Expose utilities (#35)

src/codec.rs

@@ -1,5 +1,5 @@
 use ark_ec::short_weierstrass::SWCurveConfig;
-use arkworks::te_sw_map;
+use utils::te_sw_map;
 
 use super::*;
 

src/lib.rs

@@ -32,12 +32,10 @@ pub mod utils;
 #[cfg(feature = "ring")]
 pub mod ring;
 
-#[allow(unused)]
-mod arkworks;
-
 #[cfg(test)]
 mod testing;
 
+// Re-export stuff that may be useful downstream
 pub mod prelude {
     pub use ark_ec;
     pub use ark_ff;

src/ring.rs

@@ -1,4 +1,4 @@
-use crate::arkworks::te_sw_map::SWMapping;
+use crate::utils::te_sw_map::SWMapping;
 use crate::*;
 use ark_ec::short_weierstrass::SWCurveConfig;
 use pedersen::{PedersenSuite, Proof as PedersenProof};

src/suites/bandersnatch.rs

@@ -48,7 +48,7 @@
 //!   with `h2c_suite_ID_string` = `"Bandersnatch_XMD:SHA-512_ELL2_RO_"`
 //!   and domain separation tag `DST = "ECVRF_" || h2c_suite_ID_string || suite_string`.
 
-use crate::{arkworks::te_sw_map::*, pedersen::PedersenSuite, *};
+use crate::{pedersen::PedersenSuite, utils::te_sw_map::*, *};
 use ark_ff::MontFp;
 
 pub mod weierstrass {
@@ -156,9 +156,7 @@ pub mod edwards {
         };
     }
 
-    impl arkworks::elligator2::Elligator2Config
-        for ark_ed_on_bls12_381_bandersnatch::BandersnatchConfig
-    {
+    impl utils::elligator2::Elligator2Config for ark_ed_on_bls12_381_bandersnatch::BandersnatchConfig {
         const Z: ark_ed_on_bls12_381_bandersnatch::Fq = MontFp!("5");
 
         /// This must be equal to 1/(MontCurveConfig::COEFF_B)^2;
@@ -234,17 +232,17 @@ impl MapConfig for ark_ed_on_bls12_381_bandersnatch::BandersnatchConfig {
 
 #[cfg(test)]
 mod tests {
-    use crate::{testing, utils::te_sw_map::*};
+    use crate::{testing, utils::*};
     use ark_ed_on_bls12_381_bandersnatch::{BandersnatchConfig, SWAffine};
 
     #[test]
     fn sw_to_te_roundtrip() {
         let org_point = testing::random_val::<SWAffine>(None);
 
-        let te_point = map_sw_to_te::<BandersnatchConfig>(&org_point).unwrap();
+        let te_point = sw_to_te::<BandersnatchConfig>(&org_point).unwrap();
         assert!(te_point.is_on_curve());
 
-        let sw_point = map_te_to_sw::<BandersnatchConfig>(&te_point).unwrap();
+        let sw_point = te_to_sw::<BandersnatchConfig>(&te_point).unwrap();
         assert!(sw_point.is_on_curve());
 
         assert_eq!(org_point, sw_point);
@@ -404,3 +402,54 @@ mod test_vectors_ring_sw {
         testing::test_vectors_process::<V>(VECTOR_ID);
     }
 }
+
+#[test]
+fn blinding_base_sw_te_rountrip() {
+    use crate::utils::*;
+    let sw = weierstrass::BandersnatchSha512Tai::BLINDING_BASE;
+    let ed = sw_to_te(&sw).unwrap();
+    assert_eq!(ed, edwards::BandersnatchSha512Ell2::BLINDING_BASE);
+    let sw2 = te_to_sw(&ed).unwrap();
+    assert_eq!(sw, sw2);
+}
+
+#[cfg(all(test, feature = "ring"))]
+#[test]
+fn accumulator_base_sw_te_roundtrip() {
+    use crate::{ring::RingSuite, utils::*};
+    let sw = weierstrass::BandersnatchSha512Tai::ACCUMULATOR_BASE;
+    let ed = sw_to_te(&sw).unwrap();
+    assert_eq!(ed, edwards::BandersnatchSha512Ell2::ACCUMULATOR_BASE);
+    let sw2 = te_to_sw(&ed).unwrap();
+    assert_eq!(sw, sw2);
+}
+
+#[cfg(all(test, feature = "ring"))]
+#[test]
+fn padding_point_sw_te_roundtrip() {
+    use crate::utils::*;
+    // Fixed padding point
+    let sw = {
+        const X: weierstrass::BaseField = MontFp!(
+            "25448400713078632486748382313960039031302935774474538965225823993599751298535"
+        );
+        const Y: weierstrass::BaseField = MontFp!(
+            "24382892199244280513693545286348030912870264650402775682704689602954457435722"
+        );
+        weierstrass::AffinePoint::new_unchecked(X, Y)
+    };
+    let ed = sw_to_te(&sw).unwrap();
+    let sw2 = te_to_sw(&ed).unwrap();
+    assert_eq!(sw, sw2);
+}
+
+#[test]
+fn generator_roundtrip() {
+    use crate::utils::*;
+    let sw1 = weierstrass::AffinePoint::generator();
+    let ed1 = sw_to_te(&sw1).unwrap();
+    let ed2 = edwards::AffinePoint::generator();
+    assert_eq!(ed1, ed2);
+    let sw2 = te_to_sw(&ed1).unwrap();
+    assert_eq!(sw1, sw2);
+}

src/utils.rs → src/utils/common.rs

@@ -1,50 +1,20 @@
 use crate::*;
 
