// Copyright 1995-2016 The OpenSSL Project Authors. All Rights Reserved.

//

// 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/bn.h>

#include <assert.h>

#include <limits.h>

#include "internal.h"

void bn_big_endian_to_words(BN_ULONG *out, size_t out_len, const uint8_t *in,

                            size_t in_len) {

  // The caller should have sized |out| to fit |in| without truncating. This

  // condition ensures we do not overflow |out|, so use a runtime check.

  BSSL_CHECK(in_len <= out_len * sizeof(BN_ULONG));

  // Load whole words.

  while (in_len >= sizeof(BN_ULONG)) {

    in_len -= sizeof(BN_ULONG);

    out[0] = CRYPTO_load_word_be(in + in_len);

    out++;

    out_len--;

  }

  // Load the last partial word.

  if (in_len != 0) {

    BN_ULONG word = 0;

    for (size_t i = 0; i < in_len; i++) {

      word = (word << 8) | in[i];

    }

    out[0] = word;

    out++;

    out_len--;

  }

  // Fill the remainder with zeros.

  OPENSSL_memset(out, 0, out_len * sizeof(BN_ULONG));

}

BIGNUM *BN_bin2bn(const uint8_t *in, size_t len, BIGNUM *ret) {

  BIGNUM *bn = NULL;

  if (ret == NULL) {

    bn = BN_new();

    if (bn == NULL) {

      return NULL;

    }

    ret = bn;

  }

  if (len == 0) {

    ret->width = 0;

    return ret;

  }

  size_t num_words = ((len - 1) / BN_BYTES) + 1;

  if (!bn_wexpand(ret, num_words)) {

    BN_free(bn);

    return NULL;

  }

  // |bn_wexpand| must check bounds on |num_words| to write it into

  // |ret->dmax|.

  assert(num_words <= INT_MAX);

  ret->width = (int)num_words;

  ret->neg = 0;

  bn_big_endian_to_words(ret->d, ret->width, in, len);

  return ret;

}

BIGNUM *BN_lebin2bn(const uint8_t *in, size_t len, BIGNUM *ret) {

  BIGNUM *bn = NULL;

  if (ret == NULL) {

    bn = BN_new();

    if (bn == NULL) {

      return NULL;

    }

    ret = bn;

  }

  if (len == 0) {

    ret->width = 0;

    ret->neg = 0;

    return ret;

  }

  // Reserve enough space in |ret|.

  size_t num_words = ((len - 1) / BN_BYTES) + 1;

  if (!bn_wexpand(ret, num_words)) {

    BN_free(bn);

    return NULL;

  }

  ret->width = (int)num_words;

  // Make sure the top bytes will be zeroed.

  ret->d[num_words - 1] = 0;

  // We only support little-endian platforms, so we can simply memcpy the

  // internal representation.

  OPENSSL_memcpy(ret->d, in, len);

  return ret;

}

BIGNUM *BN_le2bn(const uint8_t *in, size_t len, BIGNUM *ret) {

  return BN_lebin2bn(in, len, ret);

}

// fits_in_bytes returns one if the |num_words| words in |words| can be

// represented in |num_bytes| bytes.

static int fits_in_bytes(const BN_ULONG *words, size_t num_words,

                         size_t num_bytes) {

  const uint8_t *bytes = (const uint8_t *)words;

  size_t tot_bytes = num_words * sizeof(BN_ULONG);

  uint8_t mask = 0;

  for (size_t i = num_bytes; i < tot_bytes; i++) {

    mask |= bytes[i];

  }

  return mask == 0;

}

void bn_assert_fits_in_bytes(const BIGNUM *bn, size_t num) {

  const uint8_t *bytes = (const uint8_t *)bn->d;

  size_t tot_bytes = bn->width * sizeof(BN_ULONG);

  if (tot_bytes > num) {

    CONSTTIME_DECLASSIFY(bytes + num, tot_bytes - num);

    for (size_t i = num; i < tot_bytes; i++) {

      assert(bytes[i] == 0);

    }

    (void)bytes;

  }

}

void bn_words_to_big_endian(uint8_t *out, size_t out_len, const BN_ULONG *in,

                            size_t in_len) {

  // The caller should have selected an output length without truncation.

  declassify_assert(fits_in_bytes(in, in_len, out_len));

  // We only support little-endian platforms, so the internal representation is

  // also little-endian as bytes. We can simply copy it in reverse.

  const uint8_t *bytes = (const uint8_t *)in;

  size_t num_bytes = in_len * sizeof(BN_ULONG);

  if (out_len < num_bytes) {

    num_bytes = out_len;

  }

  for (size_t i = 0; i < num_bytes; i++) {

    out[out_len - i - 1] = bytes[i];

  }

  // Pad out the rest of the buffer with zeroes.

  OPENSSL_memset(out, 0, out_len - num_bytes);

}

size_t BN_bn2bin(const BIGNUM *in, uint8_t *out) {

  size_t n = BN_num_bytes(in);

  bn_words_to_big_endian(out, n, in->d, in->width);

  return n;

}

int BN_bn2le_padded(uint8_t *out, size_t len, const BIGNUM *in) {

  if (!fits_in_bytes(in->d, in->width, len)) {

    return 0;

  }

  // We only support little-endian platforms, so we can simply memcpy into the

  // internal representation.

  const uint8_t *bytes = (const uint8_t *)in->d;

  size_t num_bytes = in->width * BN_BYTES;

  if (len < num_bytes) {

    num_bytes = len;

  }

  OPENSSL_memcpy(out, bytes, num_bytes);

  // Pad out the rest of the buffer with zeroes.

  OPENSSL_memset(out + num_bytes, 0, len - num_bytes);

  return 1;

}

int BN_bn2bin_padded(uint8_t *out, size_t len, const BIGNUM *in) {

  if (!fits_in_bytes(in->d, in->width, len)) {

    return 0;

  }

  bn_words_to_big_endian(out, len, in->d, in->width);

  return 1;

}

BN_ULONG BN_get_word(const BIGNUM *bn) {

  switch (bn_minimal_width(bn)) {

    case 0:

      return 0;

    case 1:

      return bn->d[0];

    default:

      return BN_MASK2;

  }

}

int BN_get_u64(const BIGNUM *bn, uint64_t *out) {

  switch (bn_minimal_width(bn)) {

    case 0:

      *out = 0;

      return 1;

    case 1:

      *out = bn->d[0];

      return 1;

#if defined(OPENSSL_32_BIT)

    case 2:

      *out = (uint64_t) bn->d[0] | (((uint64_t) bn->d[1]) << 32);

      return 1;

#endif

    default:

      return 0;

  }

}