eth2.0-specs/specs/_features/eip7549/beacon-chain.md

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# EIP-7549 -- The Beacon Chain
## Table of contents
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- [Introduction](#introduction)
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- [Preset](#preset)
- [Containers](#containers)
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- [Modified containers](#modified-containers)
- [Attestation](#attestation)
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- [IndexedAttestation](#indexedattestation)
- [Helper functions](#helper-functions)
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- [Misc](#misc)
- [`get_committee_indices`](#get_committee_indices)
- [Beacon state accessors](#beacon-state-accessors)
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- [New `get_committee_attesters`](#new-get_committee_attesters)
- [Modified `get_attesting_indices`](#modified-get_attesting_indices)
- [Block processing](#block-processing)
- [Modified `process_attestation`](#modified-process_attestation)
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## Introduction
This is the beacon chain specification to move the attestation committee index outside of the signed message. For motivation, refer to [EIP-7549](https://eips.ethereum.org/EIPS/eip-7549).
*Note:* This specification is built upon [Deneb](../../deneb/beacon_chain.md) and is under active development.
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## Preset
| Name | Value | Description |
| - | - | - |
| `MAX_ATTESTER_SLASHINGS` | `2**0` (= 1) |
| `MAX_ATTESTATIONS` | `2**3` (= 8) |
## Containers
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### Modified containers
#### `Attestation`
```python
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class Attestation(Container):
aggregation_bits: List[Bitlist[MAX_VALIDATORS_PER_COMMITTEE], MAX_COMMITTEES_PER_SLOT] # [Modified in EIP7549]
data: AttestationData
committee_bits: Bitvector[MAX_COMMITTEES_PER_SLOT] # [New in EIP7549]
signature: BLSSignature
```
#### `IndexedAttestation`
```python
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class IndexedAttestation(Container):
# [Modified in EIP7549]
attesting_indices: List[ValidatorIndex, MAX_VALIDATORS_PER_COMMITTEE * MAX_COMMITTEES_PER_SLOT]
data: AttestationData
signature: BLSSignature
```
## Helper functions
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### Misc
#### `get_committee_indices`
```python
def get_committee_indices(commitee_bits: Bitvector) -> List[CommitteeIndex]:
return [CommitteeIndex(index) for bit, index in enumerate(commitee_bits) if bit]
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```
### Beacon state accessors
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#### New `get_committee_attesters`
```python
def get_committee_attesters(state: BeaconState, data: AttestationData,
attesting_bits: Bitlist, index: CommitteeIndex) -> Set[ValidatorIndex]:
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committee = get_beacon_committee(state, data.slot, index)
return set(index for i, index in enumerate(committee) if attesting_bits[i])
```
#### Modified `get_attesting_indices`
```python
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def get_attesting_indices(state: BeaconState, attestation: Attestation) -> Set[ValidatorIndex]:
"""
Return the set of attesting indices corresponding to ``aggregation_bits`` and ``committee_bits``.
"""
output = set()
committee_indices = get_committee_indices(attestation.committee_bits)
for index in committee_indices:
attesting_bits = attestation.attesting_bits[index]
committee_attesters = get_committee_attesters(state, attestation.data, attesting_bits, index)
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output = output.union(committee_attesters)
return output
```
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### Block processing
#### Modified `process_attestation`
```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
# [Modified in EIP7549]
assert data.index == 0
committee_indices = get_committee_indices(attestation.committee_bits)
assert len(committee_indices) > 0
assert len(committee_indices) == len(attestation.aggregation_bits)
for index in committee_indices:
assert index < get_committee_count_per_slot(state, data.target.epoch)
committee = get_beacon_committee(state, data.slot, index)
assert len(attestation.aggregation_bits[index]) == 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, attestation):
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)
```