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Ensure that all Scalars are bounded by 2^255.

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This commit defines a Scalar to hold an integer representing an element of
Z/lZ.  Applications like X/Ed25519 that care about the bit-patterns of the
scalars they use can set a specific bit-pattern using the `from_bits`
constructor.  Applications that want to treat scalars as integers mod l can use
the `from_bytes_mod_order` constructor.  Either way, the constructor ensures
that the integer representing each Scalar is bounded by 2^255 so that the high
bit is set.  This means that any Scalar object is always safe to use for scalar
multiplication, while maintaining compatibility with both the Ristretto
use-case and the X/Ed25519 usecase.
This commit is contained in:
Henry de Valence 2017-11-22 16:04:47 -08:00
parent d88f92276a
commit d32fe9772b
4 changed files with 206 additions and 132 deletions
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34
src/constants.rs
View file

@ -64,28 +64,34 @@ pub const RISTRETTO_BASEPOINT_POINT: RistrettoPoint = RistrettoPoint(ED25519_BAS
/// `BASEPOINT_ORDER` is the order of base point, i.e. `l = 2^252 +
/// 27742317777372353535851937790883648493`, in little-endian bytes.
pub const BASEPOINT_ORDER: Scalar = Scalar([
0xed, 0xd3, 0xf5, 0x5c, 0x1a, 0x63, 0x12, 0x58,
0xd6, 0x9c, 0xf7, 0xa2, 0xde, 0xf9, 0xde, 0x14,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x10,
]);
pub const BASEPOINT_ORDER: Scalar = Scalar{
bytes: [
0xed, 0xd3, 0xf5, 0x5c, 0x1a, 0x63, 0x12, 0x58,
0xd6, 0x9c, 0xf7, 0xa2, 0xde, 0xf9, 0xde, 0x14,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x10,
],
};
/// `BASEPOINT_ORDER_MINUS_1` is the order of base point minus one, i.e. `l-1`, in little-endian bytes.
pub const BASEPOINT_ORDER_MINUS_1: Scalar = Scalar([
0xec, 0xd3, 0xf5, 0x5c, 0x1a, 0x63, 0x12, 0x58,
0xd6, 0x9c, 0xf7, 0xa2, 0xde, 0xf9, 0xde, 0x14,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x10,
]);
pub const BASEPOINT_ORDER_MINUS_1: Scalar = Scalar{
bytes: [
0xec, 0xd3, 0xf5, 0x5c, 0x1a, 0x63, 0x12, 0x58,
0xd6, 0x9c, 0xf7, 0xa2, 0xde, 0xf9, 0xde, 0x14,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x10,
],
};
/// `BASEPOINT_ORDER_MINUS_2` is the order of base point minus two, i.e. `l-2`, in little-endian bytes.
pub const BASEPOINT_ORDER_MINUS_2: Scalar = Scalar([
pub const BASEPOINT_ORDER_MINUS_2: Scalar = Scalar{
bytes: [
0xeb, 0xd3, 0xf5, 0x5c, 0x1a, 0x63, 0x12, 0x58,
0xd6, 0x9c, 0xf7, 0xa2, 0xde, 0xf9, 0xde, 0x14,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x10,
]);
],
};
// Precomputed basepoint table is generated into a file by build.rs

30
src/edwards.rs
View file

@ -878,18 +878,24 @@ mod test {
0x72, 0xc3, 0x7f, 0x82, 0xf2, 0x96, 0x96, 0x70]);
/// 4493907448824000747700850167940867464579944529806937181821189941592931634714
pub static A_SCALAR: Scalar = Scalar([
0x1a, 0x0e, 0x97, 0x8a, 0x90, 0xf6, 0x62, 0x2d,
0x37, 0x47, 0x02, 0x3f, 0x8a, 0xd8, 0x26, 0x4d,
0xa7, 0x58, 0xaa, 0x1b, 0x88, 0xe0, 0x40, 0xd1,
0x58, 0x9e, 0x7b, 0x7f, 0x23, 0x76, 0xef, 0x09]);
pub static A_SCALAR: Scalar = Scalar{
bytes: [
0x1a, 0x0e, 0x97, 0x8a, 0x90, 0xf6, 0x62, 0x2d,
0x37, 0x47, 0x02, 0x3f, 0x8a, 0xd8, 0x26, 0x4d,