-#[allow(unused)]
-pub(crate) use crate::arkworks::{elligator2, te_sw_map};
-
 use ark_ec::AffineRepr;
 use ark_ff::PrimeField;
 use digest::{Digest, FixedOutputReset};
 
 #[cfg(not(feature = "std"))]
 use ark_std::vec::Vec;
 
-#[macro_export]
-macro_rules! suite_types {
-    ($suite:ident) => {
-        #[allow(dead_code)]
-        pub type Secret = $crate::Secret<$suite>;
-        #[allow(dead_code)]
-        pub type Public = $crate::Public<$suite>;
-        #[allow(dead_code)]
-        pub type Input = $crate::Input<$suite>;
-        #[allow(dead_code)]
-        pub type Output = $crate::Output<$suite>;
-        #[allow(dead_code)]
-        pub type AffinePoint = $crate::AffinePoint<$suite>;
-        #[allow(dead_code)]
-        pub type ScalarField = $crate::ScalarField<$suite>;
-        #[allow(dead_code)]
-        pub type BaseField = $crate::BaseField<$suite>;
-        #[allow(dead_code)]
-        pub type IetfProof = $crate::ietf::Proof<$suite>;
-        #[allow(dead_code)]
-        pub type PedersenProof = $crate::pedersen::Proof<$suite>;
-        #[cfg(feature = "ring")]
-        #[allow(dead_code)]
-        pub type RingProof = $crate::ring::Proof<$suite>;
-    };
-}
-
 // Generic hash wrapper.
 pub(crate) fn hash<H: Digest>(data: &[u8]) -> digest::Output<H> {
     H::new().chain_update(data).finalize()
 }
 
 /// Generic HMAC wrapper.
 #[cfg(feature = "rfc-6979")]
-pub(crate) fn hmac<H: Digest + digest::core_api::BlockSizeUser>(sk: &[u8], data: &[u8]) -> Vec<u8> {
+fn hmac<H: Digest + digest::core_api::BlockSizeUser>(sk: &[u8], data: &[u8]) -> Vec<u8> {
     use hmac::{Mac, SimpleHmac};
     SimpleHmac::<H>::new_from_slice(sk)
         .expect("HMAC can take key of any size")
@@ -115,15 +85,16 @@ pub fn hash_to_curve_tai_rfc_9381<S: Suite>(data: &[u8]) -> Option<AffinePoint<S
 /// is given by the h2c_suite_ID_string parameter.
 ///
 /// The input `data` is defined to be `salt || alpha` according to the RFC 9281.
+#[allow(unused)]
 pub fn hash_to_curve_ell2_rfc_9380<S: Suite>(
     data: &[u8],
     h2c_suite_id: &[u8],
 ) -> Option<AffinePoint<S>>
 where
     <S as Suite>::Hasher: Default + Clone + FixedOutputReset + 'static,
     crate::CurveConfig<S>: ark_ec::twisted_edwards::TECurveConfig,
-    crate::CurveConfig<S>: crate::arkworks::elligator2::Elligator2Config,
-    crate::arkworks::elligator2::Elligator2Map<crate::CurveConfig<S>>:
+    crate::CurveConfig<S>: crate::utils::elligator2::Elligator2Config,
+    crate::utils::elligator2::Elligator2Map<crate::CurveConfig<S>>:
         ark_ec::hashing::map_to_curve_hasher::MapToCurve<<AffinePoint<S> as AffineRepr>::Group>,
 {
     use ark_ec::hashing::HashToCurve;
@@ -140,7 +111,7 @@ where
     let hasher = ark_ec::hashing::map_to_curve_hasher::MapToCurveBasedHasher::<
         <AffinePoint<S> as AffineRepr>::Group,
         ark_ff::field_hashers::DefaultFieldHasher<<S as Suite>::Hasher, SEC_PARAM>,
-        crate::arkworks::elligator2::Elligator2Map<crate::CurveConfig<S>>,
+        crate::utils::elligator2::Elligator2Map<crate::CurveConfig<S>>,
     >::new(&dst)
     .ok()?;
 

src/arkworks/elligator2.rs → src/utils/elligator2.rs

@@ -1,8 +1,11 @@
-//! Elligator2 has been merged upstream, still we're waiting for new version on crates.io (v.0.4.3)
+//! Elligator2 has been merged into arkworks upstream, still we're waiting
+//! for new version on crates.io (v.0.4.3)
 //!
 //! Relevant PRs:
 //! - Elligator2 hash-to-curve for Twisted Edwards curves: https://github.com/arkworks-rs/algebra/pull/659
 //! - Elligator2 hash-to-curve for Bandersnatch: https://github.com/arkworks-rs/algebra/pull/758
+//!
+//! This is mostly a verbatim copy of such PRs contribution.
 
