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Use 16-bit random value in validator filter #4039

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merged 2 commits into from
Dec 13, 2024
+15 −9
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Use 16-bit random value in validator filter #4039

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db25c9d
Use 16-bit random value in validator filter
jtraglia Dec 4, 2024
01a92dc
Merge branch 'dev' into 16-bit-filter
jtraglia Dec 13, 2024
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24 changes: 15 additions & 9 deletions specs/electra/beacon-chain.md
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Original file line number Diff line number Diff line change
Expand Up @@ -427,23 +427,26 @@ class BeaconState(Container):

#### Modified `compute_proposer_index`

*Note*: The function `compute_proposer_index` is modified to use `MAX_EFFECTIVE_BALANCE_ELECTRA`.
*Note*: The function `compute_proposer_index` is modified to use `MAX_EFFECTIVE_BALANCE_ELECTRA` and to use a 16-bit random value instead of an 8-bit random byte in the effective balance filter.

```python
def compute_proposer_index(state: BeaconState, indices: Sequence[ValidatorIndex], seed: Bytes32) -> ValidatorIndex:
"""
Return from ``indices`` a random index sampled by effective balance.
"""
assert len(indices) > 0
MAX_RANDOM_BYTE = 2**8 - 1
MAX_RANDOM_VALUE = 2**16 - 1 # [Modified in Electra]
i = uint64(0)
total = uint64(len(indices))
while True:
candidate_index = indices[compute_shuffled_index(i % total, total, seed)]
random_byte = hash(seed + uint_to_bytes(uint64(i // 32)))[i % 32]
# [Modified in Electra]
random_bytes = hash(seed + uint_to_bytes(i // 16))
offset = i % 16 * 2
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noting we get the intended change here as precedence in python gives us this (i % 16) * 2

random_value = bytes_to_uint64(random_bytes[offset:offset + 2])
effective_balance = state.validators[candidate_index].effective_balance
# [Modified in Electra:EIP7251]
if effective_balance * MAX_RANDOM_BYTE >= MAX_EFFECTIVE_BALANCE_ELECTRA * random_byte:
if effective_balance * MAX_RANDOM_VALUE >= MAX_EFFECTIVE_BALANCE_ELECTRA * random_value:
return candidate_index
i += 1
```
Expand Down Expand Up @@ -617,7 +620,7 @@ def get_attesting_indices(state: BeaconState, attestation: Attestation) -> Set[V

#### Modified `get_next_sync_committee_indices`

*Note*: The function `get_next_sync_committee_indices` is modified to use `MAX_EFFECTIVE_BALANCE_ELECTRA`.
*Note*: The function `get_next_sync_committee_indices` is modified to use `MAX_EFFECTIVE_BALANCE_ELECTRA` and to use a 16-bit random value instead of an 8-bit random byte in the effective balance filter.

```python
def get_next_sync_committee_indices(state: BeaconState) -> Sequence[ValidatorIndex]:
Expand All @@ -626,19 +629,22 @@ def get_next_sync_committee_indices(state: BeaconState) -> Sequence[ValidatorInd
"""
epoch = Epoch(get_current_epoch(state) + 1)

MAX_RANDOM_BYTE = 2**8 - 1
MAX_RANDOM_VALUE = 2**16 - 1 # [Modified in Electra]
active_validator_indices = get_active_validator_indices(state, epoch)
active_validator_count = uint64(len(active_validator_indices))
seed = get_seed(state, epoch, DOMAIN_SYNC_COMMITTEE)
i = 0
i = uint64(0)
sync_committee_indices: List[ValidatorIndex] = []
while len(sync_committee_indices) < SYNC_COMMITTEE_SIZE:
shuffled_index = compute_shuffled_index(uint64(i % active_validator_count), active_validator_count, seed)
candidate_index = active_validator_indices[shuffled_index]
random_byte = hash(seed + uint_to_bytes(uint64(i // 32)))[i % 32]
# [Modified in Electra]
random_bytes = hash(seed + uint_to_bytes(i // 16))
offset = i % 16 * 2
random_value = bytes_to_uint64(random_bytes[offset:offset + 2])
effective_balance = state.validators[candidate_index].effective_balance
# [Modified in Electra:EIP7251]
if effective_balance * MAX_RANDOM_BYTE >= MAX_EFFECTIVE_BALANCE_ELECTRA * random_byte:
if effective_balance * MAX_RANDOM_VALUE >= MAX_EFFECTIVE_BALANCE_ELECTRA * random_value:
sync_committee_indices.append(candidate_index)
i += 1
return sync_committee_indices
Expand Down