1/* Copyright 2018 The BoringSSL Authors 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 26const EC_FELEM *ec_felem_one(const EC_GROUP *group) { 27 // We reuse generator.Z as a cache for 1 in the field. 28 return &group->generator.raw.Z; 29} 30 31int ec_bignum_to_felem(const EC_GROUP *group, EC_FELEM *out, const BIGNUM *in) { 32 uint8_t bytes[EC_MAX_BYTES]; 33 size_t len = BN_num_bytes(&group->field.N); 34 assert(sizeof(bytes) >= len); 35 if (BN_is_negative(in) || BN_cmp(in, &group->field.N) >= 0 || 36 !BN_bn2bin_padded(bytes, len, in)) { 37 OPENSSL_PUT_ERROR(EC, EC_R_COORDINATES_OUT_OF_RANGE); 38 return 0; 39 } 40 41 return ec_felem_from_bytes(group, out, bytes, len); 42} 43 44int ec_felem_to_bignum(const EC_GROUP *group, BIGNUM *out, const EC_FELEM *in) { 45 uint8_t bytes[EC_MAX_BYTES]; 46 size_t len; 47 ec_felem_to_bytes(group, bytes, &len, in); 48 return BN_bin2bn(bytes, len, out) != NULL; 49} 50 51void ec_felem_to_bytes(const EC_GROUP *group, uint8_t *out, size_t *out_len, 52 const EC_FELEM *in) { 53 group->meth->felem_to_bytes(group, out, out_len, in); 54} 55 56int ec_felem_from_bytes(const EC_GROUP *group, EC_FELEM *out, const uint8_t *in, 57 size_t len) { 58 return group->meth->felem_from_bytes(group, out, in, len); 59} 60 61void ec_felem_neg(const EC_GROUP *group, EC_FELEM *out, const EC_FELEM *a) { 62 // -a is zero if a is zero and p-a otherwise. 63 BN_ULONG mask = ec_felem_non_zero_mask(group, a); 64 BN_ULONG borrow = bn_sub_words(out->words, group->field.N.d, a->words, 65 group->field.N.width); 66 assert(borrow == 0); 67 (void)borrow; 68 for (int i = 0; i < group->field.N.width; i++) { 69 out->words[i] &= mask; 70 } 71} 72 73void ec_felem_add(const EC_GROUP *group, EC_FELEM *out, const EC_FELEM *a, 74 const EC_FELEM *b) { 75 EC_FELEM tmp; 76 bn_mod_add_words(out->words, a->words, b->words, group->field.N.d, tmp.words, 77 group->field.N.width); 78} 79 80void ec_felem_sub(const EC_GROUP *group, EC_FELEM *out, const EC_FELEM *a, 81 const EC_FELEM *b) { 82 EC_FELEM tmp; 83 bn_mod_sub_words(out->words, a->words, b->words, group->field.N.d, tmp.words, 84 group->field.N.width); 85} 86 87BN_ULONG ec_felem_non_zero_mask(const EC_GROUP *group, const EC_FELEM *a) { 88 BN_ULONG mask = 0; 89 for (int i = 0; i < group->field.N.width; i++) { 90 mask |= a->words[i]; 91 } 92 return ~constant_time_is_zero_w(mask); 93} 94 95void ec_felem_select(const EC_GROUP *group, EC_FELEM *out, BN_ULONG mask, 96 const EC_FELEM *a, const EC_FELEM *b) { 97 bn_select_words(out->words, mask, a->words, b->words, group->field.N.width); 98} 99 100int ec_felem_equal(const EC_GROUP *group, const EC_FELEM *a, 101 const EC_FELEM *b) { 102 return CRYPTO_memcmp(a->words, b->words, 103 group->field.N.width * sizeof(BN_ULONG)) == 0; 104} 105