0xa7, 0x58, 0xaa, 0x1b, 0x88, 0xe0, 0x40, 0xd1,
0x58, 0x9e, 0x7b, 0x7f, 0x23, 0x76, 0xef, 0x09,
],
};
/// 2506056684125797857694181776241676200180934651973138769173342316833279714961
pub static B_SCALAR: Scalar = Scalar([
0x91, 0x26, 0x7a, 0xcf, 0x25, 0xc2, 0x09, 0x1b,
0xa2, 0x17, 0x74, 0x7b, 0x66, 0xf0, 0xb3, 0x2e,
0x9d, 0xf2, 0xa5, 0x67, 0x41, 0xcf, 0xda, 0xc4,
0x56, 0xa7, 0xd4, 0xaa, 0xb8, 0x60, 0x8a, 0x05]);
pub static B_SCALAR: Scalar = Scalar{
bytes: [
0x91, 0x26, 0x7a, 0xcf, 0x25, 0xc2, 0x09, 0x1b,
0xa2, 0x17, 0x74, 0x7b, 0x66, 0xf0, 0xb3, 0x2e,
0x9d, 0xf2, 0xa5, 0x67, 0x41, 0xcf, 0xda, 0xc4,
0x56, 0xa7, 0xd4, 0xaa, 0xb8, 0x60, 0x8a, 0x05,
],
};
/// A_SCALAR * basepoint, computed with ed25519.py
pub static A_TIMES_BASEPOINT: CompressedEdwardsY = CompressedEdwardsY([
@ -1050,8 +1056,8 @@ mod test {
#[test]
#[cfg(feature="precomputed_tables")]
fn basepoint_mult_two_vs_basepoint2() {
let mut two_bytes = [0u8; 32]; two_bytes[0] = 2;
let bp2 = &constants::ED25519_BASEPOINT_TABLE * &Scalar(two_bytes);
let two = Scalar::from_u64(2);
let bp2 = &constants::ED25519_BASEPOINT_TABLE * &two;
assert_eq!(bp2.compress(), BASE2_CMPRSSD);
}

14
src/montgomery.rs
View file

@ -549,20 +549,6 @@ mod test {
assert_eq!(result.compress(), expected.to_montgomery().compress());
}
#[test]
#[should_panic(expected = "assertion failed: self[31] <= 127")]
#[cfg(feature="precomputed_tables")]
fn ladder_matches_scalarmult_with_scalar_high_bit_set() {
let mut s: Scalar = Scalar::one();
s[31] = 255;
let result: MontgomeryPoint = &BASE_COMPRESSED_MONTGOMERY.decompress() * &s;
let expected: ExtendedPoint = &constants::ED25519_BASEPOINT_TABLE * &s;
assert_eq!(result.compress(), expected.to_montgomery().compress())
}
}
#[cfg(all(test, feature = "bench"))]

260
src/scalar.rs
View file

@ -12,28 +12,31 @@
//! Arithmetic for scalar multiplication.
//!
//! The Ed25519 basepoint P has prime order
//! Both the Ristretto group and the Ed25519 basepoint have prime order
//! \\( \ell = 2\^{252} + 27742317777372353535851937790883648493 \\).
//!
//! l = 2^252 + 27742317777372353535851937790883648493.
//! The `Scalar` struct holds an integer \\(s < 2\^{255} \\) which
//! represents an element of \\(\mathbb Z / \ell\\).
//!
//! Thus a multiple `aP` of the basepoint (with a ∈ ℤ) depends only
//! on the value of `a (mod l)`, or equivalently, the image of `a` in
//! the quotient ℤ/lℤ.
//! The code is intended to be useful with both the Ristretto group
//! (where everything is done modulo \\( \ell \\), and the X/Ed25519
//! setting, which mandates specific bit-twiddles that are not
//! well-defined modulo \\( \ell \\).
//!
//! The `Scalar` struct represents an element in ℤ/lℤ.
//! To create a `Scalar` by reducing a 256-bit integer mod \\( \ell \\),
//! use `Scalar::from_bytes_mod_order`.
//!
//! In contrast to `FieldElement`s, `Scalar`s are stored in
//! memory as bytes, allowing easy access to the bits of the `Scalar`
//! when multiplying a point by a scalar. For efficient arithmetic
//! between two scalars, the `UnpackedScalar` struct (internally
//! either `Scalar32` or `Scalar64`) is stored as limbs.
//! To create a `Scalar` with a specific bit-pattern (e.g., for
//! compatibility with X25519 "clamping"), use `Scalar::from_bits`.
