testudo/src/group.rs

use super::scalar::{Scalar, ScalarBytes, ScalarBytesFromScalar};
use core::borrow::Borrow;
use core::ops::{Mul, MulAssign};

pub type GroupElement = curve25519_dalek::ristretto::RistrettoPoint;
pub type CompressedGroup = curve25519_dalek::ristretto::CompressedRistretto;
pub const GROUP_BASEPOINT_COMPRESSED: CompressedGroup =
  curve25519_dalek::constants::RISTRETTO_BASEPOINT_COMPRESSED;

impl<'b> MulAssign<&'b Scalar> for GroupElement {
  fn mul_assign(&mut self, scalar: &'b Scalar) {
    let result = (self as &GroupElement) * Scalar::decompress_scalar(scalar);
    *self = result;
  }
}

impl<'a, 'b> Mul<&'b Scalar> for &'a GroupElement {
  type Output = GroupElement;
  fn mul(self, scalar: &'b Scalar) -> GroupElement {
    self * Scalar::decompress_scalar(scalar)
  }
}

impl<'a, 'b> Mul<&'b GroupElement> for &'a Scalar {
  type Output = GroupElement;

  fn mul(self, point: &'b GroupElement) -> GroupElement {
    Scalar::decompress_scalar(self) * point
  }
}

macro_rules! define_mul_variants {
  (LHS = $lhs:ty, RHS = $rhs:ty, Output = $out:ty) => {
    impl<'b> Mul<&'b $rhs> for $lhs {
      type Output = $out;
      fn mul(self, rhs: &'b $rhs) -> $out {
        &self * rhs
      }
    }

    impl<'a> Mul<$rhs> for &'a $lhs {
      type Output = $out;
      fn mul(self, rhs: $rhs) -> $out {
        self * &rhs
      }
    }

    impl Mul<$rhs> for $lhs {
      type Output = $out;
      fn mul(self, rhs: $rhs) -> $out {
        &self * &rhs
      }
    }
  };
}

macro_rules! define_mul_assign_variants {
  (LHS = $lhs:ty, RHS = $rhs:ty) => {
    impl MulAssign<$rhs> for $lhs {
      fn mul_assign(&mut self, rhs: $rhs) {
        *self *= &rhs;
      }
    }
  };
}

define_mul_assign_variants!(LHS = GroupElement, RHS = Scalar);
define_mul_variants!(LHS = GroupElement, RHS = Scalar, Output = GroupElement);
define_mul_variants!(LHS = Scalar, RHS = GroupElement, Output = GroupElement);

pub trait VartimeMultiscalarMul {
  type Scalar;
  fn vartime_multiscalar_mul<I, J>(scalars: I, points: J) -> Self
  where
    I: IntoIterator,
    I::Item: Borrow<Self::Scalar>,
    J: IntoIterator,
    J::Item: Borrow<Self>,
    Self: Clone;
}

impl VartimeMultiscalarMul for GroupElement {
  type Scalar = super::scalar::Scalar;
  fn vartime_multiscalar_mul<I, J>(scalars: I, points: J) -> Self
  where
    I: IntoIterator,
    I::Item: Borrow<Self::Scalar>,
    J: IntoIterator,
    J::Item: Borrow<Self>,
    Self: Clone,
  {
    use curve25519_dalek::traits::VartimeMultiscalarMul;
    <Self as VartimeMultiscalarMul>::vartime_multiscalar_mul(
      scalars
        .into_iter()
        .map(|s| Scalar::decompress_scalar(s.borrow()))
        .collect::<Vec<ScalarBytes>>(),
      points,
    )
  }
}