From 701e6cfa1bc2d5c2806d9050813444309e7c7a49 Mon Sep 17 00:00:00 2001
From: Jack Grigg <jack@z.cash>
Date: Sat, 6 Jun 2020 11:29:26 +1200
Subject: [PATCH] group: Make Wnaf generic over Group

Wnaf was originally generic over CurveProjective; in the prior refactor
commit, we renamed this to CofactorCurve. But w-NAF only requires scalar
multiplication, which is provided by the Group trait, so we relax the
bounds on Wnaf to enable it to be used with any group. We move the
generic w-NAF helper methods from the Curve trait to a new WnafGroup
extension trait, to keep the w-NAF API surface self-contained, and not
expose it to users who aren't using it.
---
 src/groth16/generator.rs          | 6 +++++-
 src/groth16/tests/dummy_engine.rs | 4 +++-
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/src/groth16/generator.rs b/src/groth16/generator.rs
index 084e7a3..d04ed6c 100644
--- a/src/groth16/generator.rs
+++ b/src/groth16/generator.rs
@@ -3,7 +3,7 @@ use std::ops::{AddAssign, MulAssign};
 use std::sync::Arc;
 
 use ff::{Field, PrimeField};
-use group::{cofactor::CofactorCurveAffine, Curve, Group, Wnaf};
+use group::{cofactor::CofactorCurveAffine, Curve, Group, Wnaf, WnafGroup};
 use pairing::Engine;
 
 use super::{Parameters, VerifyingKey};
@@ -22,6 +22,8 @@ pub fn generate_random_parameters<E, C, R>(
 ) -> Result<Parameters<E>, SynthesisError>
 where
     E: Engine,
+    E::G1: WnafGroup,
+    E::G2: WnafGroup,
     C: Circuit<E::Fr>,
     R: RngCore,
 {
@@ -165,6 +167,8 @@ pub fn generate_parameters<E, C>(
 ) -> Result<Parameters<E>, SynthesisError>
 where
     E: Engine,
+    E::G1: WnafGroup,
+    E::G2: WnafGroup,
     C: Circuit<E::Fr>,
 {
     let mut assembly = KeypairAssembly {
diff --git a/src/groth16/tests/dummy_engine.rs b/src/groth16/tests/dummy_engine.rs
index 17e0043..8f11fe1 100644
--- a/src/groth16/tests/dummy_engine.rs
+++ b/src/groth16/tests/dummy_engine.rs
@@ -2,7 +2,7 @@ use ff::{Field, PrimeField};
 use group::{
     cofactor::{CofactorCurve, CofactorCurveAffine, CofactorGroup},
     prime::PrimeGroup,
-    Curve, Group, GroupEncoding, UncompressedEncoding,
+    Curve, Group, GroupEncoding, UncompressedEncoding, WnafGroup,
 };
 use pairing::{Engine, MillerLoopResult, MultiMillerLoop, PairingCurveAffine};
 
@@ -414,7 +414,9 @@ impl Curve for Fr {
     fn to_affine(&self) -> Fr {
         *self
     }
+}
 
+impl WnafGroup for Fr {
     fn recommended_wnaf_for_scalar(_: &Self::Scalar) -> usize {
         3
     }