add light client to phase 1 validator
This commit is contained in:
Danny Ryan
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d789f3d32d
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@ -12,6 +12,7 @@
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- [Custom types](#custom-types)
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- [Configuration](#configuration)
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- [Misc](#misc)
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- [Domain types](#domain-types)
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- [Updated containers](#updated-containers)
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- [Extended `AttestationData`](#extended-attestationdata)
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- [Extended `Attestation`](#extended-attestation)
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@ -30,7 +31,6 @@
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- [`ShardTransition`](#shardtransition)
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- [`CompactCommittee`](#compactcommittee)
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- [`AttestationCustodyBitWrapper`](#attestationcustodybitwrapper)
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- [`LightClientVote`](#lightclientvote)
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- [Helper functions](#helper-functions)
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- [Misc](#misc-1)
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- [`get_previous_slot`](#get_previous_slot)
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@ -105,9 +105,16 @@ Configuration is not namespaced. Instead it is strictly an extension;
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| `MAX_GASPRICE` | `Gwei(2**14)` (= 16,384) | Gwei | |
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| `MIN_GASPRICE` | `Gwei(2**3)` (= 8) | Gwei | |
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| `GASPRICE_ADJUSTMENT_COEFFICIENT` | `2**3` (= 8) | |
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| `DOMAIN_SHARD_PROPOSAL` | `DomainType('0x80000000')` | |
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| `DOMAIN_SHARD_COMMITTEE` | `DomainType('0x81000000')` | |
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| `DOMAIN_LIGHT_CLIENT` | `DomainType('0x82000000')` | |
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### Domain types
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| Name | Value |
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| - | - |
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| `DOMAIN_SHARD_PROPOSAL` | `DomainType('0x80000000')` |
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| `DOMAIN_SHARD_COMMITTEE` | `DomainType('0x81000000')` |
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| `DOMAIN_LIGHT_CLIENT` | `DomainType('0x82000000')` |
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| `DOMAIN_LIGHT_SELECTION_PROOF` | `DomainType('0x83000000')` |
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| `DOMAIN_LIGHT_AGGREGATE_AND_PROOF` | `DomainType('0x84000000')` |
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## Updated containers
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@ -356,16 +363,6 @@ class AttestationCustodyBitWrapper(Container):
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bit: boolean
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```
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### `LightClientVote`
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```python
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class LightClientVote(Container):
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slot: Slot
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block_root: Root
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aggregation_bits: Bitvector[LIGHT_CLIENT_COMMITTEE_SIZE]
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signature: BLSSignature
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```
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## Helper functions
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### Misc
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@ -12,6 +12,7 @@
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- [Introduction](#introduction)
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- [Prerequisites](#prerequisites)
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- [Constants](#constants)
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- [Misc](#misc)
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- [Becoming a validator](#becoming-a-validator)
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- [Beacon chain validator assignments](#beacon-chain-validator-assignments)
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- [Beacon chain responsibilities](#beacon-chain-responsibilities)
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@ -34,6 +35,20 @@
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- [Construct attestation](#construct-attestation)
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- [Custody bits blocks](#custody-bits-blocks)
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- [Signature](#signature)
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- [Light client committee](#light-client-committee)
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- [Preparation](#preparation)
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- [Light clent vote](#light-clent-vote)
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- [Light client vote data](#light-client-vote-data)
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- [`LightClientVoteData`](#lightclientvotedata)
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- [Construct vote](#construct-vote)
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- [`LightClientVote`](#lightclientvote)
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- [Broadcast](#broadcast)
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- [Light client vote aggregation](#light-client-vote-aggregation)
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- [Aggregation selection](#aggregation-selection)
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- [Construct aggregate](#construct-aggregate)
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- [Broadcast aggregate](#broadcast-aggregate)
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- [`LightAggregateAndProof`](#lightaggregateandproof)
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- [`SignedLightAggregateAndProof`](#signedlightaggregateandproof)
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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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@ -54,6 +69,12 @@ All terminology, constants, functions, and protocol mechanics defined in the [Ph
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See constants from [Phase 0 validator guide](../phase0/validator.md#constants).
