Use 2-NAF for representing ATE_LOOP_COUNT in MNT Miller loop (#96)

* 2-NAF for MNT pairings

* Apply suggestions from code review

* Apply suggestions from code review

* fix

* no std

* patch

* ci

Co-authored-by: Weikeng Chen <w.k@berkeley.edu>
Co-authored-by: onewayfunc <onewayfunc@gmail.com>

.github/workflows/ci.yml

@@ -187,6 +187,7 @@ jobs:
             echo "ark-ff = { git = 'https://github.com/arkworks-rs/algebra' }"
             echo "ark-poly = { git = 'https://github.com/arkworks-rs/algebra' }"
             echo "ark-serialize = { git = 'https://github.com/arkworks-rs/algebra' }"
+            echo "ark-algebra-bench-templates = { git = 'https://github.com/arkworks-rs/algebra' }"
             echo "ark-algebra-test-templates = { git = 'https://github.com/arkworks-rs/algebra' }"
             echo "ark-r1cs-std = { path = 'r1cs-std' }"
           } >> Cargo.toml

Cargo.toml

@@ -77,6 +77,7 @@ ark-std = { git = "https://github.com/arkworks-rs/std" }
 ark-ec = { git = "https://github.com/arkworks-rs/algebra" }
 ark-ff = { git = "https://github.com/arkworks-rs/algebra" }
 ark-poly = { git = "https://github.com/arkworks-rs/algebra" }
+ark-algebra-bench-templates = { git = "https://github.com/arkworks-rs/algebra" }
 ark-test-curves = { git = "https://github.com/arkworks-rs/algebra" }
 ark-bls12-381 = { git = "https://github.com/arkworks-rs/curves" }
 ark-bls12-377 = { git = "https://github.com/arkworks-rs/curves" }

src/groups/curves/short_weierstrass/bls12/mod.rs

@@ -43,7 +43,7 @@ impl G1PreparedVar
         let y = self.0.y.value()?;
         let infinity = self.0.infinity.value()?;
         let g = infinity
-            .then_some(GroupAffine::zero())
+            .then_some(GroupAffine::identity())
             .unwrap_or(GroupAffine::new(x, y))
             .into();
         Ok(g)

src/groups/curves/short_weierstrass/mnt4/mod.rs

@@ -291,33 +291,32 @@ impl G2PreparedVar
             t: Fp2G::<P>::one(),
         };
 
-        for (idx, value) in P::ATE_LOOP_COUNT.iter().rev().enumerate() {
-            let mut tmp = *value;
-            let skip_extraneous_bits = 64 - value.leading_zeros();
-            let mut v = Vec::with_capacity(16);
-            for i in 0..64 {
-                if idx == 0 && (i == 0 || i >= skip_extraneous_bits) {
-                    continue;
-                }
-                v.push(tmp & 1 == 1);
-                tmp >>= 1;
-            }
-
-            for bit in v.iter().rev() {
-                let (r2, coeff) = PairingVar::<P>::doubling_step_for_flipped_miller_loop(&r)?;
-                g2p.double_coefficients.push(coeff);
-                r = r2;
-
-                if *bit {
-                    let (r2, coeff) = PairingVar::<P>::mixed_addition_step_for_flipped_miller_loop(
-                        &q.x, &q.y, &r,
-                    )?;
-                    g2p.addition_coefficients.push(coeff);
-                    r = r2;
-                }
-
-                tmp >>= 1;
+        for bit in P::ATE_LOOP_COUNT.iter().skip(1) {
+            let (r2, coeff) = PairingVar::<P>::doubling_step_for_flipped_miller_loop(&r)?;
+            g2p.double_coefficients.push(coeff);
+            r = r2;
+
+            let add_coeff;
+            let r_temp;
+            match bit {
+                1 => {
+                    (r_temp, add_coeff) =
+                        PairingVar::<P>::mixed_addition_step_for_flipped_miller_loop(
+                            &q.x, &q.y, &r,
+                        )?;
+                },
+                -1 => {
+                    (r_temp, add_coeff) =
+                        PairingVar::<P>::mixed_addition_step_for_flipped_miller_loop(
+                            &q.x,
+                            &q.y.negate()?,
+                            &r,
+                        )?;
+                },
+                _ => continue,
             }
+            g2p.addition_coefficients.push(add_coeff);
+            r = r_temp;
         }
 
