Move BLS extensions to new file in Altair

setup.py

@@ -55,6 +55,12 @@ def floorlog2(x: int) -> uint64:
 '''
 
 
+OPTIMIZED_BLS_AGGREGATE_PUBKEYS = '''
+def eth2_aggregate_pubkeys(pubkeys: Sequence[BLSPubkey]) -> BLSPubkey:
+    return bls.AggregatePKs(pubkeys)
+'''
+
+
 class ProtocolDefinition(NamedTuple):
     # just function definitions currently. May expand with configuration vars in future.
     functions: Dict[str, str]
@@ -305,6 +311,10 @@ def invariant_checks(cls) -> str:
         """
         raise NotImplementedError()
 
+    @classmethod
+    def implement_optimizations(cls, functions: Dict[str, str]) -> Dict[str, str]:
+        return functions
+
     @classmethod
     @abstractmethod
     def build_spec(cls, preset_name: str,
@@ -482,6 +492,10 @@ def invariant_checks(cls) -> str:
     TIMELY_HEAD_WEIGHT + TIMELY_SOURCE_WEIGHT + TIMELY_TARGET_WEIGHT + SYNC_REWARD_WEIGHT + PROPOSER_WEIGHT
 ) == WEIGHT_DENOMINATOR'''
 
+    @classmethod
+    def implement_optimizations(cls, functions: Dict[str, str]) -> Dict[str, str]:
+        if "eth2_aggregate_pubkeys" in functions:
+            return {**functions, **{"eth2_aggregate_pubkeys": OPTIMIZED_BLS_AGGREGATE_PUBKEYS.strip()}}
 
 #
 # MergeSpecBuilder
@@ -588,7 +602,8 @@ def format_protocol(protocol_name: str, protocol_def: ProtocolDefinition) -> str
     for k in list(spec_object.functions):
         if "ceillog2" in k or "floorlog2" in k:
             del spec_object.functions[k]
-    functions_spec = '\n\n\n'.join(spec_object.functions.values())
+    functions = builder.implement_optimizations(spec_object.functions)
+    functions_spec = '\n\n\n'.join(functions.values())
 
     # Access global dict of config vars for runtime configurables
     for name in spec_object.config_vars.keys():
@@ -831,7 +846,7 @@ def initialize_options(self):
         self.out_dir = 'pyspec_output'
         self.build_targets = """
                 minimal:presets/minimal:configs/minimal.yaml
-                mainnet:presets/mainnet:configs/mainnet.yaml        
+                mainnet:presets/mainnet:configs/mainnet.yaml
         """
 
     def finalize_options(self):

specs/altair/beacon-chain.md

@@ -26,6 +26,8 @@
     - [`SyncAggregate`](#syncaggregate)
     - [`SyncCommittee`](#synccommittee)
 - [Helper functions](#helper-functions)
+  - [Crypto](#crypto)
+    - [BLS public keys](#bls-public-keys)
   - [`Predicates`](#predicates)
     - [`eth2_fast_aggregate_verify`](#eth2_fast_aggregate_verify)
   - [Misc](#misc-1)
@@ -221,6 +223,32 @@ class SyncCommittee(Container):
 
 ## Helper functions
 
+
+### Crypto
+
+#### BLS public keys
+
+An additional function `AggregatePKs` is defined to extend the
+[IETF BLS signature draft standard v4](https://tools.ietf.org/html/draft-irtf-cfrg-bls-signature-04)
+spec referenced in the phase 0 document.
+
+```python
+def eth2_aggregate_pubkeys(pubkeys: Sequence[BLSPubkey]) -> BLSPubkey:
+    """
+    Return the aggregate public key for the public keys in ``pubkeys``.
+
+    NOTE: the ``+`` operation should be interpreted as elliptic curve point addition, which takes as input
+    elliptic curve points that must be decoded from the input ``BLSPubkey``s.
+    This implementation is for demonstrative purposes only and ignores encoding/decoding concerns.
+    Refer to the BLS signature draft standard for more information.
+    """
+    assert len(pubkeys) > 0
+    result = copy(pubkeys[0])
+    for pubkey in pubkeys[1:]:
+        result += pubkey
+    return result
+```
+
 ### `Predicates`
 
 #### `eth2_fast_aggregate_verify`
@@ -310,7 +338,7 @@ def get_next_sync_committee(state: BeaconState) -> SyncCommittee:
     """
     indices = get_next_sync_committee_indices(state)
     pubkeys = [state.validators[index].pubkey for index in indices]
-    aggregate_pubkey = bls.AggregatePKs(pubkeys)
+    aggregate_pubkey = eth2_aggregate_pubkeys(pubkeys)
     return SyncCommittee(pubkeys=pubkeys, aggregate_pubkey=aggregate_pubkey)
 ```