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### Misc
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| Name | Value | Unit | Duration |
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| - | - | :-: | :-: |
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| `TARGET_LIGHT_CLIENT_AGGREGATORS_PER_SLOT` | `2**2` (= 8) | validators | |
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## Becoming a validator
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Becoming a validator in Phase 1 is unchanged from Phase 0. See the [Phase 0 validator guide](../phase0/validator.md#becoming-a-validator) for details.
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@ -68,6 +89,8 @@ A validator has two primary responsibilities to the beacon chain: [proposing blo
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These responsibilities are largely unchanged from Phase 0, but utilize the updated `SignedBeaconBlock`, `BeaconBlock`, `BeaconBlockBody`, `Attestation`, and `AttestationData` definitions found in Phase 1. Below notes only the additional and modified behavior with respect to Phase 0.
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Phase 1 adds light client committees and associated responsibilities, discussed [below](#light-client-committee).
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### Block proposal
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#### Preparing for a `BeaconBlock`
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@ -120,9 +143,12 @@ def get_successful_shard_transitions(state: BeaconState,
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committee = get_beacon_committee(state, state.slot, committee_index)
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# Loop over all shard transition roots, looking for a winning root
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shard_transition_roots = set([a.data.shard_transition_root for a in attestations])
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shard_transition_roots = set([a.data.shard_transition_root for a in shard_attestations])
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for shard_transition_root in sorted(shard_transition_roots):
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transition_attestations = [a for a in attestations if a.data.shard_transition_root == shard_transition_root]
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transition_attestations = [
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a for a in shard_attestations
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if a.data.shard_transition_root == shard_transition_root
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]
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transition_participants: Set[ValidatorIndex] = set()
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for attestation in transition_attestations:
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participants = get_attesting_indices(state, attestation.data, attestation.aggregation_bits)
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@ -149,10 +175,10 @@ Then:
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* Set `light_client_signature = best_aggregate.signature`
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```python
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def select_best_light_client_aggregate(block: BeaconBlock,
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def get_best_light_client_aggregate(block: BeaconBlock,
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aggregates: Sequence[LightClientVote]) -> LightClientVote:
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viable_aggregates = [
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aggregate in aggregates
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aggregate for aggregate in aggregates
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if aggregate.slot == get_previous_slot(block.slot) and aggregate.beacon_block_root == block.parent_root
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]
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@ -225,7 +251,7 @@ Set `attestation_data.head_shard_root = hash_tree_root(head_shard_block)`.
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Set `shard_transition` to the value returned by `get_shard_transition()`.
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```python
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def get_shard_transition(state: BeaconState, shard: Shard, shard_blocks: Sequence[ShardBlock])
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def get_shard_transition(state: BeaconState, shard: Shard, shard_blocks: Sequence[ShardBlock]) -> ShardTransition:
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latest_shard_slot = get_latest_slot_for_shard(state, shard)
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offset_slots = [Slot(latest_shard_slot + x) for x in SHARD_BLOCK_OFFSETS if latest_shard_slot + x <= state.slot]
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return ShardTransition()
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@ -254,8 +280,170 @@ Set `attestation.signature = attestation_signature` where `attestation_signature
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def get_attestation_signature(state: BeaconState,
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attestation_data: AttestationData,
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custody_bits_blocks,
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privkey: int) -> List[Bitlist[MAX_VALIDATORS_PER_COMMITTEE], MAX_SHARD_BLOCKS_PER_ATTESTATION]:
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privkey: int
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) -> List[Bitlist[MAX_VALIDATORS_PER_COMMITTEE], MAX_SHARD_BLOCKS_PER_ATTESTATION]:
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pass
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```
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### Light client committee
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In addition to the core beacon chain responsibilities, Phase 1 adds an additional role -- the Light Client Committee -- to aid in light client functionality.
