split DlogGroup so we have a separate trait for MSM methods (#380)

Author: srinathsetty

src/provider/bn256_grumpkin.rs

@@ -3,7 +3,7 @@ use crate::{
   impl_traits,
   provider::{
     msm::{msm, msm_small},
-    traits::{DlogGroup, PairingGroup},
+    traits::{DlogGroup, DlogGroupExt, PairingGroup},
   },
   traits::{Group, PrimeFieldExt, TranscriptReprTrait},
 };
@@ -83,17 +83,6 @@ impl Group for G2 {
 impl DlogGroup for G2 {
   type AffineGroupElement = G2Affine;
 
-  fn vartime_multiscalar_mul(scalars: &[Self::Scalar], bases: &[Self::AffineGroupElement]) -> Self {
-    msm(scalars, bases)
-  }
-
-  fn vartime_multiscalar_mul_small<T: Integer + Into<u64> + Copy + Sync + ToPrimitive>(
-    scalars: &[T],
-    bases: &[Self::AffineGroupElement],
-  ) -> Self {
-    msm_small(scalars, bases)
-  }
-
   fn affine(&self) -> Self::AffineGroupElement {
     self.to_affine()
   }

src/provider/hyperkzg.rs

@@ -12,7 +12,7 @@ use crate::{
   provider::{
     ptau::PtauFileError,
     read_ptau,
-    traits::{DlogGroup, PairingGroup},
+    traits::{DlogGroup, DlogGroupExt, PairingGroup},
     write_ptau,
   },
   traits::{

src/provider/pasta.rs

@@ -3,7 +3,7 @@ use crate::{
   impl_traits,
   provider::{
     msm::{msm, msm_small},
-    traits::DlogGroup,
+    traits::{DlogGroup, DlogGroupExt},
   },
   traits::{Group, PrimeFieldExt, TranscriptReprTrait},
 };

src/provider/pedersen.rs

@@ -4,7 +4,7 @@ use crate::{
   gadgets::utils::to_bignat_repr,
   provider::{
     ptau::{read_points, write_points, PtauFileError},
-    traits::DlogGroup,
+    traits::{DlogGroup, DlogGroupExt},
   },
   traits::{
     commitment::{CommitmentEngineTrait, CommitmentTrait, Len},
@@ -203,7 +203,7 @@ where
 
 impl<E: Engine> CommitmentEngineTrait<E> for CommitmentEngine<E>
 where
-  E::GE: DlogGroup,
+  E::GE: DlogGroupExt,
 {
   type CommitmentKey = CommitmentKey<E>;
   type Commitment = Commitment<E>;
@@ -307,10 +307,9 @@ where
     Self: Sized;
 }
 
-impl<E> CommitmentKeyExtTrait<E> for CommitmentKey<E>
+impl<E: Engine<CE = CommitmentEngine<E>>> CommitmentKeyExtTrait<E> for CommitmentKey<E>
 where
-  E: Engine<CE = CommitmentEngine<E>>,
-  E::GE: DlogGroup,
+  E::GE: DlogGroupExt,
 {
   fn split_at(&self, n: usize) -> (CommitmentKey<E>, CommitmentKey<E>) {
     (

src/provider/secp_secq.rs

@@ -3,7 +3,7 @@ use crate::{
   impl_traits,
   provider::{
     msm::{msm, msm_small},
-    traits::DlogGroup,
+    traits::{DlogGroup, DlogGroupExt},
   },
   traits::{Group, PrimeFieldExt, TranscriptReprTrait},
 };

src/provider/traits.rs

@@ -28,7 +28,7 @@ impl<T, Rhs, Output> GroupOpsOwned<Rhs, Output> for T where T: for<'r> GroupOps<
 pub trait ScalarMulOwned<Rhs, Output = Self>: for<'r> ScalarMul<&'r Rhs, Output> {}
 impl<T, Rhs, Output> ScalarMulOwned<Rhs, Output> for T where T: for<'r> ScalarMul<&'r Rhs, Output> {}
 