         if P::ATE_IS_LOOP_COUNT_NEG {

src/groups/curves/short_weierstrass/mnt6/mod.rs

@@ -291,33 +291,32 @@ impl G2PreparedVar
             t: Fp3G::<P>::one(),
         };
 
-        for (idx, value) in P::ATE_LOOP_COUNT.iter().rev().enumerate() {
-            let mut tmp = *value;
-            let skip_extraneous_bits = 64 - value.leading_zeros();
-            let mut v = Vec::with_capacity(16);
-            for i in 0..64 {
-                if idx == 0 && (i == 0 || i >= skip_extraneous_bits) {
-                    continue;
-                }
-                v.push(tmp & 1 == 1);
-                tmp >>= 1;
-            }
-
-            for bit in v.iter().rev() {
-                let (r2, coeff) = PairingVar::<P>::doubling_step_for_flipped_miller_loop(&r)?;
-                g2p.double_coefficients.push(coeff);
-                r = r2;
-
-                if *bit {
-                    let (r2, coeff) = PairingVar::<P>::mixed_addition_step_for_flipped_miller_loop(
-                        &q.x, &q.y, &r,
-                    )?;
-                    g2p.addition_coefficients.push(coeff);
-                    r = r2;
-                }
-
-                tmp >>= 1;
+        for bit in P::ATE_LOOP_COUNT.iter().skip(1) {
+            let (r2, coeff) = PairingVar::<P>::doubling_step_for_flipped_miller_loop(&r)?;
+            g2p.double_coefficients.push(coeff);
+            r = r2;
+
+            let add_coeff;
+            let r_temp;
+            match bit {
+                1 => {
+                    (r_temp, add_coeff) =
+                        PairingVar::<P>::mixed_addition_step_for_flipped_miller_loop(
+                            &q.x, &q.y, &r,
+                        )?;
+                },
+                -1 => {
+                    (r_temp, add_coeff) =
+                        PairingVar::<P>::mixed_addition_step_for_flipped_miller_loop(
+                            &q.x,
+                            &q.y.negate()?,
+                            &r,
+                        )?;
+                },
+                _ => continue,
             }
+            g2p.addition_coefficients.push(add_coeff);
+            r = r_temp;
         }
 
         if P::ATE_IS_LOOP_COUNT_NEG {

src/groups/curves/short_weierstrass/mod.rs

@@ -2,7 +2,7 @@ use ark_ec::{
     short_weierstrass::{
         Affine as SWAffine, Projective as SWProjective, SWCurveConfig as SWModelParameters,
     },
-    AffineCurve, ProjectiveCurve,
+    AffineRepr, CurveGroup,
 };
 use ark_ff::{BigInteger, BitIteratorBE, Field, One, PrimeField, Zero};
 use ark_relations::r1cs::{ConstraintSystemRef, Namespace, SynthesisError};
@@ -94,7 +94,7 @@ where
     /// constraint system.
     pub fn value(&self) -> Result<SWAffine<P>, SynthesisError> {
         Ok(match self.infinity.value()? {
-            true => SWAffine::zero(),
+            true => SWAffine::identity(),
             false => SWAffine::new(self.x.value()?, self.y.value()?),
         })
     }
@@ -137,7 +137,7 @@ where
         let result = if let Some(z_inv) = z.inverse() {
             SWAffine::new(x * &z_inv, y * &z_inv)
         } else {
-            SWAffine::zero()
+            SWAffine::identity()
         };
         Ok(result.into())
     }
@@ -209,7 +209,7 @@ where
         let (x, y, z) = match f() {
             Ok(ge) => {
                 let ge = ge.into_affine();
-                if ge.is_zero() {
+                if ge.is_identity() {
                     (
                         Ok(P::BaseField::zero()),
                         Ok(P::BaseField::one()),
@@ -782,7 +782,11 @@ where
         f: impl FnOnce() -> Result<T, SynthesisError>,
         mode: AllocationMode,
     ) -> Result<Self, SynthesisError> {
-        Self::new_variable(cs, || f().map(|b| b.borrow().into_projective()), mode)
+        Self::new_variable(
+            cs,
+            || f().map(|b| SWProjective::from((*b.borrow()).clone())),
+            mode,
+        )
     }
 }
 

