pub use super::scalar::{MaskedScalar, Scalar, SCALAR_LEN};
use crate::{
bssl, error,
limb::{Limb, LIMB_BITS},
};
use core::marker::PhantomData;
#[repr(C)]
pub struct Elem<E: Encoding> {
limbs: [Limb; ELEM_LIMBS], encoding: PhantomData<E>,
}
pub trait Encoding {}
pub struct T;
impl Encoding for T {}
const ELEM_LIMBS: usize = 5 * 64 / LIMB_BITS;
impl<E: Encoding> Elem<E> {
fn zero() -> Self {
Self {
limbs: Default::default(),
encoding: PhantomData,
}
}
}
impl Elem<T> {
fn negate(&mut self) {
unsafe {
x25519_fe_neg(self);
}
}
}
pub type EncodedPoint = [u8; ELEM_LEN];
pub const ELEM_LEN: usize = 32;
#[repr(C)]
pub struct ExtPoint {
x: Elem<T>,
y: Elem<T>,
z: Elem<T>,
t: Elem<T>,
}
impl ExtPoint {
pub fn new_at_infinity() -> Self {
Self {
x: Elem::zero(),
y: Elem::zero(),
z: Elem::zero(),
t: Elem::zero(),
}
}
pub fn from_encoded_point_vartime(encoded: &EncodedPoint) -> Result<Self, error::Unspecified> {
let mut point = Self::new_at_infinity();
Result::from(unsafe { x25519_ge_frombytes_vartime(&mut point, encoded) }).map(|()| point)
}
pub fn into_encoded_point(self) -> EncodedPoint {
encode_point(self.x, self.y, self.z)
}
pub fn invert_vartime(&mut self) {
self.x.negate();
self.t.negate();
}
}
#[repr(C)]
pub struct Point {
x: Elem<T>,
y: Elem<T>,
z: Elem<T>,
}
impl Point {
pub fn new_at_infinity() -> Self {
Self {
x: Elem::zero(),
y: Elem::zero(),
z: Elem::zero(),
}
}
pub fn into_encoded_point(self) -> EncodedPoint {
encode_point(self.x, self.y, self.z)
}
}
fn encode_point(x: Elem<T>, y: Elem<T>, z: Elem<T>) -> EncodedPoint {
let mut bytes = [0; ELEM_LEN];
let sign_bit: u8 = unsafe {
let mut recip = Elem::zero();
x25519_fe_invert(&mut recip, &z);
let mut x_over_z = Elem::zero();
x25519_fe_mul_ttt(&mut x_over_z, &x, &recip);
let mut y_over_z = Elem::zero();
x25519_fe_mul_ttt(&mut y_over_z, &y, &recip);
x25519_fe_tobytes(&mut bytes, &y_over_z);
x25519_fe_isnegative(&x_over_z)
};
bytes[ELEM_LEN - 1] ^= sign_bit << 7;
bytes
}
prefixed_extern! {
fn x25519_fe_invert(out: &mut Elem<T>, z: &Elem<T>);
fn x25519_fe_isnegative(elem: &Elem<T>) -> u8;
fn x25519_fe_mul_ttt(h: &mut Elem<T>, f: &Elem<T>, g: &Elem<T>);
fn x25519_fe_neg(f: &mut Elem<T>);
fn x25519_fe_tobytes(bytes: &mut EncodedPoint, elem: &Elem<T>);
fn x25519_ge_frombytes_vartime(h: &mut ExtPoint, s: &EncodedPoint) -> bssl::Result;
}