Coverage Report

Created: 2025-03-09 06:52

/src/libressl/crypto/bn/bn_recp.c
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Source (jump to first uncovered line)
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/* $OpenBSD: bn_recp.c,v 1.33 2025/02/04 20:22:20 tb Exp $ */
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/* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
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 * All rights reserved.
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 *
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 * This package is an SSL implementation written
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 * by Eric Young (eay@cryptsoft.com).
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 * The implementation was written so as to conform with Netscapes SSL.
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 *
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 * This library is free for commercial and non-commercial use as long as
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 * the following conditions are aheared to.  The following conditions
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 * apply to all code found in this distribution, be it the RC4, RSA,
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 * lhash, DES, etc., code; not just the SSL code.  The SSL documentation
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 * included with this distribution is covered by the same copyright terms
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 * except that the holder is Tim Hudson (tjh@cryptsoft.com).
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 *
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 * Copyright remains Eric Young's, and as such any Copyright notices in
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 * the code are not to be removed.
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 * If this package is used in a product, Eric Young should be given attribution
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 * as the author of the parts of the library used.
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 * This can be in the form of a textual message at program startup or
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 * in documentation (online or textual) provided with the package.
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 *
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 * Redistribution and use in source and binary forms, with or without
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 * modification, are permitted provided that the following conditions
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 * are met:
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 * 1. Redistributions of source code must retain the copyright
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 *    notice, this list of conditions and the following disclaimer.
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 * 2. Redistributions in binary form must reproduce the above copyright
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 *    notice, this list of conditions and the following disclaimer in the
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 *    documentation and/or other materials provided with the distribution.
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 * 3. All advertising materials mentioning features or use of this software
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 *    must display the following acknowledgement:
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 *    "This product includes cryptographic software written by
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 *     Eric Young (eay@cryptsoft.com)"
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 *    The word 'cryptographic' can be left out if the rouines from the library
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 *    being used are not cryptographic related :-).
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 * 4. If you include any Windows specific code (or a derivative thereof) from
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 *    the apps directory (application code) you must include an acknowledgement:
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 *    "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
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 *
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 * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
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 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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 * SUCH DAMAGE.
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 *
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 * The licence and distribution terms for any publically available version or
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 * derivative of this code cannot be changed.  i.e. this code cannot simply be
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 * copied and put under another distribution licence
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 * [including the GNU Public Licence.]
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 */
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#include <stdio.h>
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#include <openssl/err.h>
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#include "bn_local.h"
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struct bn_recp_ctx_st {
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  BIGNUM *N;  /* the divisor */
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  BIGNUM *Nr; /* the reciprocal 2^shift / N */
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  int num_bits; /* number of bits in N */
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  int shift;
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} /* BN_RECP_CTX */;
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BN_RECP_CTX *
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BN_RECP_CTX_create(const BIGNUM *N)
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922
{
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922
  BN_RECP_CTX *recp;
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922
  if ((recp = calloc(1, sizeof(*recp))) == NULL)
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0
    goto err;
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80
922
  if ((recp->N = BN_dup(N)) == NULL)
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0
    goto err;
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922
  BN_set_negative(recp->N, 0);
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922
  recp->num_bits = BN_num_bits(recp->N);
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85
922
  if ((recp->Nr = BN_new()) == NULL)
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0
    goto err;
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88
922
  return recp;
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90
0
 err:
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0
  BN_RECP_CTX_free(recp);
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93
0
  return NULL;
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922
}
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void
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BN_RECP_CTX_free(BN_RECP_CTX *recp)
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922
{
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922
  if (recp == NULL)
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0
    return;
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102
922
  BN_free(recp->N);
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922
  BN_free(recp->Nr);
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922
  freezero(recp, sizeof(*recp));
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922
}
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107
int
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BN_div_reciprocal(BIGNUM *dv, BIGNUM *rem, const BIGNUM *m, BN_RECP_CTX *recp,
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    BN_CTX *ctx)
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197k
{
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197k
  int i, j, ret = 0;
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197k
  BIGNUM *a, *b, *d, *r;
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114
197k
  if (BN_ucmp(m, recp->N) < 0) {
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12.7k
    if (dv != NULL)
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0
      BN_zero(dv);
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12.7k
    if (rem != NULL)
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12.7k
      return bn_copy(rem, m);
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0
    return 1;
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12.7k
  }
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122
184k
  BN_CTX_start(ctx);
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184k
  if ((a = BN_CTX_get(ctx)) == NULL)
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0
    goto err;
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184k
  if ((b = BN_CTX_get(ctx)) == NULL)
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0
    goto err;
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128
184k
  if ((d = dv) == NULL)
129
184k
    d = BN_CTX_get(ctx);
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184k
  if (d == NULL)
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0
    goto err;
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133
184k
  if ((r = rem) == NULL)
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0
    r = BN_CTX_get(ctx);
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184k
  if (r == NULL)
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0
    goto err;
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  /*
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   * We want the remainder. Given input of ABCDEF / ab we need to
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   * multiply ABCDEF by 3 digits of the reciprocal of ab.
