1 /* Copyright (c) 2018, Google Inc.
2 *
3 * Permission to use, copy, modify, and/or distribute this software for any
4 * purpose with or without fee is hereby granted, provided that the above
5 * copyright notice and this permission notice appear in all copies.
6 *
7 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
8 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
9 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
10 * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
11 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
12 * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
13 * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
14
15 #include <openssl/ec.h>
16 #include <openssl/err.h>
17
18 #include <assert.h>
19
20 #include "internal.h"
21 #include "../bn/internal.h"
22 #include "../../internal.h"
23
24
ec_bignum_to_felem(const EC_GROUP * group,EC_FELEM * out,const BIGNUM * in)25 int ec_bignum_to_felem(const EC_GROUP *group, EC_FELEM *out, const BIGNUM *in) {
26 if (BN_is_negative(in) || BN_cmp(in, &group->field) >= 0) {
27 OPENSSL_PUT_ERROR(EC, EC_R_COORDINATES_OUT_OF_RANGE);
28 return 0;
29 }
30 return group->meth->bignum_to_felem(group, out, in);
31 }
32
ec_felem_to_bignum(const EC_GROUP * group,BIGNUM * out,const EC_FELEM * in)33 int ec_felem_to_bignum(const EC_GROUP *group, BIGNUM *out, const EC_FELEM *in) {
34 return group->meth->felem_to_bignum(group, out, in);
35 }
36
ec_felem_neg(const EC_GROUP * group,EC_FELEM * out,const EC_FELEM * a)37 void ec_felem_neg(const EC_GROUP *group, EC_FELEM *out, const EC_FELEM *a) {
38 // -a is zero if a is zero and p-a otherwise.
39 BN_ULONG mask = ec_felem_non_zero_mask(group, a);
40 BN_ULONG borrow =
41 bn_sub_words(out->words, group->field.d, a->words, group->field.width);
42 assert(borrow == 0);
43 (void)borrow;
44 for (int i = 0; i < group->field.width; i++) {
45 out->words[i] &= mask;
46 }
47 }
48
ec_felem_add(const EC_GROUP * group,EC_FELEM * out,const EC_FELEM * a,const EC_FELEM * b)49 void ec_felem_add(const EC_GROUP *group, EC_FELEM *out, const EC_FELEM *a,
50 const EC_FELEM *b) {
51 EC_FELEM tmp;
52 bn_mod_add_words(out->words, a->words, b->words, group->field.d, tmp.words,
53 group->field.width);
54 }
55
ec_felem_sub(const EC_GROUP * group,EC_FELEM * out,const EC_FELEM * a,const EC_FELEM * b)56 void ec_felem_sub(const EC_GROUP *group, EC_FELEM *out, const EC_FELEM *a,
57 const EC_FELEM *b) {
58 EC_FELEM tmp;
59 bn_mod_sub_words(out->words, a->words, b->words, group->field.d, tmp.words,
60 group->field.width);
61 }
62
ec_felem_non_zero_mask(const EC_GROUP * group,const EC_FELEM * a)63 BN_ULONG ec_felem_non_zero_mask(const EC_GROUP *group, const EC_FELEM *a) {
64 BN_ULONG mask = 0;
65 for (int i = 0; i < group->field.width; i++) {
66 mask |= a->words[i];
67 }
68 return ~constant_time_is_zero_w(mask);
69 }
70
ec_felem_select(const EC_GROUP * group,EC_FELEM * out,BN_ULONG mask,const EC_FELEM * a,const EC_FELEM * b)71 void ec_felem_select(const EC_GROUP *group, EC_FELEM *out, BN_ULONG mask,
72 const EC_FELEM *a, const EC_FELEM *b) {
73 bn_select_words(out->words, mask, a->words, b->words, group->field.width);
74 }
75
ec_felem_equal(const EC_GROUP * group,const EC_FELEM * a,const EC_FELEM * b)76 int ec_felem_equal(const EC_GROUP *group, const EC_FELEM *a,
77 const EC_FELEM *b) {
78 // Note this function is variable-time. Constant-time operations should use
79 // |ec_felem_non_zero_mask|.
80 return OPENSSL_memcmp(a->words, b->words,
81 group->field.width * sizeof(BN_ULONG)) == 0;
82 }
83