis epoch
|
|
if get_current_epoch(state) == GENESIS_EPOCH:
|
|
return
|
|
|
|
for index in get_eligible_validator_indices(state):
|
|
# Increase inactivity score of inactive validators
|
|
if index in get_unslashed_participating_indices(state, TIMELY_TARGET_FLAG_INDEX, get_previous_epoch(state)):
|
|
state.inactivity_scores[index] -= min(1, state.inactivity_scores[index])
|
|
else:
|
|
state.inactivity_scores[index] += INACTIVITY_SCORE_BIAS
|
|
# Decrease the score of all validators for forgiveness when not during a leak
|
|
if not is_in_inactivity_leak(state):
|
|
state.inactivity_scores[index] -= min(INACTIVITY_SCORE_RECOVERY_RATE, state.inactivity_scores[index])
|
|
```
|
|
|
|
#### Rewards and penalties
|
|
|
|
*Note*: The function `process_rewards_and_penalties` is modified to support the incentive accounting reforms.
|
|
|
|
```python
|
|
def process_rewards_and_penalties(state: BeaconState) -> None:
|
|
# No rewards are applied at the end of `GENESIS_EPOCH` because rewards are for work done in the previous epoch
|
|
if get_current_epoch(state) == GENESIS_EPOCH:
|
|
return
|
|
|
|
flag_deltas = [get_flag_index_deltas(state, flag_index) for flag_index in range(len(PARTICIPATION_FLAG_WEIGHTS))]
|
|
deltas = flag_deltas + [get_inactivity_penalty_deltas(state)]
|
|
for (rewards, penalties) in deltas:
|
|
for index in range(len(state.validators)):
|
|
increase_balance(state, ValidatorIndex(index), rewards[index])
|
|
decrease_balance(state, ValidatorIndex(index), penalties[index])
|
|
```
|
|
|
|
#### Slashings
|
|
|
|
*Note*: The function `process_slashings` is modified to use `PROPORTIONAL_SLASHING_MULTIPLIER_ALTAIR`.
|
|
|
|
```python
|
|
def process_slashings(state: BeaconState) -> None:
|
|
epoch = get_current_epoch(state)
|
|
total_balance = get_total_active_balance(state)
|
|
adjusted_total_slashing_balance = min(sum(state.slashings) * PROPORTIONAL_SLASHING_MULTIPLIER_ALTAIR, total_balance)
|
|
for index, validator in enumerate(state.validators):
|
|
if validator.slashed and epoch + EPOCHS_PER_SLASHINGS_VECTOR // 2 == validator.withdrawable_epoch:
|
|
increment = EFFECTIVE_BALANCE_INCREMENT # Factored out from penalty numerator to avoid uint64 overflow
|
|
penalty_numerator = validator.effective_balance // increment * adjusted_total_slashing_balance
|
|
penalty = penalty_numerator // total_balance * increment
|
|
decrease_balance(state, ValidatorIndex(index), penalty)
|
|
```
|
|
|
|
#### Participation flags updates
|
|
|
|
*Note*: The function `process_participation_flag_updates` is new.
|
|
|
|
```python
|
|
def process_participation_flag_updates(state: BeaconState) -> None:
|
|
state.previous_epoch_participation = state.current_epoch_participation
|
|
state.current_epoch_participation = [ParticipationFlags(0b0000_0000) for _ in range(len(state.validators))]
|
|
```
|
|
|
|
#### Sync committee updates
|
|
|
|
*Note*: The function `process_sync_committee_updates` is new.
|
|
|
|
```python
|
|
def process_sync_committee_updates(state: BeaconState) -> None:
|
|
next_epoch = get_current_epoch(state) + Epoch(1)
|
|
if next_epoch % EPOCHS_PER_SYNC_COMMITTEE_PERIOD == 0:
|
|
state.current_sync_committee = state.next_sync_committee
|
|
state.next_sync_committee = get_next_sync_committee(state)
|
|
```
|
|
|
|
## Initialize state for pure Altair testnets and test vectors
|
|
|
|
This helper function is only for initializing the state for pure Altair testnets and tests.
|
|
|
|
*Note*: The function `initialize_beacon_state_from_eth1` is modified: (1) using `ALTAIR_FORK_VERSION` as the current fork version, (2) utilizing the Altair `BeaconBlockBody` when constructing the initial `latest_block_header`, and (3) adding initial sync committees.
|
|
|
|
```python
|
|
def initialize_beacon_state_from_eth1(eth1_block_hash: Bytes32,
|
|
eth1_timestamp: uint64,
|
|
deposits: Sequence[Deposit]) -> BeaconState:
|
|
fork = Fork(
|
|
previous_version=GENESIS_FORK_VERSION,
|
|
current_version=ALTAIR_FORK_VERSION, # [Modified in Altair]
|
|
epoch=GENESIS_EPOCH,
|
|
)
|
|
state = BeaconState(
|
|
genesis_time=eth1_timestamp + GENESIS_DELAY,
|
|
fork=fork,
|
|
eth1_data=Eth1Data(block_hash=eth1_block_hash, deposit_count=uint64(len(deposits))),
|
|
latest_block_header=BeaconBlockHeader(body_root=hash_tree_root(BeaconBlockBody())),
|
|
randao_mixes=[eth1_block_hash] * EPOCHS_PER_HISTORICAL_VECTOR, # Seed RANDAO with Eth1 entropy
|
|
)
|
|
|
|
# Process deposits
|
|
leaves = list(map(lambda deposit: deposit.data, deposits))
|
|
for index, deposit in enumerate(deposits):
|
|
deposit_data_list = List[DepositData, 2**DEPOSIT_CONTRACT_TREE_DEPTH](*leaves[:index + 1])
|
|
state.eth1_data.deposit_root = hash_tree_root(deposit_data_list)
|
|
process_deposit(state, deposit)
|
|
|
|
# Process activations
|
|
for index, validator in enumerate(state.validators):
|
|
balance = state.balances[index]
|
|
validator.effective_balance = min(balance - balance % EFFECTIVE_BALANCE_INCREMENT, MAX_EFFECTIVE_BALANCE)
|
|
if validator.effective_balance == MAX_EFFECTIVE_BALANCE:
|
|
validator.activation_eligibility_epoch = GENESIS_EPOCH
|
|
validator.activation_epoch = GENESIS_EPOCH
|
|
|
|
# Set genesis validators root for domain separation and chain versioning
|
|
state.genesis_validators_root = hash_tree_root(state.validators)
|
|
|
|
# [New in Altair] Fill in sync committees
|
|
# Note: A duplicate committee is assigned for the current and next committee at genesis
|
|
state.current_sync_committee = get_next_sync_committee(state)
|
|
state.next_sync_committee = get_next_sync_committee(state)
|
|
|
|
return state
|
|
```
|