//!
//! All arithmetic on `Scalars` is done modulo \\( \ell \\).
use core::fmt::Debug;
use core::ops::Neg;
use core::ops::{Add, AddAssign};
use core::ops::{Sub, SubAssign};
use core::ops::{Mul, MulAssign};
use core::ops::{Index, IndexMut};
use core::ops::{Index};
use core::cmp::{Eq, PartialEq};
#[cfg(feature = "std")]
@ -50,10 +53,16 @@ use backend;
use constants;
/// An `UnpackedScalar` represents an element of the field GF(l), optimized for speed.
///
/// This is a type alias for one of the scalar types in the `backend`
/// module.
#[cfg(feature="radix_51")]
type UnpackedScalar = backend::u64::scalar::Scalar64;
/// An `UnpackedScalar` represents an element of the field GF(l), optimized for speed.
///
/// This is a type alias for one of the scalar types in the `backend`
/// module.
#[cfg(not(feature="radix_51"))]
type UnpackedScalar = backend::u32::scalar::Scalar32;
@ -64,11 +73,47 @@ type UnpackedScalar = backend::u32::scalar::Scalar32;
///
/// is the order of the basepoint. The `Scalar` is stored as bytes.
#[derive(Copy, Clone)]
pub struct Scalar(pub [u8; 32]);
pub struct Scalar {
/// `bytes` is a little-endian byte encoding of an integer representing a scalar modulo the group order.
///
/// # Invariant
///
/// The integer representing this scalar must be bounded above by 2^255, or equivalently the high bit of `bytes[31]` must be zero.
///
// XXX This is pub(crate) so we can write literal constants. If const fns were stable, we could make the Scalar constructors const fns and use those instead.
pub(crate) bytes: [u8; 32],
}
impl Scalar {
/// Construct a `Scalar` by reducing a 256-bit integer modulo the group order.
pub fn from_bytes_mod_order(bytes: [u8;32]) -> Scalar {
// Temporarily allow s_unreduced.bytes > 2^255 ...
let s_unreduced = Scalar{bytes: bytes};
// Then reduce mod the group order and return the reduced representative.
let s = s_unreduced.reduce();
debug_assert_eq!(0u8, s[31] >> 7);
s
}
/// Construct a `Scalar` from the low 255 bits of a 256-bit integer.
///
/// This function is intended for applications like X25519 which
/// require specific bit-patterns when performing scalar
/// multiplication.
pub fn from_bits(bytes: [u8; 32]) -> Scalar {
let mut s = Scalar{bytes: bytes};
// Ensure that s < 2^255 by masking the high bit
s.bytes[31] &= 0b0111_1111;
s
}
}
impl Debug for Scalar {
fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
write!(f, "Scalar: {:?}", &self.0[..])
write!(f, "Scalar{{\n\tbytes: {:?},\n}}", &self.bytes)
}
}
@ -85,7 +130,7 @@ impl PartialEq for Scalar {
///
/// True if they are equal, and false otherwise.
fn eq(&self, other: &Self) -> bool {
slices_equal(&self.0, &other.0) == 1u8
slices_equal(&self.bytes, &other.bytes) == 1u8
}
}
@ -96,21 +141,16 @@ impl Equal for Scalar {
///
/// `1u8` if they are equal, and `0u8` otherwise.
fn ct_eq(&self, other: &Self) -> u8 {
slices_equal(&self.0, &other.0)
slices_equal(&self.bytes, &other.bytes)
}
}
impl Index<usize> for Scalar {
type Output = u8;
/// Index the bytes of the representative for this `Scalar`. Mutation is not permitted.
fn index(&self, _index: usize) -> &u8 {
&(self.0[_index])
}
}
impl IndexMut<usize> for Scalar {
fn index_mut(&mut self, _index: usize) -> &mut u8 {
&mut (self.0[_index])
&(self.bytes[_index])
}
}
@ -169,10 +209,8 @@ impl ConditionallyAssignable for Scalar {
/// # use curve25519_dalek::scalar::Scalar;
/// # use subtle::ConditionallyAssignable;
/// # fn main() {
/// let a = Scalar([0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
/// 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]);
/// let b = Scalar([1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
/// 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1]);
/// let a = Scalar::from_bits([0u8;32]);
/// let b = Scalar::from_bits([1u8;32]);
/// let mut t = a;
/// t.conditional_assign(&b, 0u8);
/// assert!(t[0] == a[0]);
@ -190,7 +228,7 @@ impl ConditionallyAssignable for Scalar {
// if choice = 1u8, mask = (-1i8) as u8 = 11111111
let mask = -(choice as i8) as u8;
for i in 0..32 {
self[i] ^= mask & (self[i] ^ other[i]);
self.bytes[i] ^= mask & (self.bytes[i] ^ other.bytes[i]);
}
}
}
@ -305,27 +343,31 @@ impl Scalar {
/// View this `Scalar` as a sequence of bytes.
