eip7549: flatten aggregate_bits

specs/_features/eip7549/beacon-chain.md

@@ -44,7 +44,7 @@ This is the beacon chain specification to move the attestation committee index o
 
 ```python
 class Attestation(Container):
-    aggregation_bits: List[Bitlist[MAX_VALIDATORS_PER_COMMITTEE], MAX_COMMITTEES_PER_SLOT]  # [Modified in EIP7549]
+    aggregation_bits: 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
@@ -83,12 +83,15 @@ def get_attesting_indices(state: BeaconState, attestation: Attestation) -> Set[V
 
     output = set()
     committee_indices = get_committee_indices(attestation.committee_bits)
+    committee_offset = 0
     for index in committee_indices:
-        attesting_bits = attestation.aggregation_bits[index]
         committee = get_beacon_committee(state, attestation.data.slot, index)
-        committee_attesters = set(index for i, index in enumerate(committee) if attesting_bits[i])
+        committee_attesters = set(
+            index for i, index in enumerate(committee) if attestation.aggregation_bits[committee_offset + i])
         output = output.union(committee_attesters)
 
+        committee_offset += len(committee)
+
     return output
 ```
 
@@ -106,11 +109,13 @@ def process_attestation(state: BeaconState, attestation: Attestation) -> None:
     # [Modified in EIP7549]
     assert data.index == 0
     committee_indices = get_committee_indices(attestation.committee_bits)
-    assert len(committee_indices) == len(attestation.aggregation_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)
-        assert len(attestation.aggregation_bits[index]) == len(committee)
+        participants_count += len(committee)
+
+    assert len(attestation.aggregation_bits) == participants_count
 
     # Participation flag indices
     participation_flag_indices = get_attestation_participation_flag_indices(state, data, state.slot - data.slot)

specs/_features/eip7549/p2p-interface.md

@@ -36,19 +36,17 @@ The `beacon_aggregate_and_proof` and `beacon_attestation_{subnet_id}` topics are
 
 The following convenience variables are re-defined
 - `index = get_committee_indices(aggregate.committee_bits)[0]`
-- `aggregation_bits = aggregate.aggregation_bits[0]`
 
 The following validations are added:
-* [REJECT] `len(committee_indices) == len(aggregate.attestation_bits) == 1`, where `committee_indices = get_committee_indices(aggregate)`.
+* [REJECT] `len(committee_indices) == 1`, where `committee_indices = get_committee_indices(aggregate)`.
 * [REJECT] `aggregate.data.index == 0`
 
 ###### `beacon_attestation_{subnet_id}`
 
 The following convenience variables are re-defined
 - `index = get_committee_indices(attestation.committee_bits)[0]`
-- `aggregation_bits = attestation.aggregation_bits[0]`
 
 The following validations are added:
-* [REJECT] `len(committee_indices) == len(attestation.attestation_bits) == 1`, where `committee_indices = get_committee_indices(attestation)`.
+* [REJECT] `len(committee_indices) == 1`, where `committee_indices = get_committee_indices(attestation)`.
 * [REJECT] `attestation.data.index == 0`
 

specs/_features/eip7549/validator.md

@@ -35,7 +35,11 @@ def compute_on_chain_aggregate(network_aggregates: List[Attestation]) -> Attesta
     aggregates = sorted(network_aggregates, key=lambda a: get_committee_indices(a.committee_bits)[0])
 
     data = aggregates[0].data
-    aggregation_bits = [a.aggregation_bits[0] for a in aggregates]
+    aggregation_bits = Bitlist[MAX_VALIDATORS_PER_COMMITTEE * MAX_COMMITTEES_PER_SLOT]()
+    for a in aggregates:
+        for b in a.aggregation_bits:
+            aggregation_bits.append(b)
+
     signature = bls.Aggregate([a.signature for a in aggregates])
 
     committee_indices = [get_committee_indices(a.committee_bits)[0] for a in aggregates]
@@ -50,10 +54,8 @@ def compute_on_chain_aggregate(network_aggregates: List[Attestation]) -> Attesta
 #### Construct attestation
 
 - Set `attestation_data.index = 0`.
-- Let `aggregation_bits` be a `Bitlist[MAX_VALIDATORS_PER_COMMITTEE]` of length `len(committee)`, where the bit of the index of the validator in the `committee` is set to `0b1`.
-- Set `attestation.aggregation_bits = [aggregation_bits]`, a list of length 1
-- Let `committee_bits` be a `Bitvector[MAX_COMMITTEES_PER_SLOT]`, where the bit at the index associated with the validator's committee is set to `0b1`
-- Set `attestation.committee_bits = committee_bits`
+- Let `attestation.aggregation_bits` be a `Bitlist[MAX_VALIDATORS_PER_COMMITTEE * MAX_COMMITTEES_PER_SLOT]` of length `len(committee)`, where the bit of the index of the validator in the `committee` is set to `0b1`.
+- Let `attestation.committee_bits` be a `Bitvector[MAX_COMMITTEES_PER_SLOT]`, where the bit at the index associated with the validator's committee is set to `0b1`.
 
 *Note*: Calling `get_attesting_indices(state, attestation)` should return a list of length equal to 1, containing `validator_index`.
 
@@ -62,7 +64,6 @@ def compute_on_chain_aggregate(network_aggregates: List[Attestation]) -> Attesta
 #### Construct aggregate
 
 - Set `attestation_data.index = 0`.
-- Let `aggregation_bits` be a `Bitlist[MAX_VALIDATORS_PER_COMMITTEE]` of length `len(committee)`, where each bit set from each individual attestation is set to `0b1`.
-- Set `attestation.aggregation_bits = [aggregation_bits]`, a list of length 1
-- Set `attestation.committee_bits = committee_bits`, where `committee_bits` has the same value as in each individual attestation
+- Let `aggregation_bits` be a `Bitlist[MAX_VALIDATORS_PER_COMMITTEE * MAX_COMMITTEES_PER_SLOT]` of length `len(committee)`, where each bit set from each individual attestation is set to `0b1`.
+- Set `attestation.committee_bits = committee_bits`, where `committee_bits` has the same value as in each individual attestation.
 

specs/phase0/p2p-interface.md

@@ -367,7 +367,7 @@ The following validations MUST pass before forwarding the `signed_aggregate_and_
 - _[REJECT]_ The aggregate attestation's epoch matches its target -- i.e. `aggregate.data.target.epoch ==
   compute_epoch_at_slot(aggregate.data.slot)`
 - _[REJECT]_ The number of aggregation bits matches the committee size -- i.e.
-  `len(aggregation_bits) == len(get_beacon_committee(state, aggregate.data.slot, aggregate.data.index))`.
+  `len(aggregation_bits) == len(get_beacon_committee(state, aggregate.data.slot, index))`.
 - _[REJECT]_ The aggregate attestation has participants --
   that is, `len(get_attesting_indices(state, aggregate)) >= 1`.
 - _[IGNORE]_ A valid aggregate attestation defined by `hash_tree_root(aggregate.data)` whose `aggregation_bits` is a non-strict superset has _not_ already been seen.