group: Move uncompressed encodings to an UncompressedEncoding trait
Specifications of deployed elliptic curves fall into one of two categories: - They specify both compressed and uncompressed encodings, allowing implementations to use either depending on performance vs data size considerations. - They specify a single point encoding format using point compression. I am unaware of any elliptic curve specification that explicitly forbids compressed encodings. To support both categories of elliptic curves, we provide the CurveAffine::Compressed associated type which all curves must define, and then curves that additionally specify an uncompressed encoding may implement the UncompressedEncoding trait and its Uncompressed associated type. pairing::PairingCurveAffine continues to require that its groups provide uncompressed encodings, because this is relied upon by bellman::groth16. We can revisit this restriction when that module is refactored as a separate crate.
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@ -2,7 +2,7 @@
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//!
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//! [Groth16]: https://eprint.iacr.org/2016/260
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use group::CurveAffine;
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use group::{CurveAffine, UncompressedEncoding};
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use pairing::{Engine, MultiMillerLoop};
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use crate::SynthesisError;
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@ -158,7 +158,7 @@ impl<E: Engine> VerifyingKey<E> {
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pub fn read<R: Read>(mut reader: R) -> io::Result<Self> {
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let read_g1 = |reader: &mut R| -> io::Result<E::G1Affine> {
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let mut g1_repr = <E::G1Affine as CurveAffine>::Uncompressed::default();
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let mut g1_repr = <E::G1Affine as UncompressedEncoding>::Uncompressed::default();
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reader.read_exact(g1_repr.as_mut())?;
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let affine = E::G1Affine::from_uncompressed(&g1_repr);
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@ -170,7 +170,7 @@ impl<E: Engine> VerifyingKey<E> {
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};
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let read_g2 = |reader: &mut R| -> io::Result<E::G2Affine> {
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let mut g2_repr = <E::G2Affine as CurveAffine>::Uncompressed::default();
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let mut g2_repr = <E::G2Affine as UncompressedEncoding>::Uncompressed::default();
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reader.read_exact(g2_repr.as_mut())?;
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let affine = E::G2Affine::from_uncompressed(&g2_repr);
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@ -289,7 +289,7 @@ impl<E: Engine> Parameters<E> {
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pub fn read<R: Read>(mut reader: R, checked: bool) -> io::Result<Self> {
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let read_g1 = |reader: &mut R| -> io::Result<E::G1Affine> {
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let mut repr = <E::G1Affine as CurveAffine>::Uncompressed::default();
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let mut repr = <E::G1Affine as UncompressedEncoding>::Uncompressed::default();
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reader.read_exact(repr.as_mut())?;
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let affine = if checked {
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@ -317,7 +317,7 @@ impl<E: Engine> Parameters<E> {
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};
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let read_g2 = |reader: &mut R| -> io::Result<E::G2Affine> {
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let mut repr = <E::G2Affine as CurveAffine>::Uncompressed::default();
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let mut repr = <E::G2Affine as UncompressedEncoding>::Uncompressed::default();
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reader.read_exact(repr.as_mut())?;
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let affine = if checked {
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@ -1,5 +1,5 @@
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use ff::{Field, PrimeField};
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use group::{CurveAffine, CurveProjective, Group, PrimeGroup};
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use group::{CurveAffine, CurveProjective, Group, PrimeGroup, UncompressedEncoding};
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use pairing::{Engine, MillerLoopResult, MultiMillerLoop, PairingCurveAffine};
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use rand_core::RngCore;
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@ -434,7 +434,6 @@ impl AsRef<[u8]> for FakePoint {
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impl CurveAffine for Fr {
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type Compressed = FakePoint;
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type Uncompressed = FakePoint;
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type Projective = Fr;
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type Scalar = Fr;
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@ -465,6 +464,10 @@ impl CurveAffine for Fr {
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fn to_compressed(&self) -> Self::Compressed {
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unimplemented!()
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}
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}
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impl UncompressedEncoding for Fr {
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type Uncompressed = FakePoint;
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fn from_uncompressed(_bytes: &Self::Uncompressed) -> CtOption<Self> {
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unimplemented!()
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@ -132,7 +132,6 @@ pub trait CurveAffine:
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{
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type Scalar: PrimeField;
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type Projective: CurveProjective<Affine = Self, Scalar = Self::Scalar>;
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type Uncompressed: Default + AsRef<[u8]> + AsMut<[u8]>;
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type Compressed: Default + AsRef<[u8]> + AsMut<[u8]>;
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/// Returns the additive identity.
