1 files changed, 57 insertions, 0 deletions
diff --git a/vendor/elliptic-curve/src/hash2curve/isogeny.rs b/vendor/elliptic-curve/src/hash2curve/isogeny.rs
new file mode 100644
index 000000000..fc197246a
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+++ b/vendor/elliptic-curve/src/hash2curve/isogeny.rs
@@ -0,0 +1,57 @@
+//! Traits for mapping an isogeny to another curve
+//!
+//! <https://datatracker.ietf.org/doc/draft-irtf-cfrg-hash-to-curve>
+
+use core::ops::{AddAssign, Mul};
+use ff::Field;
+use generic_array::{typenum::Unsigned, ArrayLength, GenericArray};
+
+/// The coefficients for mapping from one isogenous curve to another
+pub struct IsogenyCoefficients<F: Field + AddAssign + Mul<Output = F>> {
+    /// The coefficients for the x numerator
+    pub xnum: &'static [F],
+    /// The coefficients for the x denominator
+    pub xden: &'static [F],
+    /// The coefficients for the y numerator
+    pub ynum: &'static [F],
+    /// The coefficients for the x denominator
+    pub yden: &'static [F],
+}
+
+/// The [`Isogeny`] methods to map to another curve.
+pub trait Isogeny: Field + AddAssign + Mul<Output = Self> {
+    /// The maximum number of coefficients
+    type Degree: ArrayLength<Self>;
+    /// The isogeny coefficients
+    const COEFFICIENTS: IsogenyCoefficients<Self>;
+
+    /// Map from the isogeny points to the main curve
+    fn isogeny(x: Self, y: Self) -> (Self, Self) {
+        let mut xs = GenericArray::<Self, Self::Degree>::default();
+        xs[0] = Self::one();
+        xs[1] = x;
+        xs[2] = x.square();
+        for i in 3..Self::Degree::to_usize() {
+            xs[i] = xs[i - 1] * x;
+        }
+        let x_num = Self::compute_iso(&xs, Self::COEFFICIENTS.xnum);
+        let x_den = Self::compute_iso(&xs, Self::COEFFICIENTS.xden)
+            .invert()
+            .unwrap();
+        let y_num = Self::compute_iso(&xs, Self::COEFFICIENTS.ynum) * y;
+        let y_den = Self::compute_iso(&xs, Self::COEFFICIENTS.yden)
+            .invert()
+            .unwrap();
+
+        (x_num * x_den, y_num * y_den)
+    }
+
+    /// Compute the ISO transform
+    fn compute_iso(xxs: &[Self], k: &[Self]) -> Self {
+        let mut xx = Self::zero();
+        for (xi, ki) in xxs.iter().zip(k.iter()) {
+            xx += *xi * ki;
+        }
+        xx
+    }
+}