src/groups/curves/short_weierstrass/non_zero_affine.rs

@@ -1,4 +1,6 @@
 use super::*;
+use ark_ec::Group;
+use ark_std::ops::Add;
 
 /// An affine representation of a prime order curve point that is guaranteed
 /// to *not* be the point at infinity.
@@ -43,8 +45,7 @@ where
     #[tracing::instrument(target = "r1cs", skip(self, other))]
     pub fn add_unchecked(&self, other: &Self) -> Result<Self, SynthesisError> {
         if [self, other].is_constant() {
-            let result =
-                (self.value()?.into_projective() + other.value()?.into_projective()).into_affine();
+            let result = self.value()?.add(other.value()?).into_affine();
             Ok(Self::new(F::constant(result.x), F::constant(result.y)))
         } else {
             let (x1, y1) = (&self.x, &self.y);
@@ -70,9 +71,11 @@ where
     #[tracing::instrument(target = "r1cs", skip(self))]
     pub fn double(&self) -> Result<Self, SynthesisError> {
         if [self].is_constant() {
-            let result = self.value()?.into_projective().double().into_affine();
+            let result = SWProjective::<P>::from(self.value()?)
+                .double()
+                .into_affine();
             // Panic if the result is zero.
-            assert!(!result.is_zero());
+            assert!(!result.is_identity());
             Ok(Self::new(F::constant(result.x), F::constant(result.y)))
         } else {
             let (x1, y1) = (&self.x, &self.y);
@@ -236,7 +239,7 @@ mod test_non_zero_affine {
         },
         R1CSVar,
     };
-    use ark_ec::{models::short_weierstrass::SWCurveConfig, ProjectiveCurve};
+    use ark_ec::{models::short_weierstrass::SWCurveConfig, CurveGroup};
     use ark_relations::r1cs::ConstraintSystem;
     use ark_std::{vec::Vec, One};
     use ark_test_curves::bls12_381::{g1::Parameters as G1Parameters, Fq};

src/groups/curves/twisted_edwards/mod.rs

@@ -3,10 +3,9 @@ use ark_ec::{
         Affine as TEAffine, MontCurveConfig as MontgomeryModelParameter,
         Projective as TEProjective, TECurveConfig as TEModelParameters,
     },
-    AffineCurve, ProjectiveCurve,
+    AffineRepr, CurveGroup, Group,
 };
 use ark_ff::{BigInteger, BitIteratorBE, Field, One, PrimeField, Zero};
-
 use ark_relations::r1cs::{ConstraintSystemRef, Namespace, SynthesisError};
 
 use crate::{prelude::*, ToConstraintFieldGadget, Vec};
@@ -85,7 +84,7 @@ mod montgomery_affine_impl {
             p: &TEAffine<P>,
         ) -> Result<(P::BaseField, P::BaseField), SynthesisError> {
             let montgomery_point: GroupAffine<P> = if p.y == P::BaseField::one() {
-                GroupAffine::zero()
+                GroupAffine::identity()
             } else if p.x == P::BaseField::zero() {
                 GroupAffine::new(P::BaseField::zero(), P::BaseField::zero())
             } else {
@@ -543,7 +542,7 @@ where
             if bits.len() == 2 {
                 let mut table = [multiples[0], multiples[1], multiples[0] + multiples[1]];
 