pub fn as_bytes(&self) -> &[u8; 32] {
&self.0
&self.bytes
}
/// Construct the additive identity
pub fn zero() -> Self {
Scalar([0u8; 32])
Scalar { bytes: [0u8; 32]}
}
/// Construct the multiplicative identity
pub fn one() -> Self {
Scalar([ 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 ])
Scalar {
bytes: [
1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
],
}
}
/// Construct a scalar from the given `u64`.
pub fn from_u64(x: u64) -> Scalar {
let mut s = Scalar::zero();
let mut s_bytes = [0u8; 32];
for i in 0..8 {
s[i] = (x >> (i*8)) as u8;
s_bytes[i] = (x >> (i*8)) as u8;
}
s
Scalar{ bytes: s_bytes }
}
/// Compute the multiplicative inverse of this scalar.
@ -339,7 +381,7 @@ impl Scalar {
for i in 0..256 {
// As i runs from 0..256, the bottom 3 bits index the bit,
// while the upper bits index the byte.
bits[i] = ((self.0[i>>3] >> (i&7)) & 1u8) as i8;
bits[i] = ((self.bytes[i>>3] >> (i&7)) & 1u8) as i8;
}
bits
}
@ -431,7 +473,7 @@ impl Scalar {
/// Unpack this `Scalar` to an `UnpackedScalar`
pub(crate) fn unpack(&self) -> UnpackedScalar {
UnpackedScalar::from_bytes(&self.0)
UnpackedScalar::from_bytes(&self.bytes)
}
/// Compute `(a * b) + c` (mod l).
@ -456,7 +498,7 @@ impl Scalar {
impl UnpackedScalar {
/// Pack the limbs of this `UnpackedScalar` into a `Scalar`.
fn pack(&self) -> Scalar {
Scalar(self.to_bytes())
Scalar{ bytes: self.to_bytes() }
}
/// Compute the multiplicative inverse of this scalar.
@ -524,48 +566,69 @@ mod test {
use constants;
/// x = 2238329342913194256032495932344128051776374960164957527413114840482143558222
pub static X: Scalar = Scalar(
[0x4e, 0x5a, 0xb4, 0x34, 0x5d, 0x47, 0x08, 0x84,
0x59, 0x13, 0xb4, 0x64, 0x1b, 0xc2, 0x7d, 0x52,
0x52, 0xa5, 0x85, 0x10, 0x1b, 0xcc, 0x42, 0x44,
0xd4, 0x49, 0xf4, 0xa8, 0x79, 0xd9, 0xf2, 0x04]);
pub static X: Scalar = Scalar{
bytes: [
0x4e, 0x5a, 0xb4, 0x34, 0x5d, 0x47, 0x08, 0x84,
0x59, 0x13, 0xb4, 0x64, 0x1b, 0xc2, 0x7d, 0x52,
0x52, 0xa5, 0x85, 0x10, 0x1b, 0xcc, 0x42, 0x44,
0xd4, 0x49, 0xf4, 0xa8, 0x79, 0xd9, 0xf2, 0x04,
],
};
/// 1/x = 6859937278830797291664592131120606308688036382723378951768035303146619657244
pub static XINV: Scalar = Scalar(
[0x1c, 0xdc, 0x17, 0xfc, 0xe0, 0xe9, 0xa5, 0xbb,
0xd9, 0x24, 0x7e, 0x56, 0xbb, 0x01, 0x63, 0x47,
0xbb, 0xba, 0x31, 0xed, 0xd5, 0xa9, 0xbb, 0x96,
0xd5, 0x0b, 0xcd, 0x7a, 0x3f, 0x96, 0x2a, 0x0f]);
pub static XINV: Scalar = Scalar{
bytes: [
0x1c, 0xdc, 0x17, 0xfc, 0xe0, 0xe9, 0xa5, 0xbb,
0xd9, 0x24, 0x7e, 0x56, 0xbb, 0x01, 0x63, 0x47,
0xbb, 0xba, 0x31, 0xed, 0xd5, 0xa9, 0xbb, 0x96,
0xd5, 0x0b, 0xcd, 0x7a, 0x3f, 0x96, 0x2a, 0x0f,
],
};