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   */
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  /* i := max(BN_num_bits(m), 2*BN_num_bits(N)) */
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184k
  i = BN_num_bits(m);
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184k
  j = recp->num_bits << 1;
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184k
  if (j > i)
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169k
    i = j;
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  /* Compute Nr := (1 << i) / N if necessary. */
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184k
  if (i != recp->shift) {
151
851
    BN_zero(recp->Nr);
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851
    if (!BN_set_bit(recp->Nr, i))
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0
      goto err;
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851
    if (!BN_div_ct(recp->Nr, NULL, recp->Nr, recp->N, ctx))
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0
      goto err;
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851
    recp->shift = i;
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851
  }
158
159
  /*
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   * d := |((m >> BN_num_bits(N)) * recp->Nr)     >> (i - BN_num_bits(N))|
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   *    = |((m >> BN_num_bits(N)) * (1 << i) / N) >> (i - BN_num_bits(N))|
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   *   <= |(m / 2^BN_num_bits(N)) * (2^i / N) * 2^BN_num_bits(N) / 2^i |
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   *    = |m / N|
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   */
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184k
  if (!BN_rshift(a, m, recp->num_bits))
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0
    goto err;
167
184k
  if (!BN_mul(b, a, recp->Nr, ctx))
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0
    goto err;
169
184k
  if (!BN_rshift(d, b, i - recp->num_bits))
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0
    goto err;
171
184k
  d->neg = 0;
172
173
184k
  if (!BN_mul(b, recp->N, d, ctx))
174
0
    goto err;
175
184k
  if (!BN_usub(r, m, b))
176
0
    goto err;
177
184k
  r->neg = 0;
178
179
184k
#if 1
180
184k
  j = 0;
181
340k
  while (BN_ucmp(r, recp->N) >= 0) {
182
156k
    if (j++ > 2) {
183
0
      BNerror(BN_R_BAD_RECIPROCAL);
184
0
      goto err;
185
0
    }
186
156k
    if (!BN_usub(r, r, recp->N))
187
0
      goto err;
188
156k
    if (!BN_add_word(d, 1))
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0
      goto err;
190
156k
  }
191
184k
#endif
192
193
184k
  BN_set_negative(r, m->neg);
194
184k
  BN_set_negative(d, m->neg ^ recp->N->neg);
195
196
184k
  ret = 1;
197
198
184k
err:
199
184k
  BN_CTX_end(ctx);
200
184k
  return ret;
201
184k
}
202
203
/* Compute r = (x * y) % m. */
204
int
205
BN_mod_mul_reciprocal(BIGNUM *r, const BIGNUM *x, const BIGNUM *y,
206
    BN_RECP_CTX *recp, BN_CTX *ctx)
207
28.5k
{
208
28.5k
  if (!BN_mul(r, x, y, ctx))
209
0
    return 0;
210
211
28.5k
  return BN_div_reciprocal(NULL, r, r, recp, ctx);
212
28.5k
}
213
214
/* Compute r = x^2 % m. */
215
int
216
BN_mod_sqr_reciprocal(BIGNUM *r, const BIGNUM *x, BN_RECP_CTX *recp, BN_CTX *ctx)
217
168k
{
218
168k
  if (!BN_sqr(r, x, ctx))
219
0
    return 0;
220
221
168k
  return BN_div_reciprocal(NULL, r, r, recp, ctx);
222
168k
}