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Validators serve on the light client committee for `LIGHT_CLIENT_COMMITTEE_PERIOD` epochs and the assignment to be on a committee is known `LIGHT_CLIENT_COMMITTEE_PERIOD` epochs in advance.
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#### Preparation
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When `get_current_epoch(state) % LIGHT_CLIENT_COMMITTEE_PERIOD == LIGHT_CLIENT_COMMITTEE_PERIOD - LIGHT_CLIENT_PREPARATION_EPOCHS` each validator must check if they are in the next period light client committee by calling `is_in_next_light_client_committee()`.
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If the validator is in the next light client committee, they must join the `light_client_votes` pubsub topic to begin duties at the start of the next period.
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```python
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def is_in_next_light_client_committee(state: BeaconState, index: ValidatorIndex) -> boolean:
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period_start_epoch = get_current_epoch(state) + LIGHT_CLIENT_COMMITTEE_PERIOD % get_current_epoch(state)
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next_committee = get_light_client_committee(state, period_start_epoch)
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return index in next_committee
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```
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#### Light clent vote
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During a period of epochs that the validator is a part of the light client committee (`validator_index in get_light_client_committee(state, epoch)`), the validator creates and broadcasts a `LightClientVote` at each slot.
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A validator should create and broadcast the `light_client_vote` to the `light_client_votes` pubsub topic when either (a) the validator has received a valid block from the expected block proposer for the current `slot` or (b) two-thirds of the `slot` have transpired (`SECONDS_PER_SLOT / 3` seconds after the start of `slot`) -- whichever comes _first_.
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- Let `light_client_committee = get_light_client_committee(state, compute_epoch_at_slot(slot))`
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##### Light client vote data
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First the validator constructs `light_client_vote_data`, a [`LightClientVoteData`](#lightclientvotedata) object.
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* Let `head_block` be the result of running the fork choice during the assigned slot.
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* Set `light_client_vote.slot = slot`.
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* Set `light_client_vote.beacon_block_root = hash_tree_root(head_block)`.
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###### `LightClientVoteData`
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```python
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class LightClientVoteData(Container):
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slot: Slot
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beacon_block_root: Root
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```
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##### Construct vote
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Then the validator constructs `light_client_vote`, a [`LightClientVote`](#lightclientvote) object.
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* Set `light_client_vote.data = light_client_vote_data`.
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* Set `light_client_vote.aggregation_bits` to be a `Bitvector[LIGHT_CLIENT_COMMITTEE_SIZE]`, where the bit of the index of the validator in the `light_client_committee` is set to `0b1` and all other bits are are set to `0b0`.
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* Set `light_client_vote.signature = vote_signature` where `vote_signature` is obtained from:
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```python
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def get_light_client_vote_signature(state: BeaconState,
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light_client_vote_data: LightClientVoteData,
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privkey: int) -> BLSSignature:
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domain = get_domain(state, DOMAIN_LIGHT_CLIENT, compute_epoch_at_slot(light_client_vote_data.slot))
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signing_root = compute_signing_root(light_client_vote_data, domain)
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return bls.Sign(privkey, signing_root)
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```
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###### `LightClientVote`
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```python
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class LightClientVote(Container):
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data: LightClientVoteData
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aggregation_bits: Bitvector[LIGHT_CLIENT_COMMITTEE_SIZE]
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signature: BLSSignature
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```
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##### Broadcast
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Finally, the validator broadcasts `light_client_vote` to the `light_client_votes` pubsub topic.
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#### Light client vote aggregation
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Some validators in the light client committee are selected to locally aggregate light client votes with a similar `light_client_vote_data` to their constructed `light_client_vote` for the assigned `slot`.
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#### Aggregation selection
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A validator is selected to aggregate based upon the return value of `is_light_client_aggregator()`.