/// y = 2592331292931086675770238855846338635550719849568364935475441891787804997264
pub static Y: Scalar = Scalar(
[0x90, 0x76, 0x33, 0xfe, 0x1c, 0x4b, 0x66, 0xa4,
0xa2, 0x8d, 0x2d, 0xd7, 0x67, 0x83, 0x86, 0xc3,
0x53, 0xd0, 0xde, 0x54, 0x55, 0xd4, 0xfc, 0x9d,
0xe8, 0xef, 0x7a, 0xc3, 0x1f, 0x35, 0xbb, 0x05]);
pub static Y: Scalar = Scalar{
bytes: [
0x90, 0x76, 0x33, 0xfe, 0x1c, 0x4b, 0x66, 0xa4,
0xa2, 0x8d, 0x2d, 0xd7, 0x67, 0x83, 0x86, 0xc3,
0x53, 0xd0, 0xde, 0x54, 0x55, 0xd4, 0xfc, 0x9d,
0xe8, 0xef, 0x7a, 0xc3, 0x1f, 0x35, 0xbb, 0x05,
],
};
/// z = 5033871415930814945849241457262266927579821285980625165479289807629491019013
pub static Z: Scalar = Scalar(
[0x05, 0x9d, 0x3e, 0x0b, 0x09, 0x26, 0x50, 0x3d,
0xa3, 0x84, 0xa1, 0x3c, 0x92, 0x7a, 0xc2, 0x06,
0x41, 0x98, 0xcf, 0x34, 0x3a, 0x24, 0xd5, 0xb7,
0xeb, 0x33, 0x6a, 0x2d, 0xfc, 0x11, 0x21, 0x0b]);
pub static Z: Scalar = Scalar{
bytes: [
0x05, 0x9d, 0x3e, 0x0b, 0x09, 0x26, 0x50, 0x3d,
0xa3, 0x84, 0xa1, 0x3c, 0x92, 0x7a, 0xc2, 0x06,
0x41, 0x98, 0xcf, 0x34, 0x3a, 0x24, 0xd5, 0xb7,
0xeb, 0x33, 0x6a, 0x2d, 0xfc, 0x11, 0x21, 0x0b,
],
};
/// w = 3486911242272497535104403593250518247409663771668155364040899665266216860804
static W: Scalar = Scalar(
[0x84, 0xfc, 0xbc, 0x4f, 0x78, 0x12, 0xa0, 0x06,
0xd7, 0x91, 0xd9, 0x7a, 0x3a, 0x27, 0xdd, 0x1e,
0x21, 0x43, 0x45, 0xf7, 0xb1, 0xb9, 0x56, 0x7a,
0x81, 0x30, 0x73, 0x44, 0x96, 0x85, 0xb5, 0x07]);
static W: Scalar = Scalar{
bytes: [
0x84, 0xfc, 0xbc, 0x4f, 0x78, 0x12, 0xa0, 0x06,
0xd7, 0x91, 0xd9, 0x7a, 0x3a, 0x27, 0xdd, 0x1e,
0x21, 0x43, 0x45, 0xf7, 0xb1, 0xb9, 0x56, 0x7a,
0x81, 0x30, 0x73, 0x44, 0x96, 0x85, 0xb5, 0x07,
],
};
/// x*y = 5690045403673944803228348699031245560686958845067437804563560795922180092780
static X_TIMES_Y: Scalar = Scalar(
[0x6c, 0x33, 0x74, 0xa1, 0x89, 0x4f, 0x62, 0x21,
0x0a, 0xaa, 0x2f, 0xe1, 0x86, 0xa6, 0xf9, 0x2c,
0xe0, 0xaa, 0x75, 0xc2, 0x77, 0x95, 0x81, 0xc2,
0x95, 0xfc, 0x08, 0x17, 0x9a, 0x73, 0x94, 0x0c]);
static X_TIMES_Y: Scalar = Scalar{
bytes: [
0x6c, 0x33, 0x74, 0xa1, 0x89, 0x4f, 0x62, 0x21,
0x0a, 0xaa, 0x2f, 0xe1, 0x86, 0xa6, 0xf9, 0x2c,
0xe0, 0xaa, 0x75, 0xc2, 0x77, 0x95, 0x81, 0xc2,
0x95, 0xfc, 0x08, 0x17, 0x9a, 0x73, 0x94, 0x0c,
],
};
static A_SCALAR: Scalar = Scalar([
0x1a, 0x0e, 0x97, 0x8a, 0x90, 0xf6, 0x62, 0x2d,
0x37, 0x47, 0x02, 0x3f, 0x8a, 0xd8, 0x26, 0x4d,
0xa7, 0x58, 0xaa, 0x1b, 0x88, 0xe0, 0x40, 0xd1,
0x58, 0x9e, 0x7b, 0x7f, 0x23, 0x76, 0xef, 0x09]);
static A_SCALAR: Scalar = Scalar{
bytes: [
0x1a, 0x0e, 0x97, 0x8a, 0x90, 0xf6, 0x62, 0x2d,
0x37, 0x47, 0x02, 0x3f, 0x8a, 0xd8, 0x26, 0x4d,
0xa7, 0x58, 0xaa, 0x1b, 0x88, 0xe0, 0x40, 0xd1,
