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Add test that scalar Montgomery reduction matches reduction.

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Isis Lovecruft 2017-10-31 01:18:52 +00:00
parent e2cbec81fc
commit 583a45ddc2
Failed to extract signature
3 changed files with 49 additions and 15 deletions
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32
src/scalar.rs
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@ -731,6 +731,38 @@ mod test {
assert_eq!(should_be_unpacked.0, unpacked.0);
}
#[test]
fn montgomery_reduce_matches_reduce() {
let mut bignum = [0u8; 64];
// set bignum = x + 2^256x
for i in 0..32 {
bignum[ i] = X[i];
bignum[32+i] = X[i];
}
// x + 2^256x (mod l)
// = 3958878930004874126169954872055634648693766179881526445624823978500314864344
let expected = Scalar([216, 154, 179, 139, 210, 121, 2, 71,
69, 99, 158, 216, 23, 173, 63, 100,
204, 0, 91, 50, 219, 153, 57, 249,
28, 82, 31, 197, 100, 165, 192, 8]);
let reduced = Scalar::reduce(&bignum);
// The reduced scalar should match the expected
assert_eq!(reduced.0, expected.0);
// (x + 2^256x) * R
let interim = UnpackedScalar::mul_internal(&UnpackedScalar::from_bytes_wide(&bignum),
&constants::R);
// ((x + 2^256x) * R) / R (mod l)
let montgomery_reduced = UnpackedScalar::montgomery_reduce(&interim);
// The Montgomery reduced scalar should match the reduced one, as well as the expected
assert_eq!(montgomery_reduced.0, reduced.unpack().0);
assert_eq!(montgomery_reduced.0, expected.unpack().0)
}
#[cfg(feature = "serde")]
use serde_cbor;

4
src/scalar_32bit.rs
View file

@ -197,7 +197,7 @@ impl Scalar32 {
///
/// This is implemented with a one-level refined Karatsuba decomposition
#[inline(always)]
fn mul_internal(a: &Scalar32, b: &Scalar32) -> [u64; 17] {
pub (crate) fn mul_internal(a: &Scalar32, b: &Scalar32) -> [u64; 17] {
let mut z = [0u64; 17];
z[0] = m(a[0],b[0]); // c00
@ -289,7 +289,7 @@ impl Scalar32 {
/// Compute `limbs/R` (mod l), where R is the Montgomery modulus 2^261
#[inline(always)]
fn montgomery_reduce(limbs: &[u64; 17]) -> Scalar32 {
pub (crate) fn montgomery_reduce(limbs: &[u64; 17]) -> Scalar32 {
#[inline(always)]
fn part1(sum: u64) -> (u64, u32) {

28
src/scalar_64bit.rs
View file

@ -181,18 +181,20 @@ impl Scalar64 {
/// Compute `a * b`
#[inline(always)]
fn mul_internal(a: &Scalar64, b: &Scalar64) -> [u128; 9] {
[
m(a[0],b[0]),
m(a[0],b[1]) + m(a[1],b[0]),
m(a[0],b[2]) + m(a[1],b[1]) + m(a[2],b[0]),
m(a[0],b[3]) + m(a[1],b[2]) + m(a[2],b[1]) + m(a[3],b[0]),
m(a[0],b[4]) + m(a[1],b[3]) + m(a[2],b[2]) + m(a[3],b[1]) + m(a[4],b[0]),
m(a[1],b[4]) + m(a[2],b[3]) + m(a[3],b[2]) + m(a[4],b[1]),
m(a[2],b[4]) + m(a[3],b[3]) + m(a[4],b[2]),
m(a[3],b[4]) + m(a[4],b[3]),
m(a[4],b[4])
]
pub (crate) fn mul_internal(a: &Scalar64, b: &Scalar64) -> [u128; 9] {
let mut z = [0u128; 9];
z[0] = m(a[0],b[0]);
z[1] = m(a[0],b[1]) + m(a[1],b[0]);
z[2] = m(a[0],b[2]) + m(a[1],b[1]) + m(a[2],b[0]);
z[3] = m(a[0],b[3]) + m(a[1],b[2]) + m(a[2],b[1]) + m(a[3],b[0]);
z[4] = m(a[0],b[4]) + m(a[1],b[3]) + m(a[2],b[2]) + m(a[3],b[1]) + m(a[4],b[0]);
z[5] = m(a[1],b[4]) + m(a[2],b[3]) + m(a[3],b[2]) + m(a[4],b[1]);
z[6] = m(a[2],b[4]) + m(a[3],b[3]) + m(a[4],b[2]);
z[7] = m(a[3],b[4]) + m(a[4],b[3]);
z[8] = m(a[4],b[4]);
z
}
/// Compute `a^2`
@ -220,7 +222,7 @@ impl Scalar64 {
/// Compute `limbs/R` (mod l), where R is the Montgomery modulus 2^260
#[inline(always)]
fn montgomery_reduce(limbs: &[u128; 9]) -> Scalar64 {
pub (crate) fn montgomery_reduce(limbs: &[u128; 9]) -> Scalar64 {
#[inline(always)]
fn part1(sum: u128) -> (u128, u64) {