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Shorten the addition chain for P-384 inversion mod n.
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@briansmith
briansmith committed May 3, 2017
1 parent df51498 commit ab4c97d
Showing 1 changed file with 33 additions and 42 deletions.
75 changes: 33 additions & 42 deletions src/ec/suite_b/ops/p384.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -244,21 +244,21 @@ fn p384_scalar_inv_to_mont(a: &Scalar<Unencoded>) -> Scalar<R> {

// Indexes into `d`.
const B_1: usize = 0;
const B_10: usize = 1;
const B_11: usize = 2;
const B_101: usize = 3;
const B_111: usize = 4;
const B_1111: usize = 5;
const DIGIT_COUNT: usize = 6;
const B_11: usize = 1;
const B_101: usize = 2;
const B_111: usize = 3;
const B_1001: usize = 4;
const B_1011: usize = 5;
const B_1101: usize = 6;
const B_1111: usize = 7;
const DIGIT_COUNT: usize = 8;

let mut d = [Scalar::zero(); DIGIT_COUNT];

d[B_1] = to_mont(a);
d[B_10] = sqr (&d[B_1]);
d[B_11] = mul (&d[B_10], &d[B_1]);
d[B_101] = sqr_mul(&d[B_10], 0 + 1, &d[B_1]);
d[B_111] = mul (&d[B_101], &d[B_10]);
d[B_1111] = sqr_mul(&d[B_111], 0 + 1, &d[B_1]);
let b_10 = sqr(&d[B_1]);
for i in B_11..DIGIT_COUNT {
d[i] = mul(&d[i - 1], &b_10);
}

let ff = sqr_mul(&d[B_1111], 0 + 4, &d[B_1111]);
let ffff = sqr_mul(&ff, 0 + 8, &ff);
Expand All @@ -279,54 +279,45 @@ fn p384_scalar_inv_to_mont(a: &Scalar<Unencoded>) -> Scalar<R> {
// 0101100000011010000011011011001001001000101100001010011101111010
// 1110110011101100000110010110101011001100110001010010100101110001

static REMAINING_WINDOWS: [(u8, u8); 48] = [
static REMAINING_WINDOWS: [(u8, u8); 39] = [
( 2, B_11 as u8),
(3 + 3, B_111 as u8),
(1 + 2, B_11 as u8),
(3 + 2, B_11 as u8),
(1 + 1, B_1 as u8),
(2 + 2, B_11 as u8),
(1 + 2, B_11 as u8),
(1 + 4, B_1001 as u8),
( 4, B_1011 as u8),
(6 + 4, B_1111 as u8),
( 3, B_101 as u8),
(4 + 2, B_11 as u8),
(1 + 3, B_111 as u8),
(2 + 3, B_101 as u8),
( 1, B_1 as u8),
(1 + 3, B_111 as u8),
(1 + 4, B_1111 as u8),
( 3, B_101 as u8),
(1 + 2, B_11 as u8),
(6 + 2, B_11 as u8),
(1 + 1, B_1 as u8),
(5 + 2, B_11 as u8),
(1 + 2, B_11 as u8),
(1 + 2, B_11 as u8),
(2 + 1, B_1 as u8),
(2 + 1, B_1 as u8),
(2 + 1, B_1 as u8),
(3 + 1, B_1 as u8),
(1 + 2, B_11 as u8),
(4 + 1, B_1 as u8),
(1 + 1, B_1 as u8),
( 4, B_1011 as u8),
( 4, B_1001 as u8),
(1 + 4, B_1101 as u8),
( 4, B_1101 as u8),
( 4, B_1111 as u8),
(1 + 4, B_1011 as u8),
(6 + 4, B_1101 as u8),
(5 + 4, B_1101 as u8),
( 4, B_1011 as u8),
(2 + 4, B_1001 as u8),
(2 + 1, B_1 as u8),
(3 + 4, B_1011 as u8),
(4 + 3, B_101 as u8),
(2 + 3, B_111 as u8),
(1 + 4, B_1111 as u8),
(1 + 1, B_1 as u8),
(1 + 3, B_111 as u8),
(1 + 2, B_11 as u8),
(1 + 4, B_1011 as u8),
( 4, B_1011 as u8),
(2 + 3, B_111 as u8),
(1 + 2, B_11 as u8),
(5 + 2, B_11 as u8),
(2 + 1, B_1 as u8),
(1 + 2, B_11 as u8),
(2 + 4, B_1011 as u8),
(1 + 3, B_101 as u8),
(1 + 2, B_11 as u8),
(2 + 2, B_11 as u8),
(2 + 2, B_11 as u8),
(3 + 3, B_101 as u8),
(2 + 3, B_101 as u8),
(2 + 1, B_1 as u8),
(1 + 3, B_111 as u8),
(2 + 3, B_101 as u8),
( 2, B_11 as u8),
(3 + 1, B_1 as u8),
];

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