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Diffstat (limited to 'vendor/elliptic-curve/src/point/non_identity.rs')
| -rw-r--r-- | vendor/elliptic-curve/src/point/non_identity.rs | 237 |
1 files changed, 237 insertions, 0 deletions
diff --git a/vendor/elliptic-curve/src/point/non_identity.rs b/vendor/elliptic-curve/src/point/non_identity.rs new file mode 100644 index 0000000..81c31cd --- /dev/null +++ b/vendor/elliptic-curve/src/point/non_identity.rs @@ -0,0 +1,237 @@ +//! Non-identity point type. + +use core::ops::{Deref, Mul}; + +use group::{prime::PrimeCurveAffine, Curve, GroupEncoding}; +use rand_core::{CryptoRng, RngCore}; +use subtle::{Choice, ConditionallySelectable, ConstantTimeEq, CtOption}; + +#[cfg(feature = "serde")] +use serdect::serde::{de, ser, Deserialize, Serialize}; + +use crate::{CurveArithmetic, NonZeroScalar, Scalar}; + +/// Non-identity point type. +/// +/// This type ensures that its value is not the identity point, ala `core::num::NonZero*`. +/// +/// In the context of ECC, it's useful for ensuring that certain arithmetic +/// cannot result in the identity point. +#[derive(Clone, Copy)] +pub struct NonIdentity<P> { + point: P, +} + +impl<P> NonIdentity<P> +where + P: ConditionallySelectable + ConstantTimeEq + Default, +{ + /// Create a [`NonIdentity`] from a point. + pub fn new(point: P) -> CtOption<Self> { + CtOption::new(Self { point }, !point.ct_eq(&P::default())) + } + + pub(crate) fn new_unchecked(point: P) -> Self { + Self { point } + } +} + +impl<P> NonIdentity<P> +where + P: ConditionallySelectable + ConstantTimeEq + Default + GroupEncoding, +{ + /// Decode a [`NonIdentity`] from its encoding. + pub fn from_repr(repr: &P::Repr) -> CtOption<Self> { + Self::from_bytes(repr) + } +} + +impl<P: Copy> NonIdentity<P> { + /// Return wrapped point. + pub fn to_point(self) -> P { + self.point + } +} + +impl<P> NonIdentity<P> +where + P: ConditionallySelectable + ConstantTimeEq + Curve + Default, +{ + /// Generate a random `NonIdentity<ProjectivePoint>`. + pub fn random(mut rng: impl CryptoRng + RngCore) -> Self { + loop { + if let Some(point) = Self::new(P::random(&mut rng)).into() { + break point; + } + } + } + + /// Converts this element into its affine representation. + pub fn to_affine(self) -> NonIdentity<P::AffineRepr> { + NonIdentity { + point: self.point.to_affine(), + } + } +} + +impl<P> NonIdentity<P> +where + P: PrimeCurveAffine, +{ + /// Converts this element to its curve representation. + pub fn to_curve(self) -> NonIdentity<P::Curve> { + NonIdentity { + point: self.point.to_curve(), + } + } +} + +impl<P> AsRef<P> for NonIdentity<P> { + fn as_ref(&self) -> &P { + &self.point + } +} + +impl<P> ConditionallySelectable for NonIdentity<P> +where + P: ConditionallySelectable, +{ + fn conditional_select(a: &Self, b: &Self, choice: Choice) -> Self { + Self { + point: P::conditional_select(&a.point, &b.point, choice), + } + } +} + +impl<P> ConstantTimeEq for NonIdentity<P> +where + P: ConstantTimeEq, +{ + fn ct_eq(&self, other: &Self) -> Choice { + self.point.ct_eq(&other.point) + } +} + +impl<P> Deref for NonIdentity<P> { + type Target = P; + + fn deref(&self) -> &Self::Target { + &self.point + } +} + +impl<P> GroupEncoding for NonIdentity<P> +where + P: ConditionallySelectable + ConstantTimeEq + Default + GroupEncoding, +{ + type Repr = P::Repr; + + fn from_bytes(bytes: &Self::Repr) -> CtOption<Self> { + let point = P::from_bytes(bytes); + point.and_then(|point| CtOption::new(Self { point }, !point.ct_eq(&P::default()))) + } + + fn from_bytes_unchecked(bytes: &Self::Repr) -> CtOption<Self> { + P::from_bytes_unchecked(bytes).map(|point| Self { point }) + } + + fn to_bytes(&self) -> Self::Repr { + self.point.to_bytes() + } +} + +impl<C, P> Mul<NonZeroScalar<C>> for NonIdentity<P> +where + C: CurveArithmetic, + P: Copy + Mul<Scalar<C>, Output = P>, +{ + type Output = NonIdentity<P>; + + fn mul(self, rhs: NonZeroScalar<C>) -> Self::Output { + &self * &rhs + } +} + +impl<C, P> Mul<&NonZeroScalar<C>> for &NonIdentity<P> +where + C: CurveArithmetic, + P: Copy + Mul<Scalar<C>, Output = P>, +{ + type Output = NonIdentity<P>; + + fn mul(self, rhs: &NonZeroScalar<C>) -> Self::Output { + NonIdentity { + point: self.point * *rhs.as_ref(), + } + } +} + +#[cfg(feature = "serde")] +impl<P> Serialize for NonIdentity<P> +where + P: Serialize, +{ + fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error> + where + S: ser::Serializer, + { + self.point.serialize(serializer) + } +} + +#[cfg(feature = "serde")] +impl<'de, P> Deserialize<'de> for NonIdentity<P> +where + P: ConditionallySelectable + ConstantTimeEq + Default + Deserialize<'de> + GroupEncoding, +{ + fn deserialize<D>(deserializer: D) -> Result<Self, D::Error> + where + D: de::Deserializer<'de>, + { + Option::from(Self::new(P::deserialize(deserializer)?)) + .ok_or_else(|| de::Error::custom("expected non-identity point")) + } +} + +#[cfg(all(test, feature = "dev"))] +mod tests { + use super::NonIdentity; + use crate::dev::{AffinePoint, ProjectivePoint}; + use group::GroupEncoding; + use hex_literal::hex; + + #[test] + fn new_success() { + let point = ProjectivePoint::from_bytes( + &hex!("02c9afa9d845ba75166b5c215767b1d6934e50c3db36e89b127b8a622b120f6721").into(), + ) + .unwrap(); + + assert!(bool::from(NonIdentity::new(point).is_some())); + + assert!(bool::from( + NonIdentity::new(AffinePoint::from(point)).is_some() + )); + } + + #[test] + fn new_fail() { + assert!(bool::from( + NonIdentity::new(ProjectivePoint::default()).is_none() + )); + assert!(bool::from( + NonIdentity::new(AffinePoint::default()).is_none() + )); + } + + #[test] + fn round_trip() { + let bytes = hex!("02c9afa9d845ba75166b5c215767b1d6934e50c3db36e89b127b8a622b120f6721"); + let point = NonIdentity::<ProjectivePoint>::from_repr(&bytes.into()).unwrap(); + assert_eq!(&bytes, point.to_bytes().as_slice()); + + let bytes = hex!("02c9afa9d845ba75166b5c215767b1d6934e50c3db36e89b127b8a622b120f6721"); + let point = NonIdentity::<AffinePoint>::from_repr(&bytes.into()).unwrap(); + assert_eq!(&bytes, point.to_bytes().as_slice()); + } +} |