 use ark_ec::{
     hashing::{curve_maps::swu::parity, map_to_curve_hasher::MapToCurve, HashToCurveError},

src/utils/mod.rs

@@ -0,0 +1,39 @@
+//! Features expected to land into Arkworks at some point in the future
+
+/// Elligator 2 hash-to-curve.
+pub(crate) mod elligator2;
+/// Twisted Edwards to Short Weierstrass mapping.
+pub(crate) mod te_sw_map;
+// Common utilities
+pub(crate) mod common;
+
+pub(crate) use common::*;
+
+pub use te_sw_map::{sw_to_te, te_to_sw, SWMapping};
+
+#[macro_export]
+macro_rules! suite_types {
+    ($suite:ident) => {
+        #[allow(dead_code)]
+        pub type Secret = $crate::Secret<$suite>;
+        #[allow(dead_code)]
+        pub type Public = $crate::Public<$suite>;
+        #[allow(dead_code)]
+        pub type Input = $crate::Input<$suite>;
+        #[allow(dead_code)]
+        pub type Output = $crate::Output<$suite>;
+        #[allow(dead_code)]
+        pub type AffinePoint = $crate::AffinePoint<$suite>;
+        #[allow(dead_code)]
+        pub type ScalarField = $crate::ScalarField<$suite>;
+        #[allow(dead_code)]
+        pub type BaseField = $crate::BaseField<$suite>;
+        #[allow(dead_code)]
+        pub type IetfProof = $crate::ietf::Proof<$suite>;
+        #[allow(dead_code)]
+        pub type PedersenProof = $crate::pedersen::Proof<$suite>;
+        #[cfg(feature = "ring")]
+        #[allow(dead_code)]
+        pub type RingProof = $crate::ring::Proof<$suite>;
+    };
+}

src/arkworks/te_sw_map.rs → src/utils/te_sw_map.rs

@@ -1,4 +1,3 @@
-use crate::*;
 use ark_ec::{
     short_weierstrass::{Affine as WeierstrassAffine, SWCurveConfig},
     twisted_edwards::{Affine as EdwardsAffine, MontCurveConfig, TECurveConfig},
@@ -13,7 +12,8 @@ pub trait MapConfig: TECurveConfig + SWCurveConfig + MontCurveConfig {
     const MONT_B_INV: <Self as CurveConfig>::BaseField;
 }
 
-pub fn map_sw_to_te<C: MapConfig>(point: &WeierstrassAffine<C>) -> Option<EdwardsAffine<C>> {
+/// Map a a point in Short Weierstrass form into its corresponding point in Twisted Edwards form.
+pub fn sw_to_te<C: MapConfig>(point: &WeierstrassAffine<C>) -> Option<EdwardsAffine<C>> {
     // First map the point from SW to Montgomery
     // (Bx - A/3, By)
     let mx = <C as MontCurveConfig>::COEFF_B * point.x - C::MONT_A_OVER_THREE;
@@ -30,7 +30,8 @@ pub fn map_sw_to_te<C: MapConfig>(point: &WeierstrassAffine<C>) -> Option<Edward
     Some(EdwardsAffine::new_unchecked(v, w))
 }
 
-pub fn map_te_to_sw<C: MapConfig>(point: &EdwardsAffine<C>) -> Option<WeierstrassAffine<C>> {
+/// Map a a point in Twisted Edwards form into its corresponding point in Short Weierstrass form.
+pub fn te_to_sw<C: MapConfig>(point: &EdwardsAffine<C>) -> Option<WeierstrassAffine<C>> {
     // Map from TE to Montgomery: (1+y)/(1-y), (1+y)/(x(1-y))
     let v_denom = <<C as CurveConfig>::BaseField as One>::one() - point.y;
     let w_denom = point.x - point.x * point.y;
@@ -79,14 +80,14 @@ impl<C: MapConfig> SWMapping<C> for EdwardsAffine<C> {
     fn from_sw(sw: WeierstrassAffine<C>) -> Self {
         const ERR_MSG: &str =
             "SW to TE is expected to be implemented only for curves supporting the mapping";
-        map_sw_to_te(&sw).expect(ERR_MSG)
+        sw_to_te(&sw).expect(ERR_MSG)
     }
 
     #[inline(always)]
     fn into_sw(self) -> WeierstrassAffine<C> {
         const ERR_MSG: &str =
             "TE to SW is expected to be implemented only for curves supporting the mapping";
-        map_te_to_sw(&self).expect(ERR_MSG)
+        te_to_sw(&self).expect(ERR_MSG)
     }
 
     #[inline(always)]