Accelerated MSM prep (#41)

* remove send + sync

* introduce a new associative type to capture any form of preprocessing on group elements

* update pasta_curves version

* simplify trait requirements

* fix clippy

Cargo.toml

@@ -22,7 +22,7 @@ rand_core = { version = "0.5", default-features = false }
 rand_chacha = "0.3"
 itertools = "0.9.0"
 subtle = "2.4"
-pasta_curves = "0.3.0"
+pasta_curves = "0.3.1"
 neptune = "6.1"
 generic-array = "0.14.4"
 bellperson-nonnative = { version = "0.2.1", default-features = false, features = ["wasm"] }

src/commitments.rs

@@ -4,6 +4,7 @@ use super::{
 };
 use core::{
   fmt::Debug,
+  marker::PhantomData,
   ops::{Add, AddAssign, Mul, MulAssign},
 };
 use digest::{ExtendableOutput, Input};
@@ -13,7 +14,8 @@ use std::io::Read;
 
 #[derive(Debug)]
 pub struct CommitGens<G: Group> {
-  gens: Vec<G>,
+  gens: Vec<G::PreprocessedGroupElement>,
+  _p: PhantomData<G>,
 }
 
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
@@ -31,14 +33,17 @@ impl<G: Group> CommitGens<G> {
     let mut shake = Shake256::default();
     shake.input(label);
     let mut reader = shake.xof_result();
-    let mut gens: Vec<G> = Vec::new();
+    let mut gens: Vec<G::PreprocessedGroupElement> = Vec::new();
     let mut uniform_bytes = [0u8; 64];
     for _ in 0..n {
       reader.read_exact(&mut uniform_bytes).unwrap();
       gens.push(G::from_uniform_bytes(&uniform_bytes).unwrap());
     }
 
-    CommitGens { gens }
+    CommitGens {
+      gens,
+      _p: PhantomData::default(),
+    }
   }
 }
 

src/pasta.rs

@@ -1,5 +1,6 @@
 //! This module implements the Nova traits for pallas::Point, pallas::Scalar, vesta::Point, vesta::Scalar.
 use crate::traits::{ChallengeTrait, CompressedGroup, Group};
+use core::ops::Mul;
 use ff::Field;
 use merlin::Transcript;
 use pasta_curves::{
@@ -11,7 +12,6 @@ use pasta_curves::{
 use rand::SeedableRng;
 use rand_chacha::ChaCha20Rng;
 use rug::Integer;
-use std::{borrow::Borrow, ops::Mul};
 
 //////////////////////////////////////Pallas///////////////////////////////////////////////
 
@@ -28,27 +28,21 @@ impl PallasCompressedElementWrapper {
   }
 }
 
-unsafe impl Send for PallasCompressedElementWrapper {}
-unsafe impl Sync for PallasCompressedElementWrapper {}
-
 impl Group for pallas::Point {
   type Base = pallas::Base;
   type Scalar = pallas::Scalar;
   type CompressedGroupElement = PallasCompressedElementWrapper;
+  type PreprocessedGroupElement = pallas::Affine;
 
-  fn vartime_multiscalar_mul<I, J>(scalars: I, points: J) -> Self
-  where
-    I: IntoIterator,
-    I::Item: Borrow<Self::Scalar>,
-    J: IntoIterator,
-    J::Item: Borrow<Self>,
-    Self: Clone,
-  {
+  fn vartime_multiscalar_mul(
+    scalars: &[Self::Scalar],
+    bases: &[Self::PreprocessedGroupElement],
+  ) -> Self {
     // Unoptimized.
     scalars
-      .into_iter()
-      .zip(points)
-      .map(|(scalar, point)| (*point.borrow()).mul(*scalar.borrow()))
+      .iter()
+      .zip(bases)
+      .map(|(scalar, base)| base.mul(scalar))
       .fold(Ep::group_zero(), |acc, x| acc + x)
   }
 
@@ -56,7 +50,7 @@ impl Group for pallas::Point {
     PallasCompressedElementWrapper::new(self.to_bytes())
   }
 
-  fn from_uniform_bytes(bytes: &[u8]) -> Option<Self> {
+  fn from_uniform_bytes(bytes: &[u8]) -> Option<Self::PreprocessedGroupElement> {
     if bytes.len() != 64 {
       None
     } else {
@@ -64,7 +58,7 @@ impl Group for pallas::Point {
       arr.copy_from_slice(&bytes[0..32]);
 
       let hash = Ep::hash_to_curve("from_uniform_bytes");
-      Some(hash(&arr))
+      Some(hash(&arr).to_affine())
     }
   }
 
