Separate type for aggregated committee attestation

specs/electra/beacon-chain.md

@@ -31,6 +31,7 @@
     - [`WithdrawalRequest`](#withdrawalrequest)
     - [`ConsolidationRequest`](#consolidationrequest)
     - [`SingleAttestation`](#singleattestation)
+    - [`CommitteeAttestation`](#committeeattestation)
     - [`ExecutionRequests`](#executionrequests)
   - [Modified Containers](#modified-containers)
     - [`AttesterSlashing`](#attesterslashing)
@@ -281,6 +282,16 @@ class SingleAttestation(Container):
     signature: BLSSignature
 ```
 
+#### `CommitteeAttestation`
+
+```python
+class CommitteeAttestation(Container):
+    aggregation_bits: Bitlist[MAX_VALIDATORS_PER_COMMITTEE]
+    data: AttestationData
+    committee_index: CommitteeIndex
+    signature: BLSSignature
+```
+
 #### `ExecutionRequests`
 
 *Note*: This container holds requests from the execution layer that are received in [

specs/electra/p2p-interface.md

@@ -46,10 +46,9 @@ The derivation of the `message-id` remains stable.
 ##### `beacon_aggregate_and_proof`
 
 The following convenience variables are re-defined
-- `index = get_committee_indices(aggregate.committee_bits)[0]`
+- `index = aggregate.committee_index`
 
 The following validations are added:
-* [REJECT] `len(committee_indices) == 1`, where `committee_indices = get_committee_indices(aggregate)`.
 * [REJECT] `aggregate.data.index == 0`
 
 #### Attestation subnets

specs/electra/validator.md

@@ -28,6 +28,7 @@
   - [Construct attestation](#construct-attestation)
 - [Attestation aggregation](#attestation-aggregation)
   - [Construct aggregate](#construct-aggregate)
+  - [Broadcast aggregate](#broadcast-aggregate)
 
 <!-- END doctoc generated TOC please keep comment here to allow auto update -->
 <!-- /TOC -->
@@ -66,7 +67,7 @@ class GetPayloadResponse(object):
 ```python
 class AggregateAndProof(Container):
     aggregator_index: ValidatorIndex
-    aggregate: Attestation  # [Modified in Electra:EIP7549]
+    aggregate: CommitteeAttestation  # [Modified in Electra:EIP7549]
     selection_proof: BLSSignature
 ```
 
@@ -109,22 +110,22 @@ Changed the max attester slashings size to `MAX_ATTESTER_SLASHINGS_ELECTRA`.
 Changed the max attestations size to `MAX_ATTESTATIONS_ELECTRA`.
 
 The network attestation aggregates contain only the assigned committee attestations.
-Attestation aggregates received by the block proposer from the committee aggregators with disjoint `committee_bits` sets and equal `AttestationData` SHOULD be consolidated into a single `Attestation` object.
-The proposer should run the following function to construct an on chain final aggregate form a list of network aggregates with equal `AttestationData`:
+Committee attestations received by the block proposer from the committee aggregators with different `committee_index` sets and equal `AttestationData` SHOULD be consolidated into a single `Attestation` object.
+The proposer should run the following function to construct an on chain final aggregate form a list of committee attestations with equal `AttestationData`:
 
 ```python
-def compute_on_chain_aggregate(network_aggregates: Sequence[Attestation]) -> Attestation:
-    aggregates = sorted(network_aggregates, key=lambda a: get_committee_indices(a.committee_bits)[0])
+def compute_on_chain_aggregate(committee_attestations: Sequence[CommitteeAttestation]) -> Attestation:
+    attestations = sorted(committee_attestations, key=lambda a: a.committee_index)
 
-    data = aggregates[0].data
+    data = attestations[0].data
     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]
+    committee_indices = [a.committee_index for a in aggregates]
     committee_flags = [(index in committee_indices) for index in range(0, MAX_COMMITTEES_PER_SLOT)]
     committee_bits = Bitvector[MAX_COMMITTEES_PER_SLOT](committee_flags)
 
@@ -220,4 +221,30 @@ with updated field assignments:
 
 - Set `attestation_data.index = 0`.
 - 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 bit set corresponding to `committee_index` in each individual attestation.
+- Set `attestation.committee_index = committee_index`, where `committee_index` is the `committee_index` in each individual attestation.
+
+#### Aggregate signature
+
+Set `aggregate_attestation.signature = aggregate_signature` where `aggregate_signature` is obtained from:
+
+```python
+def get_aggregate_signature(attestations: Sequence[CommitteeAttestation]) -> BLSSignature:
+    signatures = [attestation.signature for attestation in attestations]
+    return bls.Aggregate(signatures)
+```
+
+### Broadcast aggregate
+
+`get_aggregate_and_proof` is modified to accept `CommitteeAttestation` for `aggregate`.
+
+```python
+def get_aggregate_and_proof(state: BeaconState,
+                            aggregator_index: ValidatorIndex,
+                            committee_attestation: CommitteeAttestation,
+                            privkey: int) -> AggregateAndProof:
+    return AggregateAndProof(
+        aggregator_index=aggregator_index,
+        aggregate=committee_attestation,
+        selection_proof=get_slot_signature(state, aggregate.data.slot, privkey),
+    )
+```