eip7549: Ensure non-zero bits for each committee bitfield comprising an aggregate

specs/electra/beacon-chain.md

@@ -1255,6 +1255,8 @@ 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
@@ -1265,13 +1267,19 @@ 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
-    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_offset = 0
+    for committee_index in committee_indices:
+        assert committee_index < get_committee_count_per_slot(state, data.target.epoch)
+        committee = get_beacon_committee(state, data.slot, committee_index)
+        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)

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

@@ -88,6 +88,7 @@ def test_invalid_nonset_committee_bits(spec, state):
 
 @with_electra_and_later
 @spec_state_test
+@with_presets([MINIMAL], "need multiple committees per slot")
 def test_invalid_nonset_multiple_committee_bits(spec, state):
     """
     EIP-7549 test
@@ -148,3 +149,33 @@ def test_one_committee_with_gap(spec, state):
     next_slots(spec, state, spec.MIN_ATTESTATION_INCLUSION_DELAY)
 
     yield from run_attestation_processing(spec, state, attestation)
+
+
+@with_electra_and_later
+@spec_state_test
+@with_presets([MINIMAL], "need multiple committees per slot")
+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)