-/// A trait that defines extensions to the Group trait
+/// A trait that defines the core discrete logarithm group functionality
 pub trait DlogGroup:
   Group
   + Serialize
@@ -51,6 +51,27 @@ pub trait DlogGroup:
     + CurveAffine
     + SerdeObject;
 
+  /// Produce a vector of group elements using a static label
+  fn from_label(label: &'static [u8], n: usize) -> Vec<Self::AffineGroupElement>;
+
+  /// Produces a preprocessed element
+  fn affine(&self) -> Self::AffineGroupElement;
+
+  /// Returns a group element from a preprocessed group element
+  fn group(p: &Self::AffineGroupElement) -> Self;
+
+  /// Returns an element that is the additive identity of the group
+  fn zero() -> Self;
+
+  /// Returns the generator of the group
+  fn gen() -> Self;
+
+  /// Returns the affine coordinates (x, y, infinity) for the point
+  fn to_coordinates(&self) -> (<Self as Group>::Base, <Self as Group>::Base, bool);
+}
+
+/// Extension trait for DlogGroup that provides multi-scalar multiplication operations
+pub trait DlogGroupExt: DlogGroup {
   /// A method to compute a multiexponentation
   fn vartime_multiscalar_mul(scalars: &[Self::Scalar], bases: &[Self::AffineGroupElement]) -> Self;
 
@@ -81,29 +102,11 @@ pub trait DlogGroup:
       .map(|scalar| Self::vartime_multiscalar_mul_small(scalar, &bases[..scalar.len()]))
       .collect::<Vec<_>>()
   }
-
-  /// Produce a vector of group elements using a static label
-  fn from_label(label: &'static [u8], n: usize) -> Vec<Self::AffineGroupElement>;
-
-  /// Produces a preprocessed element
-  fn affine(&self) -> Self::AffineGroupElement;
-
-  /// Returns a group element from a preprocessed group element
-  fn group(p: &Self::AffineGroupElement) -> Self;
-
-  /// Returns an element that is the additive identity of the group
-  fn zero() -> Self;
-
-  /// Returns the generator of the group
-  fn gen() -> Self;
-
-  /// Returns the affine coordinates (x, y, infinity) for the point
-  fn to_coordinates(&self) -> (<Self as Group>::Base, <Self as Group>::Base, bool);
 }
 
 /// A trait that defines extensions to the DlogGroup trait, to be implemented for
 /// elliptic curve groups that are pairing friendly
-pub trait PairingGroup: DlogGroup {
+pub trait PairingGroup: DlogGroupExt {
   /// A type representing the second group
   type G2: DlogGroup<Scalar = Self::Scalar, Base = Self::Base>;
 
@@ -141,20 +144,6 @@ macro_rules! impl_traits {
     impl DlogGroup for $name::Point {
       type AffineGroupElement = $name::Affine;
 
-      fn vartime_multiscalar_mul(
-        scalars: &[Self::Scalar],
-        bases: &[Self::AffineGroupElement],
-      ) -> Self {
-        msm(scalars, bases)
-      }
-
-      fn vartime_multiscalar_mul_small<T: Integer + Into<u64> + Copy + Sync + ToPrimitive>(
-        scalars: &[T],
-        bases: &[Self::AffineGroupElement],
-      ) -> Self {
-        msm_small(scalars, bases)
-      }
-
       fn affine(&self) -> Self::AffineGroupElement {
         self.to_affine()
       }
@@ -229,6 +218,22 @@ macro_rules! impl_traits {
       }
     }
 
+    impl DlogGroupExt for $name::Point {
+      fn vartime_multiscalar_mul(
+        scalars: &[Self::Scalar],
+        bases: &[Self::AffineGroupElement],
+      ) -> Self {
+        msm(scalars, bases)
+      }
+
+      fn vartime_multiscalar_mul_small<T: Integer + Into<u64> + Copy + Sync + ToPrimitive>(
+        scalars: &[T],
+        bases: &[Self::AffineGroupElement],
+      ) -> Self {
+        msm_small(scalars, bases)
+      }
+    }
+
     impl PrimeFieldExt for $name::Scalar {
       fn from_uniform(bytes: &[u8]) -> Self {
         let bytes_arr: [u8; 64] = bytes.try_into().unwrap();