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@ -162,6 +161,12 @@ pub trait CurveAffine:
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/// Converts this element into its compressed encoding, so long as it's not
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/// the point at infinity.
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fn to_compressed(&self) -> Self::Compressed;
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}
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/// Affine representation of a point on an elliptic curve that has a defined uncompressed
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/// encoding.
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pub trait UncompressedEncoding: CurveAffine {
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type Uncompressed: Default + AsRef<[u8]> + AsMut<[u8]>;
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/// Attempts to deserialize an element from its uncompressed encoding.
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fn from_uncompressed(bytes: &Self::Uncompressed) -> CtOption<Self>;
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@ -171,7 +176,7 @@ pub trait CurveAffine:
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///
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/// **This is dangerous to call unless you trust the bytes you are reading; otherwise,
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/// API invariants may be broken.** Please consider using
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/// [`CurveAffine::from_uncompressed`] instead.
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/// [`UncompressedEncoding::from_uncompressed`] instead.
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fn from_uncompressed_unchecked(bytes: &Self::Uncompressed) -> CtOption<Self>;
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/// Converts this element into its uncompressed encoding, so long as it's not
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@ -3,7 +3,7 @@ use rand::SeedableRng;
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use rand_xorshift::XorShiftRng;
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use std::ops::{Mul, Neg};
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use crate::{CurveAffine, CurveProjective};
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use crate::{CurveAffine, CurveProjective, UncompressedEncoding};
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pub fn curve_tests<G: CurveProjective>() {
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let mut rng = XorShiftRng::from_seed([
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@ -62,7 +62,7 @@ pub fn curve_tests<G: CurveProjective>() {
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random_negation_tests::<G>();
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random_transformation_tests::<G>();
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random_wnaf_tests::<G>();
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random_encoding_tests::<G>();
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random_compressed_encoding_tests::<G>();
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}
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fn random_wnaf_tests<G: CurveProjective>() {
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@ -394,17 +394,12 @@ fn random_transformation_tests<G: CurveProjective>() {
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}
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}
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fn random_encoding_tests<G: CurveProjective>() {
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fn random_compressed_encoding_tests<G: CurveProjective>() {
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let mut rng = XorShiftRng::from_seed([
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0x59, 0x62, 0xbe, 0x5d, 0x76, 0x3d, 0x31, 0x8d, 0x17, 0xdb, 0x37, 0x32, 0x54, 0x06, 0xbc,
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0xe5,
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]);
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assert_eq!(
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G::Affine::from_uncompressed(&G::Affine::identity().to_uncompressed()).unwrap(),
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G::Affine::identity()
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);
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assert_eq!(
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G::Affine::from_compressed(&G::Affine::identity().to_compressed()).unwrap(),
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G::Affine::identity()
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@ -413,10 +408,6 @@ fn random_encoding_tests<G: CurveProjective>() {
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for _ in 0..1000 {
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let mut r = G::random(&mut rng).to_affine();
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let uncompressed = r.to_uncompressed();
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let de_uncompressed = G::Affine::from_uncompressed(&uncompressed).unwrap();
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assert_eq!(de_uncompressed, r);
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let compressed = r.to_compressed();
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let de_compressed = G::Affine::from_compressed(&compressed).unwrap();
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assert_eq!(de_compressed, r);
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@ -428,3 +419,26 @@ fn random_encoding_tests<G: CurveProjective>() {
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assert_eq!(de_compressed, r);
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}
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}
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pub fn random_uncompressed_encoding_tests<G: CurveProjective>()
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where
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G::Affine: UncompressedEncoding,
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{
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let mut rng = XorShiftRng::from_seed([
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0x59, 0x62, 0xbe, 0x5d, 0x76, 0x3d, 0x31, 0x8d, 0x17, 0xdb, 0x37, 0x32, 0x54, 0x06, 0xbc,
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0xe5,
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]);
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assert_eq!(
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G::Affine::from_uncompressed(&G::Affine::identity().to_uncompressed()).unwrap(),
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G::Affine::identity()
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);
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for _ in 0..1000 {
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let r = G::random(&mut rng).to_affine();
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let uncompressed = r.to_uncompressed();
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let de_uncompressed = G::Affine::from_uncompressed(&uncompressed).unwrap();
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assert_eq!(de_uncompressed, r);
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}
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}
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@ -200,7 +200,6 @@ macro_rules! curve_impl {
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impl CurveAffine for $affine {
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type Scalar = $scalarfield;
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type Projective = $projective;
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type Uncompressed = $uncompressed;
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type Compressed = $compressed;
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fn identity() -> Self {
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@ -248,6 +247,10 @@ macro_rules! curve_impl {
