fipsmodule/bn/random.c

/* Copyright (C) 1995-1998 Eric Young ([email protected])
 * All rights reserved.
 *
 * This package is an SSL implementation written
 * by Eric Young ([email protected]).
 * The implementation was written so as to conform with Netscapes SSL.
 *
 * This library is free for commercial and non-commercial use as long as
 * the following conditions are aheared to.  The following conditions
 * apply to all code found in this distribution, be it the RC4, RSA,
 * lhash, DES, etc., code; not just the SSL code.  The SSL documentation
 * included with this distribution is covered by the same copyright terms
 * except that the holder is Tim Hudson ([email protected]).
 *
 * Copyright remains Eric Young's, and as such any Copyright notices in
 * the code are not to be removed.
 * If this package is used in a product, Eric Young should be given attribution
 * as the author of the parts of the library used.
 * This can be in the form of a textual message at program startup or
 * in documentation (online or textual) provided with the package.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *    "This product includes cryptographic software written by
 *     Eric Young ([email protected])"
 *    The word 'cryptographic' can be left out if the rouines from the library
 *    being used are not cryptographic related :-).
 * 4. If you include any Windows specific code (or a derivative thereof) from
 *    the apps directory (application code) you must include an acknowledgement:
 *    "This product includes software written by Tim Hudson ([email protected])"
 *
 * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * The licence and distribution terms for any publically available version or
 * derivative of this code cannot be changed.  i.e. this code cannot simply be
 * copied and put under another distribution licence
 * [including the GNU Public Licence.]
 */
/* ====================================================================
 * Copyright (c) 1998-2001 The OpenSSL Project.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. All advertising materials mentioning features or use of this
 *    software must display the following acknowledgment:
 *    "This product includes software developed by the OpenSSL Project
 *    for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
 *
 * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
 *    endorse or promote products derived from this software without
 *    prior written permission. For written permission, please contact
 *    [email protected].
 *
 * 5. Products derived from this software may not be called "OpenSSL"
 *    nor may "OpenSSL" appear in their names without prior written
 *    permission of the OpenSSL Project.
 *
 * 6. Redistributions of any form whatsoever must retain the following
 *    acknowledgment:
 *    "This product includes software developed by the OpenSSL Project
 *    for use in the OpenSSL Toolkit (http://www.openssl.org/)"
 *
 * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
 * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE OpenSSL PROJECT OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 * ====================================================================
 *
 * This product includes cryptographic software written by Eric Young
 * ([email protected]).  This product includes software written by Tim
 * Hudson ([email protected]). */

#include <openssl/bn.h>

#include <assert.h>
#include <limits.h>
#include <string.h>

#include <openssl/err.h>
#include <openssl/rand.h>

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


int BN_rand(BIGNUM *rnd, int bits, int top, int bottom) {
  if (rnd == NULL) {
    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();
  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 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 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 4 through 7 of FIPS 186-4
  // appendices B.4.2 and B.5.2. 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;
    }

    // Steps 4 and 5. 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();
    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. This implements
    // the equivalent of steps 6 and 7 without leaking the value of |out|. 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 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();
  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);
}