// 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 <string.h>

#include <openssl/err.h>

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

#include "../bcm_interface.h"

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

#include "internal.h"

using namespace bssl;

int BN_rand(BIGNUM *rnd, int bits, int top, int bottom) {

  if (rnd == nullptr) {

    return 0;

  }

  if (top != BN_RAND_TOP_ANY && top != BN_RAND_TOP_ONE &&

      top != BN_RAND_TOP_TWO) {

    OPENSSL_PUT_ERROR(BN, ERR_R_SHOULD_NOT_HAVE_BEEN_CALLED);

    return 0;

  }

  if (bottom != BN_RAND_BOTTOM_ANY && bottom != BN_RAND_BOTTOM_ODD) {

    OPENSSL_PUT_ERROR(BN, ERR_R_SHOULD_NOT_HAVE_BEEN_CALLED);

    return 0;

  }

  if (bits == 0) {

    BN_zero(rnd);

    return 1;

  }

  if (bits > INT_MAX - (BN_BITS2 - 1)) {

    OPENSSL_PUT_ERROR(BN, BN_R_BIGNUM_TOO_LONG);

    return 0;

  }

  int words = (bits + BN_BITS2 - 1) / BN_BITS2;

  int bit = (bits - 1) % BN_BITS2;

  const BN_ULONG kOne = 1;

  const BN_ULONG kThree = 3;

  BN_ULONG mask = bit < BN_BITS2 - 1 ? (kOne << (bit + 1)) - 1 : BN_MASK2;

  if (!bn_wexpand(rnd, words)) {

    return 0;

  }

  FIPS_service_indicator_lock_state();

  BCM_rand_bytes((uint8_t *)rnd->d, words * sizeof(BN_ULONG));

  FIPS_service_indicator_unlock_state();

  rnd->d[words - 1] &= mask;

  if (top != BN_RAND_TOP_ANY) {

    if (top == BN_RAND_TOP_TWO && bits > 1) {

      if (bit == 0) {

        rnd->d[words - 1] |= 1;

        rnd->d[words - 2] |= kOne << (BN_BITS2 - 1);

      } else {

        rnd->d[words - 1] |= kThree << (bit - 1);

      }

    } else {

      rnd->d[words - 1] |= kOne << bit;

    }

  }

  if (bottom == BN_RAND_BOTTOM_ODD) {

    rnd->d[0] |= 1;

  }

  rnd->neg = 0;

  rnd->width = words;

  return 1;

}

int BN_pseudo_rand(BIGNUM *rnd, int bits, int top, int bottom) {

  return BN_rand(rnd, bits, top, bottom);

}

// bn_less_than_word_mask returns a mask of all ones if the number represented

// by |len| words at |a| is less than |b| and zero otherwise. It performs this

// computation in time independent of the value of |a|. |b| is assumed public.

static crypto_word_t bn_less_than_word_mask(const BN_ULONG *a, size_t len,

                                            BN_ULONG b) {

  if (b == 0) {

    return CONSTTIME_FALSE_W;

  }

  if (len == 0) {

    return CONSTTIME_TRUE_W;

  }

  // |a| < |b| iff a[1..len-1] are all zero and a[0] < b.

  static_assert(sizeof(BN_ULONG) <= sizeof(crypto_word_t),

                "crypto_word_t is too small");

  crypto_word_t mask = 0;

  for (size_t i = 1; i < len; i++) {

    mask |= a[i];

  }

  // |mask| is now zero iff a[1..len-1] are all zero.

  mask = constant_time_is_zero_w(mask);

  mask &= constant_time_lt_w(a[0], b);

  return mask;

}

int bssl::bn_in_range_words(const BN_ULONG *a, BN_ULONG min_inclusive,

                            const BN_ULONG *max_exclusive, size_t len) {

  crypto_word_t mask = ~bn_less_than_word_mask(a, len, min_inclusive);

  return mask & bn_less_than_words(a, max_exclusive, len);

}

static int bn_range_to_mask(size_t *out_words, BN_ULONG *out_mask,

                            size_t min_inclusive, const BN_ULONG *max_exclusive,

                            size_t len) {

  // The magnitude of |max_exclusive| is assumed public.

  size_t words = len;

  while (words > 0 && max_exclusive[words - 1] == 0) {

    words--;

  }

  if (words == 0 || (words == 1 && max_exclusive[0] <= min_inclusive)) {

    OPENSSL_PUT_ERROR(BN, BN_R_INVALID_RANGE);

    return 0;

  }

  BN_ULONG mask = max_exclusive[words - 1];

  // This sets all bits in |mask| below the most significant bit.

