initial simple/naive attestation aggregation

beacon_chain/attestation_aggregation.nim

@@ -0,0 +1,86 @@
+# beacon_chain
+# Copyright (c) 2018-2019 Status Research & Development GmbH
+# Licensed and distributed under either of
+#   * MIT license (license terms in the root directory or at http://opensource.org/licenses/MIT).
+#   * Apache v2 license (license terms in the root directory or at http://www.apache.org/licenses/LICENSE-2.0).
+# at your option. This file may not be copied, modified, or distributed except according to those terms.
+
+# Have an an aggregated aggregation ready for broadcast at
+# SECONDS_PER_SLOT * 2 / 3, i.e. 2/3 through relevant slot
+# intervals.
+#
+# The other part is arguably part of attestation pool -- the validation's
+# something that should be happing on receipt, not aggregation per se. In
+# that part, check that messages conform -- so, check for each type
+# https://github.com/ethereum/eth2.0-specs/blob/v0.9.2/specs/networking/p2p-interface.md#topics-and-messages
+# specifies. So by the time this calls attestation pool, all validation's
+# already done.
+#
+# Finally, some of the filtering's libp2p stuff. Consistency checks between
+# topic/message types and GOSSIP_MAX_SIZE -- mostly doesn't belong here, so
+# while TODO, isn't TODO for this module.
+
+import
+  options,
+  ./spec/[beaconstate, datatypes, crypto, digest, helpers, validator],
+  ./attestation_pool, ./beacon_node_types, ./ssz
+
+# TODO gossipsub validation lives somewhere, maybe here
+# TODO add tests, especially for validation
+# https://github.com/status-im/nim-beacon-chain/issues/122#issuecomment-562479965
+
+const
+  # https://github.com/ethereum/eth2.0-specs/blob/v0.9.2/specs/networking/p2p-interface.md#configuration
+  ATTESTATION_PROPAGATION_SLOT_RANGE = 32
+
+# 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 =
+  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
+
+proc aggregate_attestations*(
+    pool: AttestationPool, state: BeaconState, index: uint64,
+    privkey: ValidatorPrivKey): Option[AggregateAndProof] =
+  # TODO alias CommitteeIndex to actual type then convert various uint64's here
+
+  let
+    slot = state.slot - 2
+    slot_signature = get_slot_signature(state, slot, privkey)
+
+  if slot < 0:
+    return none(AggregateAndProof)
+  doAssert slot + ATTESTATION_PROPAGATION_SLOT_RANGE >= state.slot
+  doAssert state.slot >= slot
+
+  # https://github.com/ethereum/eth2.0-specs/blob/v0.9.2/specs/validator/0_beacon-chain-validator.md#aggregation-selection
+  if not is_aggregator(state, slot, index, slot_signature):
+    return none(AggregateAndProof)
+
+  let attestation_data =
+    makeAttestationData(state, slot, index, get_block_root_at_slot(state, slot))
+
+  # https://github.com/ethereum/eth2.0-specs/blob/v0.9.2/specs/validator/0_beacon-chain-validator.md#construct-aggregate
+  for attestation in getAttestationsForBlock(pool, state, slot):
+    if attestation.data == attestation_data:
+      # https://github.com/ethereum/eth2.0-specs/blob/v0.9.2/specs/validator/0_beacon-chain-validator.md#aggregateandproof
+      return some(AggregateAndProof(
+        aggregator_index: index,
+        aggregate: attestation,
+        selection_proof: slot_signature))
+
+  # TODO in catch-up mode, we could get here, so probably shouldn't assert
+  doAssert false
+  none(AggregateAndProof)

beacon_chain/spec/crypto.nim

@@ -151,6 +151,9 @@ 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())
 
@@ -165,6 +168,10 @@ 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,
@@ -314,4 +321,3 @@ proc toGaugeValue*(hash: Eth2Digest): int64 =
 
 template fromSszBytes*(T: type BlsValue, bytes: openarray[byte]): auto =
   fromBytes(T, bytes)
-

beacon_chain/spec/datatypes.nim

@@ -320,6 +320,12 @@ 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
+    aggregator_index*: uint64
+    aggregate*: Attestation
+    selection_proof*: ValidatorSig
+
   # TODO to be replaced with some magic hash caching
   HashedBeaconState* = object
     data*: BeaconState