opaque-vx/src/map_to_curve.rs

// Copyright (c) Facebook, Inc. and its affiliates.
//
// This source code is licensed under the MIT license found in the
// LICENSE file in the root directory of this source tree.

//! Defines the GroupWithMapToCurve trait to specify how to map a password to a
//! curve point

use crate::group::Group;
use curve25519_dalek::{edwards::EdwardsPoint, ristretto::RistrettoPoint};

use generic_array::GenericArray;
use hkdf::Hkdf;

/// A subtrait of Group specifying how to has a password into a point
pub trait GroupWithMapToCurve: Group {
    /// transforms a password and optional pepper into a curve point
    fn map_to_curve(password: &[u8], pepper: Option<&[u8]>) -> Self;
}

impl GroupWithMapToCurve for RistrettoPoint {
    fn map_to_curve(password: &[u8], pepper: Option<&[u8]>) -> Self {
        let (hashed_input, _) = Hkdf::<sha2::Sha512>::extract(pepper, password);
        <Self as Group>::hash_to_curve(GenericArray::from_slice(&hashed_input))
    }
}

impl GroupWithMapToCurve for EdwardsPoint {
    fn map_to_curve(password: &[u8], pepper: Option<&[u8]>) -> Self {
        let (hashed_input, _) = Hkdf::<sha2::Sha256>::extract(pepper, password);
        <Self as Group>::hash_to_curve(GenericArray::from_slice(&hashed_input))
    }
}