@@ -121,27 +115,21 @@ impl VestaCompressedElementWrapper {
   }
 }
 
-unsafe impl Send for VestaCompressedElementWrapper {}
-unsafe impl Sync for VestaCompressedElementWrapper {}
-
 impl Group for vesta::Point {
   type Base = vesta::Base;
   type Scalar = vesta::Scalar;
   type CompressedGroupElement = VestaCompressedElementWrapper;
+  type PreprocessedGroupElement = vesta::Affine;
 
-  fn vartime_multiscalar_mul<I, J>(scalars: I, points: J) -> Self
-  where
-    I: IntoIterator,
-    I::Item: Borrow<Self::Scalar>,
-    J: IntoIterator,
-    J::Item: Borrow<Self>,
-    Self: Clone,
-  {
+  fn vartime_multiscalar_mul(
+    scalars: &[Self::Scalar],
+    bases: &[Self::PreprocessedGroupElement],
+  ) -> Self {
     // Unoptimized.
     scalars
-      .into_iter()
-      .zip(points)
-      .map(|(scalar, point)| (*point.borrow()).mul(*scalar.borrow()))
+      .iter()
+      .zip(bases)
+      .map(|(scalar, base)| base.mul(scalar))
       .fold(Eq::group_zero(), |acc, x| acc + x)
   }
 
@@ -149,7 +137,7 @@ impl Group for vesta::Point {
     VestaCompressedElementWrapper::new(self.to_bytes())
   }
 
-  fn from_uniform_bytes(bytes: &[u8]) -> Option<Self> {
+  fn from_uniform_bytes(bytes: &[u8]) -> Option<Self::PreprocessedGroupElement> {
     if bytes.len() != 64 {
       None
     } else {
@@ -157,7 +145,7 @@ impl Group for vesta::Point {
       arr.copy_from_slice(&bytes[0..32]);
 
       let hash = Eq::hash_to_curve("from_uniform_bytes");
-      Some(hash(&arr))
+      Some(hash(&arr).to_affine())
     }
   }
 

src/r1cs.rs

@@ -10,7 +10,6 @@ use itertools::concat;
 use rayon::prelude::*;
 
 /// Public parameters for a given R1CS
-#[derive(Debug)]
 pub struct R1CSGens<G: Group> {
   pub(crate) gens_W: CommitGens<G>, // TODO: avoid pub(crate)
   pub(crate) gens_E: CommitGens<G>,

src/traits.rs

@@ -1,7 +1,6 @@
 //! This module defines various traits required by the users of the library to implement.
 use bellperson::{gadgets::num::AllocatedNum, ConstraintSystem, SynthesisError};
 use core::{
-  borrow::Borrow,
   fmt::Debug,
   ops::{Add, AddAssign, Mul, MulAssign, Sub, SubAssign},
 };
@@ -30,21 +29,21 @@ pub trait Group:
   /// A type representing the compressed version of the group element
   type CompressedGroupElement: CompressedGroup<GroupElement = Self>;
 
+  /// A type representing preprocessed group element
+  type PreprocessedGroupElement;
+
   /// A method to compute a multiexponentation
-  fn vartime_multiscalar_mul<I, J>(scalars: I, points: J) -> Self
-  where
-    I: IntoIterator,
-    I::Item: Borrow<Self::Scalar>,
-    J: IntoIterator,
-    J::Item: Borrow<Self>,
-    Self: Clone;
+  fn vartime_multiscalar_mul(
+    scalars: &[Self::Scalar],
+    bases: &[Self::PreprocessedGroupElement],
+  ) -> Self;
 
   /// Compresses the group element
   fn compress(&self) -> Self::CompressedGroupElement;
 
   /// Attempts to create a group element from a sequence of bytes,
   /// failing with a `None` if the supplied bytes do not encode the group element
-  fn from_uniform_bytes(bytes: &[u8]) -> Option<Self>;
+  fn from_uniform_bytes(bytes: &[u8]) -> Option<Self::PreprocessedGroupElement>;
 
   /// Returns the affine coordinates (x, y, infinty) for the point
   fn to_coordinates(&self) -> (Self::Base, Self::Base, bool);