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fn to_compressed(&self) -> Self::Compressed {
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$compressed::from_affine(*self)
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}
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}
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impl UncompressedEncoding for $affine {
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type Uncompressed = $uncompressed;
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fn from_uncompressed(bytes: &Self::Uncompressed) -> CtOption<Self> {
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Self::from_uncompressed_unchecked(bytes).and_then(|affine| {
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@ -901,7 +904,7 @@ pub mod g1 {
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use super::{g2::G2Affine, GroupDecodingError};
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use crate::{Engine, PairingCurveAffine};
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use ff::{BitIterator, Field, PrimeField};
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use group::{CurveAffine, CurveProjective, Group, PrimeGroup};
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use group::{CurveAffine, CurveProjective, Group, PrimeGroup, UncompressedEncoding};
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use rand_core::RngCore;
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use std::fmt;
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use std::ops::{AddAssign, MulAssign, Neg, SubAssign};
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@ -1467,8 +1470,9 @@ pub mod g1 {
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#[test]
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fn g1_curve_tests() {
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use group::tests::curve_tests;
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use group::tests::{curve_tests, random_uncompressed_encoding_tests};
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curve_tests::<G1>();
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random_uncompressed_encoding_tests::<G1>();
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}
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}
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@ -1477,7 +1481,7 @@ pub mod g2 {
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use super::{g1::G1Affine, GroupDecodingError};
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use crate::{Engine, PairingCurveAffine};
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use ff::{BitIterator, Field, PrimeField};
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use group::{CurveAffine, CurveProjective, Group, PrimeGroup};
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use group::{CurveAffine, CurveProjective, Group, PrimeGroup, UncompressedEncoding};
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use rand_core::RngCore;
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use std::fmt;
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use std::ops::{AddAssign, MulAssign, Neg, SubAssign};
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@ -2167,8 +2171,9 @@ pub mod g2 {
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#[test]
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fn g2_curve_tests() {
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use group::tests::curve_tests;
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use group::tests::{curve_tests, random_uncompressed_encoding_tests};
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curve_tests::<G2>();
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random_uncompressed_encoding_tests::<G2>();
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}
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}
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@ -1,5 +1,5 @@
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use ff::PrimeField;
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use group::{CurveAffine, CurveProjective};
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use group::{CurveAffine, CurveProjective, UncompressedEncoding};
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use super::*;
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use crate::*;
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@ -55,9 +55,12 @@ fn test_pairing_result_against_relic() {
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});
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}
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fn uncompressed_test_vectors<G: CurveProjective>(expected: &[u8]) {
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fn uncompressed_test_vectors<G: CurveProjective>(expected: &[u8])
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where
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G::Affine: UncompressedEncoding,
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{
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let mut e = G::identity();
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let encoded_len = <G::Affine as CurveAffine>::Uncompressed::default()
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let encoded_len = <G::Affine as UncompressedEncoding>::Uncompressed::default()
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.as_ref()
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.len();
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@ -69,7 +72,7 @@ fn uncompressed_test_vectors<G: CurveProjective>(expected: &[u8]) {
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let encoded = e_affine.to_uncompressed();
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v.extend_from_slice(encoded.as_ref());
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let mut decoded = <G::Affine as CurveAffine>::Uncompressed::default();
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let mut decoded = <G::Affine as UncompressedEncoding>::Uncompressed::default();
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decoded.as_mut().copy_from_slice(&expected[0..encoded_len]);
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expected = &expected[encoded_len..];
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let decoded = G::Affine::from_uncompressed(&decoded).unwrap();
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@ -22,7 +22,10 @@ pub mod bls12_381;
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use core::ops::Mul;
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use ff::{Field, PrimeField};
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use group::{CurveAffine, CurveProjective, GroupOps, GroupOpsOwned, ScalarMul, ScalarMulOwned};
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use group::{
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CurveAffine, CurveProjective, GroupOps, GroupOpsOwned, ScalarMul, ScalarMulOwned,
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UncompressedEncoding,
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};
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/// An "engine" is a collection of types (fields, elliptic curve groups, etc.)
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/// with well-defined relationships. In particular, the G1/G2 curve groups are
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@ -77,7 +80,7 @@ pub trait Engine: Sized + 'static + Clone {
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/// Affine representation of an elliptic curve point that can be used
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/// to perform pairings.
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pub trait PairingCurveAffine: CurveAffine {
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pub trait PairingCurveAffine: CurveAffine + UncompressedEncoding {
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type Pair: PairingCurveAffine<Pair = Self>;
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type PairingResult: Field;
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