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 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 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 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 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 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 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 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 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