-                TEProjective::batch_normalization(&mut table);
+                TEProjective::normalize_batch(&mut table);
                 let x_s = [zero.x, table[0].x, table[1].x, table[2].x];
                 let y_s = [zero.y, table[0].y, table[1].y, table[2].y];
 
@@ -675,7 +674,11 @@ where
         f: impl FnOnce() -> Result<Point, SynthesisError>,
         mode: AllocationMode,
     ) -> Result<Self, SynthesisError> {
-        Self::new_variable(cs, || f().map(|b| b.borrow().into_projective()), mode)
+        Self::new_variable(
+            cs,
+            || f().map(|b| TEProjective::<P>::from((*b.borrow()).clone())),
+            mode,
+        )
     }
 }
 

src/groups/mod.rs

@@ -1,9 +1,9 @@
 use crate::prelude::*;
-use ark_ec::ProjectiveCurve;
 use ark_ff::Field;
 use ark_relations::r1cs::{Namespace, SynthesisError};
 use core::ops::{Add, AddAssign, Sub, SubAssign};
 
+use ark_ec::CurveGroup;
 use core::{borrow::Borrow, fmt::Debug};
 
 /// This module contains implementations of arithmetic for various curve models.
@@ -25,7 +25,7 @@ pub trait GroupOpsBounds<'a, F, T: 'a>:
 
 /// A variable that represents a curve point for
 /// the curve `C`.
-pub trait CurveVar<C: ProjectiveCurve, ConstraintF: Field>:
+pub trait CurveVar<C: CurveGroup, ConstraintF: Field>:
     'static
     + Sized
     + Clone

src/pairing/mnt4/mod.rs

@@ -10,7 +10,6 @@ use crate::{
     },
 };
 use ark_ec::mnt4::{MNT4Parameters, MNT4};
-use ark_ff::BitIteratorBE;
 
 use core::marker::PhantomData;
 
@@ -105,10 +104,8 @@ impl PairingVar
 
         // code below gets executed for all bits (EXCEPT the MSB itself) of
         // mnt6_param_p (skipping leading zeros) in MSB to LSB order
-        for (dbl_idx, bit) in BitIteratorBE::without_leading_zeros(P::ATE_LOOP_COUNT)
-            .skip(1)
-            .enumerate()
-        {
+        let y_over_twist_neg = &q.y_over_twist.negate()?;
+        for (dbl_idx, bit) in P::ATE_LOOP_COUNT.iter().skip(1).enumerate() {
             let dc = &q.double_coefficients[dbl_idx];
 
             let g_rr_at_p = Fp4G::<P>::new(
@@ -118,16 +115,29 @@ impl PairingVar
 
             f = f.square()? * &g_rr_at_p;
 
-            if bit {
+            let g_rq_at_p;
+            // Compute l_{R,Q}(P) if bit == 1, and l_{R,-Q}(P) if bit == -1
+            if *bit == 1 {
                 let ac = &q.addition_coefficients[add_idx];
                 add_idx += 1;
 
-                let g_rq_at_p = Fp4G::<P>::new(
+                g_rq_at_p = Fp4G::<P>::new(
                     &ac.c_rz * &p.y_twist,
                     (&q.y_over_twist * &ac.c_rz + &l1_coeff * &ac.c_l1).negate()?,
                 );
-                f *= &g_rq_at_p;
+            } else if *bit == -1 {
+                let ac = &q.addition_coefficients[add_idx];
+                add_idx += 1;
+
+                g_rq_at_p = Fp4G::<P>::new(
+                    &ac.c_rz * &p.y_twist,
+                    (y_over_twist_neg * &ac.c_rz + &l1_coeff * &ac.c_l1).negate()?,
+                );
+            } else {
+                continue;
             }
+
+            f *= &g_rq_at_p;
         }
 
         if P::ATE_IS_LOOP_COUNT_NEG {

src/pairing/mnt6/mod.rs

@@ -10,7 +10,6 @@ use crate::{
     },
 };
 use ark_ec::mnt6::{MNT6Parameters, MNT6};
-use ark_ff::fields::BitIteratorBE;
 use core::marker::PhantomData;
 
