saymrwulf/curve25519-dalek-source
1
0
Fork 0
mirror of https://github.com/saymrwulf/curve25519-dalek-source.git synced 2026-09-04 20:24:10 +00:00
Code Issues Projects Releases Packages Wiki Activity Actions

Merge remote-tracking branch 'briansmith/addition-chain' into develop

Browse source
This commit is contained in:
Henry de Valence 2017-09-15 16:16:11 -07:00
commit e27bcd0057
1 changed files with 53 additions and 6 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

59
src/scalar.rs
View file

@ -2,11 +2,13 @@
//
// This file is part of curve25519-dalek.
// Copyright (c) 2016-2017 Isis Lovecruft, Henry de Valence
// Portions Copyright 2017 Brian Smith
// See LICENSE for licensing information.
//
// Authors:
// - Isis Agora Lovecruft <isis@patternsinthevoid.net>
// - Henry de Valence <hdevalence@hdevalence.ca>
// - Brian Smith <brian@briansmith.org>
//! Arithmetic for scalar multiplication.
//!
@ -565,14 +567,59 @@ impl UnpackedScalar {
/// Compute the multiplicative inverse of this scalar.
pub fn invert(&self) -> UnpackedScalar {
let mut y = UnpackedScalar::one();
// Run through bits of l-2 from highest to least
for bit in constants::l_minus_2.bits().iter().rev() {
y = y.square();
if *bit == 1 {
y = UnpackedScalar::multiply_add(&y, self, &UnpackedScalar::zero());
// This is a direct transliteration of the addition chain from
// https://briansmith.org/ecc-inversion-addition-chains-01#curve25519_scalar_inversion
// as it was published on 2017-09-03.
let _1 = *self;
let _10 = _1.square();
let _100 = _10.square();
let _11 = UnpackedScalar::multiply_add(&_10, &_1, &UnpackedScalar::zero());
let _101 = UnpackedScalar::multiply_add(&_10, &_11, &UnpackedScalar::zero());
let _111 = UnpackedScalar::multiply_add(&_10, &_101, &UnpackedScalar::zero());
let _1001 = UnpackedScalar::multiply_add(&_10, &_111, &UnpackedScalar::zero());
let _1011 = UnpackedScalar::multiply_add(&_10, &_1001, &UnpackedScalar::zero());
let _1111 = UnpackedScalar::multiply_add(&_100, &_1011, &UnpackedScalar::zero());
// _10000
let mut y = UnpackedScalar::multiply_add(&_1111, &_1, &UnpackedScalar::zero());
#[inline]
fn square_multiply(y: &mut UnpackedScalar, squarings: usize, x: &UnpackedScalar) {
for _ in 0..squarings {
*y = y.square();
}
*y = UnpackedScalar::multiply_add(y, x, &UnpackedScalar::zero());
}
square_multiply(&mut y, 123 + 3, &_101);
square_multiply(&mut y, 2 + 2, &_11);
square_multiply(&mut y, 1 + 4, &_1111);
square_multiply(&mut y, 1 + 4, &_1111);
square_multiply(&mut y, 4, &_1001);
square_multiply(&mut y, 2, &_11);
square_multiply(&mut y, 1 + 4, &_1111);
square_multiply(&mut y, 1 + 3, &_101);
square_multiply(&mut y, 3 + 3, &_101);
square_multiply(&mut y, 3, &_111);
square_multiply(&mut y, 1 + 4, &_1111);
square_multiply(&mut y, 2 + 3, &_111);
square_multiply(&mut y, 2 + 2, &_11);
square_multiply(&mut y, 1 + 4, &_1011);
square_multiply(&mut y, 2 + 4, &_1011);
square_multiply(&mut y, 6 + 4, &_1001);
square_multiply(&mut y, 2 + 2, &_11);
square_multiply(&mut y, 3 + 2, &_11);
square_multiply(&mut y, 3 + 2, &_11);
square_multiply(&mut y, 1 + 4, &_1001);
square_multiply(&mut y, 1 + 3, &_111);
square_multiply(&mut y, 2 + 4, &_1111);
square_multiply(&mut y, 1 + 4, &_1011);
square_multiply(&mut y, 3, &_101);
square_multiply(&mut y, 2 + 4, &_1111);
square_multiply(&mut y, 3, &_101);
square_multiply(&mut y, 1 + 2, &_11);
y
}