Trait MultiscalarMul

pub trait MultiscalarMul {
    type Point;

    // Required method
    fn multiscalar_mul<I, J>(scalars: I, points: J) -> Self::Point
       where I: IntoIterator,
             I::Item: Borrow<Scalar>,
             J: IntoIterator,
             J::Item: Borrow<Self::Point>;
}

A trait for constant-time multiscalar multiplication without precomputation.

Required Associated Types

type Point

The type of point being multiplied, e.g., RistrettoPoint.

Required Methods

fn multiscalar_mul<I, J>(scalars: I, points: J) -> Self::Point

where I: IntoIterator, I::Item: Borrow<Scalar>, J: IntoIterator, J::Item: Borrow<Self::Point>,

Given an iterator of (possibly secret) scalars and an iterator of public points, compute $$ Q = c_1 P_1 + \cdots + c_n P_n. $$

It is an error to call this function with two iterators of different lengths.

Examples

The trait bound aims for maximum flexibility: the inputs must be convertable to iterators (I: IntoIter), and the iterator’s items must be Borrow<Scalar> (or Borrow<Point>), to allow iterators returning either Scalars or &Scalars.

use curve25519_dalek::constants;
use curve25519_dalek::traits::MultiscalarMul;
use curve25519_dalek::ristretto::RistrettoPoint;
use curve25519_dalek::scalar::Scalar;

// Some scalars
let a = Scalar::from(87329482u64);
let b = Scalar::from(37264829u64);
let c = Scalar::from(98098098u64);

// Some points
let P = constants::RISTRETTO_BASEPOINT_POINT;
let Q = P + P;
let R = P + Q;

// A1 = a*P + b*Q + c*R
let abc = [a,b,c];
let A1 = RistrettoPoint::multiscalar_mul(&abc, &[P,Q,R]);
// Note: (&abc).into_iter(): Iterator<Item=&Scalar>

// A2 = (-a)*P + (-b)*Q + (-c)*R
let minus_abc = abc.iter().map(|x| -x);
let A2 = RistrettoPoint::multiscalar_mul(minus_abc, &[P,Q,R]);
// Note: minus_abc.into_iter(): Iterator<Item=Scalar>

assert_eq!(A1.compress(), (-A2).compress());

Dyn Compatibility

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.

Implementors

impl MultiscalarMul for curve25519_dalek::backend::serial::scalar_mul::straus::Straus

Available on crate feature alloc only.

type Point = EdwardsPoint

impl MultiscalarMul for curve25519_dalek::backend::vector::scalar_mul::straus::spec_avx2::Straus

Available on crate feature alloc and curve25519_dalek_backend="simd" only.

type Point = EdwardsPoint

impl MultiscalarMul for curve25519_dalek::backend::vector::scalar_mul::straus::spec_avx512ifma_avx512vl::Straus

Available on nightly and crate feature alloc and curve25519_dalek_backend="simd" only.

type Point = EdwardsPoint

impl MultiscalarMul for EdwardsPoint

Available on crate feature alloc only.

type Point = EdwardsPoint

impl MultiscalarMul for RistrettoPoint

Available on crate feature alloc only.

type Point = RistrettoPoint