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use crate::{digest, error, limb};
use core::convert::TryInto;
#[repr(transparent)]
pub struct Scalar([u8; SCALAR_LEN]);
pub const SCALAR_LEN: usize = 32;
impl Scalar {
pub fn from_bytes_checked(bytes: [u8; SCALAR_LEN]) -> Result<Self, error::Unspecified> {
const ORDER: [limb::Limb; SCALAR_LEN / limb::LIMB_BYTES] =
limbs![0x5cf5d3ed, 0x5812631a, 0xa2f79cd6, 0x14def9de, 0, 0, 0, 0x10000000];
let mut reversed = bytes;
reversed.reverse();
let mut limbs = [0; SCALAR_LEN / limb::LIMB_BYTES];
limb::parse_big_endian_in_range_and_pad_consttime(
untrusted::Input::from(&reversed),
limb::AllowZero::Yes,
&ORDER,
&mut limbs,
)?;
Ok(Self(bytes))
}
pub fn from_sha512_digest_reduced(digest: digest::Digest) -> Self {
extern "C" {
fn GFp_x25519_sc_reduce(s: &mut UnreducedScalar);
}
let mut unreduced = [0u8; digest::SHA512_OUTPUT_LEN];
unreduced.copy_from_slice(digest.as_ref());
unsafe { GFp_x25519_sc_reduce(&mut unreduced) };
Self((&unreduced[..SCALAR_LEN]).try_into().unwrap())
}
}
#[repr(transparent)]
pub struct MaskedScalar([u8; SCALAR_LEN]);
impl MaskedScalar {
pub fn from_bytes_masked(bytes: [u8; SCALAR_LEN]) -> Self {
extern "C" {
fn GFp_x25519_sc_mask(a: &mut [u8; SCALAR_LEN]);
}
let mut r = Self(bytes);
unsafe { GFp_x25519_sc_mask(&mut r.0) };
r
}
}
impl From<MaskedScalar> for Scalar {
fn from(MaskedScalar(scalar): MaskedScalar) -> Self {
Self(scalar)
}
}
type UnreducedScalar = [u8; UNREDUCED_SCALAR_LEN];
const UNREDUCED_SCALAR_LEN: usize = SCALAR_LEN * 2;