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Use U448 for Ed448 instead of U512

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This commit is contained in:
Luke Parker
2023-05-09 04:12:13 -04:00
parent 219adc7657
commit 029b6c53a1
5 changed files with 52 additions and 75 deletions
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41
crypto/ed448/src/scalar.rs
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@@ -1,18 +1,16 @@
use zeroize::{DefaultIsZeroes, Zeroize};
use crypto_bigint::{
U512, U1024,
U448, U896, U1024,
modular::constant_mod::{ResidueParams, Residue},
};
const MODULUS_PADDED_STR: &str = concat!(
"00000000000000",
"00",
const MODULUS_STR: &str = concat!(
"3fffffffffffffffffffffffffffffffffffffffffffffffffffffff",
"7cca23e9c44edb49aed63690216cc2728dc58f552378c292ab5844f3",
);
impl_modulus!(ScalarModulus, U512, MODULUS_PADDED_STR);
impl_modulus!(ScalarModulus, U448, MODULUS_STR);
type ResidueType = Residue<ScalarModulus, { ScalarModulus::LIMBS }>;
/// Ed448 Scalar field element.
@@ -21,27 +19,23 @@ pub struct Scalar(pub(crate) ResidueType);
impl DefaultIsZeroes for Scalar {}
const MODULUS_STR: &str = concat!(
"3fffffffffffffffffffffffffffffffffffffffffffffffffffffff",
"7cca23e9c44edb49aed63690216cc2728dc58f552378c292ab5844f3",
);
// 2**446 - 13818066809895115352007386748515426880336692474882178609894547503885
pub(crate) const MODULUS: U512 = U512::from_be_hex(concat!(
"00000000000000",
"00",
pub(crate) const MODULUS: U448 = U448::from_be_hex(MODULUS_STR);
const WIDE_MODULUS: U896 = U896::from_be_hex(concat!(
"00000000000000000000000000000000000000000000000000000000",
"00000000000000000000000000000000000000000000000000000000",
"3fffffffffffffffffffffffffffffffffffffffffffffffffffffff",
"7cca23e9c44edb49aed63690216cc2728dc58f552378c292ab5844f3",
));
const WIDE_MODULUS: U1024 = U1024::from_be_hex(concat!(
"0000000000000000000000000000000000000000000000000000000000000000",
"0000000000000000000000000000000000000000000000000000000000000000",
"00000000000000",
"00",
const WIDE_REDUCTION_MODULUS: NonZero<U1024> = NonZero::from_uint(U1024::from_be_hex(concat!(
"00000000000000000000000000000000",
"00000000000000000000000000000000000000000000000000000000",
"00000000000000000000000000000000000000000000000000000000",
"3fffffffffffffffffffffffffffffffffffffffffffffffffffffff",
"7cca23e9c44edb49aed63690216cc2728dc58f552378c292ab5844f3",
));
)));
field!(
Scalar,
@@ -52,15 +46,18 @@ field!(
446,
2,
concat!(
"0400000000000000000000000000000000000000000000000000000000000000",
"0000000000000000000000000000000000000000000000000000000000000000",
"04000000000000000000000000000000000000000000000000000000",
"00000000000000000000000000000000000000000000000000000000",
),
);
impl Scalar {
/// Perform a wide reduction to obtain a non-biased Scalar.
pub fn wide_reduce(bytes: [u8; 114]) -> Scalar {
Scalar(Residue::new(&reduce(U1024::from_le_slice(&[bytes.as_ref(), &[0; 14]].concat()))))
let wide = U1024::from_le_slice(&[bytes.as_ref(), &[0; 14]].concat());
Scalar(Residue::new(&U448::from_le_slice(
&wide.rem(&WIDE_REDUCTION_MODULUS).to_le_bytes()[.. 56],
)))
}
}