Merge pull request #2438 from ralexstokes/add-aggregate-pks-fn

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 +311,11 @@ class SpecBuilder(ABC):
         """
         raise NotImplementedError()
 
+    @classmethod
+    @abstractmethod
+    def implement_optimizations(cls, functions: Dict[str, str]) -> Dict[str, str]:
+        raise NotImplementedError()
+
     @classmethod
     @abstractmethod
     def build_spec(cls, preset_name: str,
@@ -429,6 +440,10 @@ get_attesting_indices = cache_this(
     def invariant_checks(cls) -> str:
         return ''
 
+    @classmethod
+    def implement_optimizations(cls, functions: Dict[str, str]) -> Dict[str, str]:
+        return functions
+
     @classmethod
     def build_spec(cls, preset_name: str,
                    source_files: Sequence[Path], preset_files: Sequence[Path], config_file: Path) -> str:
@@ -482,6 +497,11 @@ assert (
     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:
+            functions["eth2_aggregate_pubkeys"] = OPTIMIZED_BLS_AGGREGATE_PUBKEYS.strip()
+        return super().implement_optimizations(functions)
 
 #
 # MergeSpecBuilder
@@ -588,7 +608,8 @@ def objects_to_spec(preset_name: 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():
@@ -853,6 +874,7 @@ class PySpecCommand(Command):
                     specs/phase0/validator.md
                     specs/phase0/weak-subjectivity.md
                     specs/altair/beacon-chain.md
+                    specs/altair/bls.md
                     specs/altair/fork.md
                     specs/altair/validator.md
                     specs/altair/p2p-interface.md

specs/altair/beacon-chain.md

@@ -26,8 +26,7 @@
     - [`SyncAggregate`](#syncaggregate)
     - [`SyncCommittee`](#synccommittee)
 - [Helper functions](#helper-functions)
-  - [`Predicates`](#predicates)
+  - [Crypto](#crypto)
-    - [`eth2_fast_aggregate_verify`](#eth2_fast_aggregate_verify)
   - [Misc](#misc-1)
     - [`add_flag`](#add_flag)
     - [`has_flag`](#has_flag)
@@ -107,7 +106,6 @@ Altair is the first beacon chain hard fork. Its main features are:
 
 | Name | Value |
 | - | - |
-| `G2_POINT_AT_INFINITY` | `BLSSignature(b'\xc0' + b'\x00' * 95)` |
 | `PARTICIPATION_FLAG_WEIGHTS` | `[TIMELY_SOURCE_WEIGHT, TIMELY_TARGET_WEIGHT, TIMELY_HEAD_WEIGHT]` |
 
 ## Preset
@@ -220,19 +218,11 @@ class SyncCommittee(Container):
 
 ## Helper functions
 
-### `Predicates`
+### Crypto
 
-#### `eth2_fast_aggregate_verify`
+Refer to the definitions in the [phase 0 document regarding BLS signatures](../phase0/beacon-chain.md#bls-signatures)
-
+and the extensions defined in the [Altair BLS document](./bls.md). This specification assumes knowledge of
-```python
+the functionality described in those documents.
-def eth2_fast_aggregate_verify(pubkeys: Sequence[BLSPubkey], message: Bytes32, signature: BLSSignature) -> bool:
-    """
-    Wrapper to ``bls.FastAggregateVerify`` accepting the ``G2_POINT_AT_INFINITY`` signature when ``pubkeys`` is empty.
-    """
-    if len(pubkeys) == 0 and signature == G2_POINT_AT_INFINITY:
-        return True
-    return bls.FastAggregateVerify(pubkeys, message, signature)
-```
 
 ### Misc
 
@@ -297,7 +287,7 @@ 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)
 ```
 

specs/altair/bls.md

@@ -0,0 +1,65 @@
+# Ethereum 2.0 Altair BLS extensions
+
+## Table of contents
+
+<!-- TOC -->
+<!-- START doctoc generated TOC please keep comment here to allow auto update -->
+<!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE -->
+
+- [Introduction](#introduction)
+- [Constants](#constants)
+- [Extensions](#extensions)
+  - [`eth2_aggregate_pubkeys`](#eth2_aggregate_pubkeys)
+  - [`eth2_fast_aggregate_verify`](#eth2_fast_aggregate_verify)
+
+<!-- END doctoc generated TOC please keep comment here to allow auto update -->
+<!-- /TOC -->
+
+## Introduction
+
+A number of extensions are defined to handle BLS signatures in the Altair upgrade.
+
+Knowledge of the [phase 0 specification](../phase0/beacon-chain.md) is assumed, including type definitions.
+
+## Constants
+
+| Name | Value |
+| - | - |
+| `G2_POINT_AT_INFINITY` | `BLSSignature(b'\xc0' + b'\x00' * 95)` |
+
+## Extensions
+
+### `eth2_aggregate_pubkeys`
+
+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
+```
+
+### `eth2_fast_aggregate_verify`
+
+```python
+def eth2_fast_aggregate_verify(pubkeys: Sequence[BLSPubkey], message: Bytes32, signature: BLSSignature) -> bool:
+    """
+    Wrapper to ``bls.FastAggregateVerify`` accepting the ``G2_POINT_AT_INFINITY`` signature when ``pubkeys`` is empty.
+    """
+    if len(pubkeys) == 0 and signature == G2_POINT_AT_INFINITY:
+        return True
+    return bls.FastAggregateVerify(pubkeys, message, signature)
+```