 /// Specifies the constraints for computing a pairing in a MNT6 bilinear group.
@@ -100,29 +99,40 @@ impl PairingVar
 
         // code below gets executed for all bits (EXCEPT the MSB itself) of
         // mnt6_param_p (skipping leading zeros) in MSB to LSB order
-        for (dbl_idx, bit) in BitIteratorBE::without_leading_zeros(P::ATE_LOOP_COUNT)
-            .skip(1)
-            .enumerate()
-        {
+        let y_over_twist_neg = &q.y_over_twist.negate()?;
+        for (dbl_idx, bit) in P::ATE_LOOP_COUNT.iter().skip(1).enumerate() {
             let dc = &q.double_coefficients[dbl_idx];
 
-            let g_rr_at_p = Fp6Var::new(
+            let g_rr_at_p = Fp6G::<P>::new(
                 &dc.c_l - &dc.c_4c - &dc.c_j * &p.x_twist,
                 &dc.c_h * &p.y_twist,
             );
 
             f = f.square()? * &g_rr_at_p;
 
-            if bit {
+            let g_rq_at_p;
+            // Compute l_{R,Q}(P) if bit == 1, and l_{R,-Q}(P) if bit == -1
+            if *bit == 1 {
                 let ac = &q.addition_coefficients[add_idx];
                 add_idx += 1;
 
-                let g_rq_at_p = Fp6Var::new(
+                g_rq_at_p = Fp6G::<P>::new(
                     &ac.c_rz * &p.y_twist,
-                    (&q.y_over_twist * &ac.c_rz + &(&l1_coeff * &ac.c_l1)).negate()?,
+                    (&q.y_over_twist * &ac.c_rz + &l1_coeff * &ac.c_l1).negate()?,
                 );
-                f *= &g_rq_at_p;
+            } else if *bit == -1 {
+                let ac = &q.addition_coefficients[add_idx];
+                add_idx += 1;
+
+                g_rq_at_p = Fp6G::<P>::new(
+                    &ac.c_rz * &p.y_twist,
+                    (y_over_twist_neg * &ac.c_rz + &l1_coeff * &ac.c_l1).negate()?,
+                );
+            } else {
+                continue;
             }
+
+            f *= &g_rq_at_p;
         }
 
         if P::ATE_IS_LOOP_COUNT_NEG {

src/pairing/mod.rs

@@ -1,5 +1,6 @@
 use crate::prelude::*;
-use ark_ec::PairingEngine;
+use ark_ec::pairing::Pairing;
+use ark_ec::CurveGroup;
 use ark_ff::Field;
 use ark_relations::r1cs::SynthesisError;
 use core::fmt::Debug;
@@ -13,22 +14,23 @@ pub mod mnt6;
 
 /// Specifies the constraints for computing a pairing in the yybilinear group
 /// `E`.
-pub trait PairingVar<E: PairingEngine, ConstraintF: Field = <E as PairingEngine>::Fq> {
+pub trait PairingVar<E: Pairing, ConstraintF: Field = <<E as Pairing>::G1 as CurveGroup>::BaseField>
+{
     /// An variable representing an element of `G1`.
     /// This is the R1CS equivalent of `E::G1Projective`.
-    type G1Var: CurveVar<E::G1Projective, ConstraintF>
-        + AllocVar<E::G1Projective, ConstraintF>
+    type G1Var: CurveVar<E::G1, ConstraintF>
+        + AllocVar<E::G1, ConstraintF>
         + AllocVar<E::G1Affine, ConstraintF>;
 