0x58, 0x9e, 0x7b, 0x7f, 0x23, 0x76, 0xef, 0x09,
],
};
static A_NAF: [i8; 256] =
[0,13,0,0,0,0,0,0,0,7,0,0,0,0,0,0,-9,0,0,0,0,-11,0,0,0,0,3,0,0,0,0,1,
@ -586,9 +649,9 @@ mod test {
// LE bytes of 6432735165214683820902750800207468552549813371247423777071615116673864412038
let c_bytes = [134, 171, 119, 216, 180, 128, 178, 62, 171, 132, 32, 62, 34, 119, 104, 193, 47, 215, 181, 250, 14, 207, 172, 93, 75, 207, 211, 103, 144, 204, 56, 14];
let a = Scalar(a_bytes);
let b = Scalar(b_bytes);
let c = Scalar(c_bytes);
let a = Scalar::from_bytes_mod_order(a_bytes);
let b = Scalar::from_bytes_mod_order(b_bytes);
let c = Scalar::from_bytes_mod_order(c_bytes);
let mut tmp = [0u8; 64];
@ -641,8 +704,7 @@ mod test {
#[test]
fn impl_add() {
let mut two = Scalar::zero(); two[0] = 2;
let two = two;
let two = Scalar::from_u64(2);
let one = Scalar::one();
let should_be_two = &one + &one;
assert_eq!(should_be_two, two);
@ -680,13 +742,19 @@ mod test {
#[test]
fn reduce() {
let biggest = Scalar([0xff; 32]);
let biggest = Scalar::from_bytes_mod_order([0xff; 32]);
// sage: l = 2^252 + 27742317777372353535851937790883648493
// sage: big = 2^256 - 1
// sage: repr((big % l).digits(256))
let biggest_mod_l = Scalar([28, 149, 152, 141, 116, 49, 236, 214, 112, 207, 125, 115, 244, 91, 239, 198, 254, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 15]);
let reduced = biggest.reduce();
assert_eq!(reduced, biggest_mod_l);
let biggest_mod_l = Scalar{
bytes: [
28, 149, 152, 141, 116, 49, 236, 214,
112, 207, 125, 115, 244, 91, 239, 198,
254, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 15,
],
};
assert_eq!(biggest, biggest_mod_l);
}
#[test]
@ -699,10 +767,14 @@ mod test {
}
// 3958878930004874126169954872055634648693766179881526445624823978500314864344
// = x + 2^256x (mod l)
let reduced = 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{
bytes: [
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 test_red = Scalar::reduce_wide(&bignum);
for i in 0..32 {
assert!(test_red[i] == reduced[i]);
@ -748,14 +820,18 @@ mod test {
}
// 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 expected = Scalar{
bytes: [
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_wide(&bignum);
// The reduced scalar should match the expected
assert_eq!(reduced.0, expected.0);
assert_eq!(reduced.bytes, expected.bytes);
// (x + 2^256x) * R
let interim = UnpackedScalar::mul_internal(&UnpackedScalar::from_bytes_wide(&bignum),
@ -790,7 +866,7 @@ mod bench {
#[bench]
fn reduce(b: &mut Bencher) {
let unreduced = Scalar([0xff; 32]);
let unreduced = Scalar::from_bits([0xff; 32]);
b.iter(|| unreduced.reduce());
}