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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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36
crypto/ed448/src/backend.rs
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@@ -94,8 +94,8 @@ macro_rules! field {
use $crate::backend::u8_from_bool;
fn reduce(x: U1024) -> U512 {
U512::from_le_slice(&x.rem(&NonZero::new($WIDE_MODULUS).unwrap()).to_le_bytes()[.. 64])
fn reduce(x: U896) -> U448 {
U448::from_le_slice(&x.rem(&NonZero::new($WIDE_MODULUS).unwrap()).to_le_bytes()[.. 56])
}
impl ConstantTimeEq for $FieldName {
@@ -117,11 +117,11 @@ macro_rules! field {
math_op!($FieldName, $FieldName, Mul, mul, MulAssign, mul_assign, |x: $ResidueType, y| x
.mul(&y));
from_wrapper!($FieldName, U512, u8);
from_wrapper!($FieldName, U512, u16);
from_wrapper!($FieldName, U512, u32);
from_wrapper!($FieldName, U512, u64);
from_wrapper!($FieldName, U512, u128);
from_wrapper!($FieldName, U448, u8);
from_wrapper!($FieldName, U448, u16);
from_wrapper!($FieldName, U448, u32);
from_wrapper!($FieldName, U448, u64);
from_wrapper!($FieldName, U448, u128);
impl Neg for $FieldName {
type Output = $FieldName;
@@ -173,9 +173,9 @@ macro_rules! field {
const ONE: Self = Self(Residue::ONE);
fn random(mut rng: impl RngCore) -> Self {
let mut bytes = [0; 128];
let mut bytes = [0; 112];
rng.fill_bytes(&mut bytes);
$FieldName(Residue::new(&reduce(U1024::from_le_slice(bytes.as_ref()))))
$FieldName(Residue::new(&reduce(U896::from_le_slice(bytes.as_ref()))))
}
fn square(&self) -> Self {
@@ -187,13 +187,13 @@ macro_rules! field {
fn invert(&self) -> CtOption<Self> {
const NEG_2: $FieldName =
Self($ResidueType::sub(&$ResidueType::ZERO, &$ResidueType::new(&U512::from_u8(2))));
Self($ResidueType::sub(&$ResidueType::ZERO, &$ResidueType::new(&U448::from_u8(2))));
CtOption::new(self.pow(NEG_2), !self.is_zero())
}
fn sqrt(&self) -> CtOption<Self> {
const MOD_1_4: $FieldName = Self($ResidueType::new(
&$MODULUS.saturating_add(&U512::ONE).wrapping_div(&U512::from_u8(4)),
&$MODULUS.saturating_add(&U448::ONE).wrapping_div(&U448::from_u8(4)),
));
let res = self.pow(MOD_1_4);
@@ -213,27 +213,27 @@ macro_rules! field {
const NUM_BITS: u32 = $NUM_BITS;
const CAPACITY: u32 = $NUM_BITS - 1;
const TWO_INV: Self = $FieldName($ResidueType::new(&U512::from_u8(2)).invert().0);
const TWO_INV: Self = $FieldName($ResidueType::new(&U448::from_u8(2)).invert().0);
const MULTIPLICATIVE_GENERATOR: Self =
Self(Residue::new(&U512::from_u8($MULTIPLICATIVE_GENERATOR)));
Self(Residue::new(&U448::from_u8($MULTIPLICATIVE_GENERATOR)));
// True for both the Ed448 Scalar field and FieldElement field
const S: u32 = 1;
// Both fields have their root of unity as -1
const ROOT_OF_UNITY: Self =
Self($ResidueType::sub(&$ResidueType::ZERO, &$ResidueType::new(&U512::ONE)));
Self($ResidueType::sub(&$ResidueType::ZERO, &$ResidueType::new(&U448::ONE)));
const ROOT_OF_UNITY_INV: Self = Self(Self::ROOT_OF_UNITY.0.invert().0);
const DELTA: Self = $FieldName(Residue::new(&U512::from_le_hex($DELTA)));
const DELTA: Self = $FieldName(Residue::new(&U448::from_le_hex($DELTA)));
fn from_repr(bytes: Self::Repr) -> CtOption<Self> {
let res = U512::from_le_slice(&[bytes.as_ref(), [0; 7].as_ref()].concat());
CtOption::new($FieldName(Residue::new(&res)), res.ct_lt(&$MODULUS))
let res = U448::from_le_slice(&bytes[.. 56]);
CtOption::new($FieldName(Residue::new(&res)), res.ct_lt(&$MODULUS) & bytes[56].ct_eq(&0))
}
fn to_repr(&self) -> Self::Repr {
let mut repr = GenericArray::<u8, U57>::default();
repr.copy_from_slice(&self.0.retrieve().to_le_bytes()[.. 57]);
repr[.. 56].copy_from_slice(&self.0.retrieve().to_le_bytes());
repr
}