initially implement specified attestation aggregation functions and data structures

beacon_chain/naive_attestation_aggregation.nim

@@ -0,0 +1,28 @@
+import
+  sequtils,
+  ./spec/[datatypes, crypto, digest, helpers, validator],
+  ./ssz
+
+# https://github.com/ethereum/eth2.0-specs/blob/v0.9.2/specs/validator/0_beacon-chain-validator.md#aggregation-selection
+func get_slot_signature(state: BeaconState, slot: Slot, privkey: ValidatorPrivKey):
+    ValidatorSig =
+  # TODO privkey is int in spec, but bls_sign wants a ValidatorPrivKey
+  let domain =
+    get_domain(state, DOMAIN_BEACON_ATTESTER, compute_epoch_at_slot(slot))
+  bls_sign(privkey, hash_tree_root(slot).data, domain)
+
+# https://github.com/ethereum/eth2.0-specs/blob/v0.9.2/specs/validator/0_beacon-chain-validator.md#aggregation-selection
+func is_aggregator(state: BeaconState, slot: Slot, index: uint64,
+    slot_signature: ValidatorSig): bool =
+  # TODO index is a CommitteeIndex, aka uint64
+  var cache = get_empty_per_epoch_cache()
+
+  let
+    committee = get_beacon_committee(state, slot, index, cache)
+    modulo = max(1, len(committee) div TARGET_AGGREGATORS_PER_COMMITTEE).uint64
+  bytes_to_int(eth2hash(slot_signature.getBytes).data[0..7]) mod modulo == 0
+
+# https://github.com/ethereum/eth2.0-specs/blob/v0.9.2/specs/validator/0_beacon-chain-validator.md#aggregate-signature-1
+func get_aggregate_signature(attestations: seq[Attestation]): ValidatorSig =
+  let signatures = mapIt(attestations, it.signature)
+  bls_aggregate_signatures(signatures)

beacon_chain/spec/crypto.nim

@@ -128,6 +128,9 @@ func init(T: type VerKey): VerKey =
 func init(T: type SigKey): SigKey =
   result.point.inf()
 
+func init(T: type Signature): Signature =
+  result.point.inf()
+
 func combine*[T](values: openarray[BlsValue[T]]): BlsValue[T] =
   result = BlsValue[T](kind: Real, blsValue: T.init())
 
@@ -142,6 +145,10 @@ func combine*[T](x: var BlsValue[T], other: BlsValue[T]) =
 func bls_aggregate_pubkeys*(keys: openArray[ValidatorPubKey]): ValidatorPubKey =
   keys.combine()
 
+# https://github.com/ethereum/eth2.0-specs/blob/v0.9.2/specs/bls_signature.md#bls_aggregate_signatures
+func bls_aggregate_signatures*(keys: openArray[ValidatorSig]): ValidatorSig =
+  keys.combine()
+
 # https://github.com/ethereum/eth2.0-specs/blob/v0.9.2/specs/bls_signature.md#bls_verify
 func bls_verify*(
     pubkey: ValidatorPubKey, msg: openArray[byte], sig: ValidatorSig,
@@ -291,4 +298,3 @@ proc toGaugeValue*(hash: Eth2Digest): int64 =
 
 template fromSszBytes*(T: type BlsValue, bytes: openarray[byte]): auto =
   fromBytes(T, bytes)
-

beacon_chain/spec/datatypes.nim

@@ -320,6 +320,11 @@ type
     deposit_count*: uint64
     block_hash*: Eth2Digest
 
+  # https://github.com/ethereum/eth2.0-specs/blob/v0.9.2/specs/validator/0_beacon-chain-validator.md#aggregateandproof
+  AggregateAndProof* = object
+    index: uint64
+    selection_proof: ValidatorSig
+
   # TODO to be replaced with some magic hash caching
   HashedBeaconState* = object
     data*: BeaconState