  mask |= mask >> 1;

  mask |= mask >> 2;

  mask |= mask >> 4;

  mask |= mask >> 8;

  mask |= mask >> 16;

#if defined(OPENSSL_64_BIT)

  mask |= mask >> 32;

#endif

  *out_words = words;

  *out_mask = mask;

  return 1;

}

int bssl::bn_rand_range_words(BN_ULONG *out, BN_ULONG min_inclusive,

                              const BN_ULONG *max_exclusive, size_t len,

                              const uint8_t additional_data[32]) {

  // This function implements the equivalent of steps 1 through 4 of FIPS 186-5

  // appendices A.2.2 and A.3.2, repeating the process on failure. When called

  // in those contexts, |max_exclusive| is n and |min_inclusive| is one.

  // Compute the bit length of |max_exclusive| (step 1), in terms of a number of

  // |words| worth of entropy to fill and a mask of bits to clear in the top

  // word.

  size_t words;

  BN_ULONG mask;

  if (!bn_range_to_mask(&words, &mask, min_inclusive, max_exclusive, len)) {

    return 0;

  }

  // Fill any unused words with zero.

  OPENSSL_memset(out + words, 0, (len - words) * sizeof(BN_ULONG));

  unsigned count = 100;

  do {

    if (!--count) {

      OPENSSL_PUT_ERROR(BN, BN_R_TOO_MANY_ITERATIONS);

      return 0;

    }

    // Use |words| and |mask| together to obtain a string of N bits, where N is

    // the bit length of |max_exclusive|.

    FIPS_service_indicator_lock_state();

    BCM_rand_bytes_with_additional_data(

        (uint8_t *)out, words * sizeof(BN_ULONG), additional_data);

    FIPS_service_indicator_unlock_state();

    out[words - 1] &= mask;

    // If out >= max_exclusive or out < min_inclusive, retry. The result of this

    // comparison may be treated as public. It only reveals how many attempts

    // were needed before we found a value in range. This is independent of the

    // final secret output, and has a distribution that depends only on

    // |min_inclusive| and |max_exclusive|, both of which are public.

  } while (!constant_time_declassify_int(

      bn_in_range_words(out, min_inclusive, max_exclusive, words)));

  return 1;

}

int BN_rand_range_ex(BIGNUM *r, BN_ULONG min_inclusive,

                     const BIGNUM *max_exclusive) {

  static const uint8_t kDefaultAdditionalData[32] = {0};

  if (!bn_wexpand(r, max_exclusive->width) ||

      !bn_rand_range_words(r->d, min_inclusive, max_exclusive->d,

                           max_exclusive->width, kDefaultAdditionalData)) {

    return 0;

  }

  r->neg = 0;

  r->width = max_exclusive->width;

  return 1;

}

int bssl::bn_rand_secret_range(BIGNUM *r, int *out_is_uniform,

                               BN_ULONG min_inclusive,

                               const BIGNUM *max_exclusive) {

  size_t words;

  BN_ULONG mask;

  if (!bn_range_to_mask(&words, &mask, min_inclusive, max_exclusive->d,

                        max_exclusive->width) ||

      !bn_wexpand(r, words)) {

    return 0;

  }

  assert(words > 0);

  assert(mask != 0);

  // The range must be large enough for bit tricks to fix invalid values.

  if (words == 1 && min_inclusive > mask >> 1) {

    OPENSSL_PUT_ERROR(BN, BN_R_INVALID_RANGE);

    return 0;

  }

  // Select a uniform random number with num_bits(max_exclusive) bits.

  FIPS_service_indicator_lock_state();

  BCM_rand_bytes((uint8_t *)r->d, words * sizeof(BN_ULONG));

  FIPS_service_indicator_unlock_state();

  r->d[words - 1] &= mask;

  // Check, in constant-time, if the value is in range.

  *out_is_uniform =

      bn_in_range_words(r->d, min_inclusive, max_exclusive->d, words);

  crypto_word_t in_range = *out_is_uniform;

  in_range = 0 - in_range;

  // If the value is not in range, force it to be in range.

  r->d[0] |= constant_time_select_w(in_range, 0, min_inclusive);

  r->d[words - 1] &= constant_time_select_w(in_range, BN_MASK2, mask >> 1);

  declassify_assert(

      bn_in_range_words(r->d, min_inclusive, max_exclusive->d, words));

  r->neg = 0;

  r->width = (int)words;

  return 1;

}

int BN_rand_range(BIGNUM *r, const BIGNUM *range) {

  return BN_rand_range_ex(r, 0, range);

}

int BN_pseudo_rand_range(BIGNUM *r, const BIGNUM *range) {

  return BN_rand_range(r, range);

}