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```python
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def get_light_client_slot_signature(state: BeaconState, slot: Slot, privkey: int) -> BLSSignature:
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domain = get_domain(state, DOMAIN_LIGHT_SELECTION_PROOF, compute_epoch_at_slot(slot))
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signing_root = compute_signing_root(slot, domain)
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return bls.Sign(privkey, signing_root)
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```
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```python
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def is_light_client_aggregator(state: BeaconState, slot: Slot, slot_signature: BLSSignature) -> bool:
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committee = get_light_client_committee(state, compute_epoch_at_slot(slot))
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modulo = max(1, len(committee) // TARGET_LIGHT_CLIENT_AGGREGATORS_PER_SLOT)
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return bytes_to_int(hash(slot_signature)[0:8]) % modulo == 0
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```
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#### Construct aggregate
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If the validator is selected to aggregate (`is_light_client_aggregator()`), they construct an aggregate light client vote via the following.
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Collect `light_client_votes` seen via gossip during the `slot` that have an equivalent `light_client_vote_data` to that constructed by the validator, and create a `aggregate_light_client_vote: LightClientVote` with the following fields.
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* Set `aggregate_light_client_vote.data = light_client_vote_data` where `light_client_vote_data` is the `LightClientVoteData` object that is the same for each individual light client vote being aggregated.
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* Set `aggregate_light_client_vote.aggregation_bits` to be a `Bitvector[LIGHT_CLIENT_COMMITTEE_SIZE]`, where each bit set from each individual light client vote is set to `0b1`.
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* Set `aggregate_light_client_vote.signature = aggregate_light_client_signature` where `aggregate_light_client_signature` is obtained from `get_aggregate_light_client_signature`.
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```python
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def get_aggregate_light_client_signature(light_client_votes: Sequence[LightClientVote]) -> BLSSignature:
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signatures = [light_client_vote.signature for light_client_vote in light_client_votes]
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return bls.Aggregate(signatures)
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```
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#### Broadcast aggregate
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If the validator is selected to aggregate (`is_light_client_aggregator`), then they broadcast their best aggregate light client vote as a `SignedLightAggregateAndProof` to the global aggregate light client vote channel (`aggregate_light_client_votes`) two-thirds of the way through the `slot`-that is, `SECONDS_PER_SLOT * 2 / 3` seconds after the start of `slot`.
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Selection proofs are provided in `LightAggregateAndProof` to prove to the gossip channel that the validator has been selected as an aggregator.
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`LightAggregateAndProof` messages are signed by the aggregator and broadcast inside of `SignedLightAggregateAndProof` objects to prevent a class of DoS attacks and message forgeries.
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First, `light_aggregate_and_proof = get_light_aggregate_and_proof(state, validator_index, aggregate_light_client_vote, privkey)` is constructed.
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```python
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def get_light_aggregate_and_proof(state: BeaconState,
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aggregator_index: ValidatorIndex,
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aggregate: Attestation,
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privkey: int) -> LightAggregateAndProof:
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return LightAggregateAndProof(
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aggregator_index=aggregator_index,
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aggregate=aggregate,
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selection_proof=get_light_client_slot_signature(state, aggregate.data.slot, privkey),
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)
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```
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Then `signed_light_aggregate_and_proof = SignedLightAggregateAndProof(message=light_aggregate_and_proof, signature=signature)` is constructed and broadast. Where `signature` is obtained from:
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```python
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def get_light_aggregate_and_proof_signature(state: BeaconState,
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aggregate_and_proof: LightAggregateAndProof,
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privkey: int) -> BLSSignature:
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aggregate = aggregate_and_proof.aggregate
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domain = get_domain(state, DOMAIN_CLIENT_AGGREGATE_AND_PROOF, compute_epoch_at_slot(aggregate.data.slot))
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signing_root = compute_signing_root(aggregate_and_proof, domain)
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return bls.Sign(privkey, signing_root)
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```
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##### `LightAggregateAndProof`
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```python
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class LightAggregateAndProof(Container):
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aggregator_index: ValidatorIndex
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aggregate: Attestation
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selection_proof: BLSSignature
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```
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##### `SignedLightAggregateAndProof`
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```python
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class SignedLightAggregateAndProof(Container):
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message: LightAggregateAndProof
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signature: BLSSignature
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```
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