     /// An variable representing an element of `G2`.
     /// This is the R1CS equivalent of `E::G2Projective`.
-    type G2Var: CurveVar<E::G2Projective, ConstraintF>
-        + AllocVar<E::G2Projective, ConstraintF>
+    type G2Var: CurveVar<E::G2, ConstraintF>
+        + AllocVar<E::G2, ConstraintF>
         + AllocVar<E::G2Affine, ConstraintF>;
 
     /// An variable representing an element of `GT`.
     /// This is the R1CS equivalent of `E::GT`.
-    type GTVar: FieldVar<E::Fqk, ConstraintF>;
+    type GTVar: FieldVar<E::TargetField, ConstraintF>;
 
     /// An variable representing cached precomputation  that can speed up
     /// pairings computations. This is the R1CS equivalent of

tests/arithmetic_tests.rs

@@ -1,5 +1,5 @@
 use ark_bls12_381::Bls12_381;
-use ark_ec::PairingEngine;
+use ark_ec::{pairing::Pairing, CurveGroup};
 use ark_ff::{BigInteger, PrimeField};
 use ark_mnt4_298::MNT4_298;
 use ark_mnt4_753::MNT4_753;
@@ -673,48 +673,48 @@ macro_rules! nonnative_test {
 
 nonnative_test!(
     MNT46Small,
-    <MNT4_298 as PairingEngine>::Fr,
-    <MNT6_298 as PairingEngine>::Fr
+    <MNT4_298 as Pairing>::ScalarField,
+    <MNT6_298 as Pairing>::ScalarField
 );
 nonnative_test!(
     MNT64Small,
-    <MNT6_298 as PairingEngine>::Fr,
-    <MNT4_298 as PairingEngine>::Fr
+    <MNT6_298 as Pairing>::ScalarField,
+    <MNT4_298 as Pairing>::ScalarField
 );
 nonnative_test!(
     MNT46Big,
-    <MNT4_753 as PairingEngine>::Fr,
-    <MNT6_753 as PairingEngine>::Fr
+    <MNT4_753 as Pairing>::ScalarField,
+    <MNT6_753 as Pairing>::ScalarField
 );
 nonnative_test!(
     MNT64Big,
-    <MNT6_753 as PairingEngine>::Fr,
-    <MNT4_753 as PairingEngine>::Fr
+    <MNT6_753 as Pairing>::ScalarField,
+    <MNT4_753 as Pairing>::ScalarField
 );
 nonnative_test!(
     BLS12MNT4Small,
-    <Bls12_381 as PairingEngine>::Fr,
-    <MNT4_298 as PairingEngine>::Fr
+    <Bls12_381 as Pairing>::ScalarField,
+    <MNT4_298 as Pairing>::ScalarField
 );
 nonnative_test!(
     BLS12,
-    <Bls12_381 as PairingEngine>::Fq,
-    <Bls12_381 as PairingEngine>::Fr
+    <<Bls12_381 as Pairing>::G1 as CurveGroup>::BaseField,
+    <Bls12_381 as Pairing>::ScalarField
 );
 #[cfg(not(ci))]
 nonnative_test!(
     MNT6BigMNT4Small,
-    <MNT6_753 as PairingEngine>::Fr,
-    <MNT4_298 as PairingEngine>::Fr
+    <MNT6_753 as Pairing>::ScalarField,
+    <MNT4_298 as Pairing>::ScalarField
 );
 nonnative_test!(
     PallasFrMNT6Fr,
     ark_pallas::Fr,
-    <MNT6_753 as PairingEngine>::Fr
+    <MNT6_753 as Pairing>::ScalarField
 );
 nonnative_test!(
     MNT6FrPallasFr,
-    <MNT6_753 as PairingEngine>::Fr,
+    <MNT6_753 as Pairing>::ScalarField,
     ark_pallas::Fr
 );
 nonnative_test!(PallasFqFr, ark_pallas::Fq, ark_pallas::Fr);