ffbf95ad41
Now that the tuned add/dbl implementations are exposed, these can be specific to EC_GFp_mont_method and call the felem_mul and felem_sqr implementations directly. felem_sqr and felem_mul are still used elsewhere in simple.c, however, so we cannot get rid of them yet. Change-Id: I5ea22a8815279931afc98a6fc578bc85e3f8bdcc Reviewed-on: https://boringssl-review.googlesource.com/c/32849 Commit-Queue: David Benjamin <davidben@google.com> CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org> Reviewed-by: Adam Langley <agl@google.com>
100 lines
3.9 KiB
C
100 lines
3.9 KiB
C
/* Copyright (c) 2018, Google Inc.
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*
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* Permission to use, copy, modify, and/or distribute this software for any
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* purpose with or without fee is hereby granted, provided that the above
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* copyright notice and this permission notice appear in all copies.
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*
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* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
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* SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
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* OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
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* CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
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#include <openssl/ec.h>
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#include <assert.h>
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#include "internal.h"
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#include "../bn/internal.h"
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#include "../../internal.h"
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static void ec_GFp_mont_mul_single(const EC_GROUP *group, EC_RAW_POINT *r,
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const EC_RAW_POINT *p,
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const EC_SCALAR *scalar) {
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// This is a generic implementation for uncommon curves that not do not
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// warrant a tuned one. It uses unsigned digits so that the doubling case in
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// |ec_GFp_mont_add| is always unreachable, erring on safety and simplicity.
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// Compute a table of the first 32 multiples of |p| (including infinity).
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EC_RAW_POINT precomp[32];
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ec_GFp_simple_point_set_to_infinity(group, &precomp[0]);
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ec_GFp_simple_point_copy(&precomp[1], p);
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for (size_t j = 2; j < OPENSSL_ARRAY_SIZE(precomp); j++) {
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if (j & 1) {
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ec_GFp_mont_add(group, &precomp[j], &precomp[1], &precomp[j - 1]);
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} else {
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ec_GFp_mont_dbl(group, &precomp[j], &precomp[j / 2]);
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}
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}
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// Divide bits in |scalar| into windows.
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unsigned bits = BN_num_bits(&group->order);
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int r_is_at_infinity = 1;
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for (unsigned i = bits - 1; i < bits; i--) {
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if (!r_is_at_infinity) {
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ec_GFp_mont_dbl(group, r, r);
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}
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if (i % 5 == 0) {
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// Compute the next window value.
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const size_t width = group->order.width;
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uint8_t window = bn_is_bit_set_words(scalar->words, width, i + 4) << 4;
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window |= bn_is_bit_set_words(scalar->words, width, i + 3) << 3;
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window |= bn_is_bit_set_words(scalar->words, width, i + 2) << 2;
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window |= bn_is_bit_set_words(scalar->words, width, i + 1) << 1;
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window |= bn_is_bit_set_words(scalar->words, width, i);
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// Select the entry in constant-time.
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EC_RAW_POINT tmp;
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OPENSSL_memset(&tmp, 0, sizeof(EC_RAW_POINT));
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for (size_t j = 0; j < OPENSSL_ARRAY_SIZE(precomp); j++) {
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BN_ULONG mask = constant_time_eq_w(j, window);
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ec_felem_select(group, &tmp.X, mask, &precomp[j].X, &tmp.X);
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ec_felem_select(group, &tmp.Y, mask, &precomp[j].Y, &tmp.Y);
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ec_felem_select(group, &tmp.Z, mask, &precomp[j].Z, &tmp.Z);
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}
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if (r_is_at_infinity) {
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ec_GFp_simple_point_copy(r, &tmp);
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r_is_at_infinity = 0;
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} else {
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ec_GFp_mont_add(group, r, r, &tmp);
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}
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}
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}
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if (r_is_at_infinity) {
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ec_GFp_simple_point_set_to_infinity(group, r);
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}
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}
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void ec_GFp_mont_mul(const EC_GROUP *group, EC_RAW_POINT *r,
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const EC_SCALAR *g_scalar, const EC_RAW_POINT *p,
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const EC_SCALAR *p_scalar) {
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assert(g_scalar != NULL || p_scalar != NULL);
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if (p_scalar == NULL) {
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ec_GFp_mont_mul_single(group, r, &group->generator->raw, g_scalar);
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} else if (g_scalar == NULL) {
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ec_GFp_mont_mul_single(group, r, p, p_scalar);
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} else {
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// Support constant-time two-point multiplication for compatibility. This
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// does not actually come up in keygen, ECDH, or ECDSA, so we implement it
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// the naive way.
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ec_GFp_mont_mul_single(group, r, &group->generator->raw, g_scalar);
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EC_RAW_POINT tmp;
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ec_GFp_mont_mul_single(group, &tmp, p, p_scalar);
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ec_GFp_mont_add(group, r, r, &tmp);
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}
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}
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