// Copyright 2018 The BoringSSL Authors

//

// Licensed under the Apache License, Version 2.0 (the "License");

// you may not use this file except in compliance with the License.

// You may obtain a copy of the License at

//

//     https://www.apache.org/licenses/LICENSE-2.0

//

// Unless required by applicable law or agreed to in writing, software

// distributed under the License is distributed on an "AS IS" BASIS,

// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

// See the License for the specific language governing permissions and

// limitations under the License.

#include <openssl/ec.h>

#include <openssl/err.h>

#include <openssl/mem.h>

#include <assert.h>

#include "internal.h"

#include "../bn/internal.h"

#include "../../internal.h"

const EC_FELEM *ec_felem_one(const EC_GROUP *group) {

  // We reuse generator.Z as a cache for 1 in the field.

  return &group->generator.raw.Z;

}

int ec_bignum_to_felem(const EC_GROUP *group, EC_FELEM *out, const BIGNUM *in) {

  uint8_t bytes[EC_MAX_BYTES];

  size_t len = BN_num_bytes(&group->field.N);

  assert(sizeof(bytes) >= len);

  if (BN_is_negative(in) || BN_cmp(in, &group->field.N) >= 0 ||

      !BN_bn2bin_padded(bytes, len, in)) {

    OPENSSL_PUT_ERROR(EC, EC_R_COORDINATES_OUT_OF_RANGE);

    return 0;

  }

  return ec_felem_from_bytes(group, out, bytes, len);

}

int ec_felem_to_bignum(const EC_GROUP *group, BIGNUM *out, const EC_FELEM *in) {

  uint8_t bytes[EC_MAX_BYTES];

  size_t len;

  ec_felem_to_bytes(group, bytes, &len, in);

  return BN_bin2bn(bytes, len, out) != nullptr;

}

void ec_felem_to_bytes(const EC_GROUP *group, uint8_t *out, size_t *out_len,

                       const EC_FELEM *in) {

  group->meth->felem_to_bytes(group, out, out_len, in);

}

int ec_felem_from_bytes(const EC_GROUP *group, EC_FELEM *out, const uint8_t *in,

                        size_t len) {

  return group->meth->felem_from_bytes(group, out, in, len);

}

void ec_felem_neg(const EC_GROUP *group, EC_FELEM *out, const EC_FELEM *a) {

  // -a is zero if a is zero and p-a otherwise.

  BN_ULONG mask = ec_felem_non_zero_mask(group, a);

  BN_ULONG borrow = bn_sub_words(out->words, group->field.N.d, a->words,

                                 group->field.N.width);

  assert(borrow == 0);

  (void)borrow;

  for (int i = 0; i < group->field.N.width; i++) {

    out->words[i] &= mask;

  }

}

void ec_felem_add(const EC_GROUP *group, EC_FELEM *out, const EC_FELEM *a,

                  const EC_FELEM *b) {

  EC_FELEM tmp;

  bn_mod_add_words(out->words, a->words, b->words, group->field.N.d, tmp.words,

                   group->field.N.width);

}

void ec_felem_sub(const EC_GROUP *group, EC_FELEM *out, const EC_FELEM *a,

                  const EC_FELEM *b) {

  EC_FELEM tmp;

  bn_mod_sub_words(out->words, a->words, b->words, group->field.N.d, tmp.words,

                   group->field.N.width);

}

BN_ULONG ec_felem_non_zero_mask(const EC_GROUP *group, const EC_FELEM *a) {

  BN_ULONG mask = 0;

  for (int i = 0; i < group->field.N.width; i++) {

    mask |= a->words[i];

  }

  return ~constant_time_is_zero_w(mask);

}

void ec_felem_select(const EC_GROUP *group, EC_FELEM *out, BN_ULONG mask,

                     const EC_FELEM *a, const EC_FELEM *b) {

  bn_select_words(out->words, mask, a->words, b->words, group->field.N.width);

}

int ec_felem_equal(const EC_GROUP *group, const EC_FELEM *a,

                   const EC_FELEM *b) {

  return CRYPTO_memcmp(a->words, b->words,

                       group->field.N.width * sizeof(BN_ULONG)) == 0;

}