Ensure non-zero bits for each aggregate committee

specs/electra/beacon-chain.md

@@ -56,6 +56,7 @@
     - [New `get_activation_exit_churn_limit`](#new-get_activation_exit_churn_limit)
     - [New `get_consolidation_churn_limit`](#new-get_consolidation_churn_limit)
     - [New `get_pending_balance_to_withdraw`](#new-get_pending_balance_to_withdraw)
+    - [Modified `get_indexed_attestation`](#modified-get_indexed_attestation)
     - [Modified `get_attesting_indices`](#modified-get_attesting_indices)
     - [Modified `get_next_sync_committee_indices`](#modified-get_next_sync_committee_indices)
   - [Beacon state mutators](#beacon-state-mutators)
@@ -572,6 +573,25 @@ def get_pending_balance_to_withdraw(state: BeaconState, validator_index: Validat
     )
 ```
 
+#### Modified `get_indexed_attestation`
+
+*Note*: The function is modified to use the new `get_attesting_indices`.
+
+```python
+def get_indexed_attestation(state: BeaconState, attestation: Attestation) -> IndexedAttestation:
+    """
+    Return the indexed attestation corresponding to ``attestation``.
+    """
+    # [Modified in Electra:EIP7549]
+    attesting_indices = get_attesting_indices(state, attestation)
+
+    return IndexedAttestation(
+        attesting_indices=sorted(attesting_indices),
+        data=attestation.data,
+        signature=attestation.signature,
+    )
+```
+
 #### Modified `get_attesting_indices`
 
 *Note*: The function `get_attesting_indices` is modified to support EIP7549.
@@ -1254,6 +1274,8 @@ def process_operations(state: BeaconState, body: BeaconBlockBody) -> None:
 
 ###### Modified `process_attestation`
 
+*Note*: The function is modified to support EIP7549.
+
 ```python
 def process_attestation(state: BeaconState, attestation: Attestation) -> None:
     data = attestation.data
@@ -1264,18 +1286,24 @@ def process_attestation(state: BeaconState, attestation: Attestation) -> None:
     # [Modified in Electra:EIP7549]
     assert data.index == 0
     committee_indices = get_committee_indices(attestation.committee_bits)
-    participants_count = 0
+    committee_offset = 0
     for index in committee_indices:
         assert index < get_committee_count_per_slot(state, data.target.epoch)
         committee = get_beacon_committee(state, data.slot, index)
-        participants_count += len(committee)
+        committee_attesters = set(
+            attester_index for i, attester_index in enumerate(committee)
+            if attestation.aggregation_bits[committee_offset + i]
+        )
+        assert len(committee_attesters) > 0
+        committee_offset += len(committee)
 
-    assert len(attestation.aggregation_bits) == participants_count
+    # Bitfield length matches total number of participants
+    assert len(attestation.aggregation_bits) == committee_offset
 
     # Participation flag indices
     participation_flag_indices = get_attestation_participation_flag_indices(state, data, state.slot - data.slot)
 
-    # Verify signature
+    # Verify signature [Modified in Electra:EIP7549]
     assert is_valid_indexed_attestation(state, get_indexed_attestation(state, attestation))
 
     # Update epoch participation flags
@@ -1285,6 +1313,7 @@ def process_attestation(state: BeaconState, attestation: Attestation) -> None:
         epoch_participation = state.previous_epoch_participation
 
     proposer_reward_numerator = 0
+    # [Modified in Electra:EIP7549]
     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):

tests/core/pyspec/eth2spec/test/electra/block_processing/test_process_attestation.py

@@ -1,12 +1,15 @@
+from eth2spec.test.helpers.constants import MINIMAL
 from eth2spec.test.context import (
     always_bls,
     spec_state_test,
     with_electra_and_later,
+    with_presets,
 )
 from eth2spec.test.helpers.attestations import (
     run_attestation_processing,
     get_valid_attestation,
     sign_attestation,
+    get_empty_eip7549_aggregation_bits,
 )
 from eth2spec.test.helpers.state import (
     next_slots,
@@ -79,3 +82,32 @@ def test_invalid_nonset_committe_bits(spec, state):
     attestation.committee_bits[committee_index] = 0
 
     yield from run_attestation_processing(spec, state, attestation, valid=False)
+
+
+@with_electra_and_later
+@spec_state_test
+def test_invalid_nonset_bits_for_one_committee(spec, state):
+    """
+    EIP-7549 test
+    """
+    # Attestation with full committee participating
+    committee_0 = spec.get_beacon_committee(state, state.slot, 0)
+    attestation_1 = get_valid_attestation(spec, state, index=1, signed=True)
+
+    # Create an on chain aggregate
+    aggregate = spec.Attestation(data=attestation_1.data, signature=attestation_1.signature)
+    aggregate.committee_bits[0] = True
+    aggregate.committee_bits[1] = True
+    aggregate.aggregation_bits = get_empty_eip7549_aggregation_bits(
+        spec, state, aggregate.committee_bits, aggregate.data.slot
+    )
+    committee_offset = len(committee_0)
+    for i in range(len(attestation_1.aggregation_bits)):
+        aggregate.aggregation_bits[committee_offset + i] = attestation_1.aggregation_bits[i]
+
+    # Check that only one committee is presented
+    assert spec.get_attesting_indices(state, aggregate) == spec.get_attesting_indices(state, attestation_1)
+
+    next_slots(spec, state, spec.MIN_ATTESTATION_INCLUSION_DELAY)
+
+    yield from run_attestation_processing(spec, state, aggregate, valid=False)