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 #include <openssl/mem.h>
18
19 #include <assert.h>
20
21 #include "internal.h"
22 #include "../bn/internal.h"
23 #include "../../internal.h"
24
25
ec_bignum_to_felem(const EC_GROUP * group,EC_FELEM * out,const BIGNUM * in)26 int ec_bignum_to_felem(const EC_GROUP *group, EC_FELEM *out, const BIGNUM *in) {
27 uint8_t bytes[EC_MAX_BYTES];
28 size_t len = BN_num_bytes(&group->field);
29 assert(sizeof(bytes) >= len);
30 if (BN_is_negative(in) ||
31 BN_cmp(in, &group->field) >= 0 ||
32 !BN_bn2bin_padded(bytes, len, in)) {
33 OPENSSL_PUT_ERROR(EC, EC_R_COORDINATES_OUT_OF_RANGE);
34 return 0;
35 }
36
37 return ec_felem_from_bytes(group, out, bytes, len);
38 }
39
ec_felem_to_bignum(const EC_GROUP * group,BIGNUM * out,const EC_FELEM * in)40 int ec_felem_to_bignum(const EC_GROUP *group, BIGNUM *out, const EC_FELEM *in) {
41 uint8_t bytes[EC_MAX_BYTES];
42 size_t len;
43 ec_felem_to_bytes(group, bytes, &len, in);
44 return BN_bin2bn(bytes, len, out) != NULL;
45 }
46
ec_felem_to_bytes(const EC_GROUP * group,uint8_t * out,size_t * out_len,const EC_FELEM * in)47 void ec_felem_to_bytes(const EC_GROUP *group, uint8_t *out, size_t *out_len,
48 const EC_FELEM *in) {
49 group->meth->felem_to_bytes(group, out, out_len, in);
50 }
51
ec_felem_from_bytes(const EC_GROUP * group,EC_FELEM * out,const uint8_t * in,size_t len)52 int ec_felem_from_bytes(const EC_GROUP *group, EC_FELEM *out, const uint8_t *in,
53 size_t len) {
54 return group->meth->felem_from_bytes(group, out, in, len);
55 }
56
ec_felem_neg(const EC_GROUP * group,EC_FELEM * out,const EC_FELEM * a)57 void ec_felem_neg(const EC_GROUP *group, EC_FELEM *out, const EC_FELEM *a) {
58 // -a is zero if a is zero and p-a otherwise.
59 BN_ULONG mask = ec_felem_non_zero_mask(group, a);
60 BN_ULONG borrow =
61 bn_sub_words(out->words, group->field.d, a->words, group->field.width);
62 assert(borrow == 0);
63 (void)borrow;
64 for (int i = 0; i < group->field.width; i++) {
65 out->words[i] &= mask;
66 }
67 }
68
ec_felem_add(const EC_GROUP * group,EC_FELEM * out,const EC_FELEM * a,const EC_FELEM * b)69 void ec_felem_add(const EC_GROUP *group, EC_FELEM *out, const EC_FELEM *a,
70 const EC_FELEM *b) {
71 EC_FELEM tmp;
72 bn_mod_add_words(out->words, a->words, b->words, group->field.d, tmp.words,
73 group->field.width);
74 }
75
ec_felem_sub(const EC_GROUP * group,EC_FELEM * out,const EC_FELEM * a,const EC_FELEM * b)76 void ec_felem_sub(const EC_GROUP *group, EC_FELEM *out, const EC_FELEM *a,
77 const EC_FELEM *b) {
78 EC_FELEM tmp;
79 bn_mod_sub_words(out->words, a->words, b->words, group->field.d, tmp.words,
80 group->field.width);
81 }
82
ec_felem_non_zero_mask(const EC_GROUP * group,const EC_FELEM * a)83 BN_ULONG ec_felem_non_zero_mask(const EC_GROUP *group, const EC_FELEM *a) {
84 BN_ULONG mask = 0;
85 for (int i = 0; i < group->field.width; i++) {
86 mask |= a->words[i];
87 }
88 return ~constant_time_is_zero_w(mask);
89 }
90
ec_felem_select(const EC_GROUP * group,EC_FELEM * out,BN_ULONG mask,const EC_FELEM * a,const EC_FELEM * b)91 void ec_felem_select(const EC_GROUP *group, EC_FELEM *out, BN_ULONG mask,
92 const EC_FELEM *a, const EC_FELEM *b) {
93 bn_select_words(out->words, mask, a->words, b->words, group->field.width);
94 }
95
ec_felem_equal(const EC_GROUP * group,const EC_FELEM * a,const EC_FELEM * b)96 int ec_felem_equal(const EC_GROUP *group, const EC_FELEM *a,
97 const EC_FELEM *b) {
98 return CRYPTO_memcmp(a->words, b->words,
99 group->field.width * sizeof(BN_ULONG)) == 0;
100 }
101