Merge pull request #3714 from kevaundray/kw/use-optimized-bls-msm

chore: use py-arkworks's multi-exp method inside of `g1_lincomb` and `g2_lincomb`

pysetup/spec_builders/deneb.py

@@ -17,6 +17,7 @@ from eth2spec.capella import {preset_name} as capella
     def preparations(cls):
         return '''
 T = TypeVar('T')  # For generic function
+TPoint = TypeVar('TPoint')  # For generic function. G1 or G2 point.
 '''
 
     @classmethod

specs/_features/eip7594/polynomial-commitments-sampling.md

@@ -130,12 +130,18 @@ def coset_evals_to_cell(coset_evals: CosetEvals) -> Cell:
 ```python
 def g2_lincomb(points: Sequence[G2Point], scalars: Sequence[BLSFieldElement]) -> Bytes96:
     """
-    BLS multiscalar multiplication in G2. This function can be optimized using Pippenger's algorithm and variants.
+    BLS multiscalar multiplication in G2. This can be naively implemented using double-and-add.
     """
     assert len(points) == len(scalars)
-    result = bls.Z2()
-    for x, a in zip(points, scalars):
-        result = bls.add(result, bls.multiply(bls.bytes96_to_G2(x), a))
+
+    if len(points) == 0:
+        return bls.G2_to_bytes96(bls.Z2())
+
+    points_g2 = []
+    for point in points:
+        points_g2.append(bls.bytes96_to_G2(point))
+
+    result = bls.multi_exp(points_g2, scalars)
     return Bytes96(bls.G2_to_bytes96(result))
 ```
 

specs/deneb/polynomial-commitments.md

@@ -18,6 +18,7 @@
     - [`reverse_bits`](#reverse_bits)
     - [`bit_reversal_permutation`](#bit_reversal_permutation)
   - [BLS12-381 helpers](#bls12-381-helpers)
+    - [`multi_exp`](#multi_exp)
     - [`hash_to_bls_field`](#hash_to_bls_field)
     - [`bytes_to_bls_field`](#bytes_to_bls_field)
     - [`bls_field_to_bytes`](#bls_field_to_bytes)
@@ -146,6 +147,18 @@ def bit_reversal_permutation(sequence: Sequence[T]) -> Sequence[T]:
 
 ### BLS12-381 helpers
 
+
+#### `multi_exp`
+
+This function performs a multi-scalar multiplication between `points` and `integers`. `points` can either be in G1 or G2.
+
+```python
+def multi_exp(points: Sequence[TPoint],
+              integers: Sequence[uint64]) -> Sequence[TPoint]:
+    # pylint: disable=unused-argument
+    ...
+```
+
 #### `hash_to_bls_field`
 
 ```python
@@ -274,12 +287,18 @@ def div(x: BLSFieldElement, y: BLSFieldElement) -> BLSFieldElement:
 ```python
 def g1_lincomb(points: Sequence[KZGCommitment], scalars: Sequence[BLSFieldElement]) -> KZGCommitment:
     """
-    BLS multiscalar multiplication. This function can be optimized using Pippenger's algorithm and variants.
+    BLS multiscalar multiplication in G1. This can be naively implemented using double-and-add.
     """
     assert len(points) == len(scalars)
-    result = bls.Z1()
-    for x, a in zip(points, scalars):
-        result = bls.add(result, bls.multiply(bls.bytes48_to_G1(x), a))
+
+    if len(points) == 0:
+        return bls.G1_to_bytes48(bls.Z1())
+
+    points_g1 = []
+    for point in points:
+        points_g1.append(bls.bytes48_to_G1(point))
+
+    result = bls.multi_exp(points_g1, scalars)
     return KZGCommitment(bls.G1_to_bytes48(result))
 ```
 

tests/core/pyspec/eth2spec/utils/bls.py

@@ -225,6 +225,45 @@ def multiply(point, scalar):
     return py_ecc_mul(point, scalar)
 
 
+def multi_exp(points, integers):
+    """
+    Performs a multi-scalar multiplication between
+    `points` and `integers`.
+    `points` can either be in G1 or G2.
+    """
+    # Since this method accepts either G1 or G2, we need to know
+    # the type of the point to return. Hence, we need at least one point.
+    if not points or not integers:
+        raise Exception("Cannot call multi_exp with zero points or zero integers")
+
+    if bls == arkworks_bls or bls == fastest_bls:
+        # Convert integers into arkworks Scalars
+        scalars = []
+        for integer in integers:
+            int_as_bytes = integer.to_bytes(32, 'little')
+            scalars.append(arkworks_Scalar.from_le_bytes(int_as_bytes))
+
+        # Check if we need to perform a G1 or G2 multiexp
+        if isinstance(points[0], arkworks_G1):
+            return arkworks_G1.multiexp_unchecked(points, scalars)
+        elif isinstance(points[0], arkworks_G2):
+            return arkworks_G2.multiexp_unchecked(points, scalars)
+        else:
+            raise Exception("Invalid point type")
+
+    result = None
+    if isinstance(points[0], py_ecc_G1):
+        result = Z1()
+    elif isinstance(points[0], py_ecc_G2):
+        result = Z2()
+    else:
+        raise Exception("Invalid point type")
+
+    for point, scalar in points.zip(integers):
+        result = add(result, multiply(point, scalar))
+    return result
+
+
 def neg(point):
     """
     Returns the point negation of `point`