lib/libcrypto/bn/bn_recp.c

   1 /* $OpenBSD: bn_recp.c,v 1.15 2017/01/29 17:49:22 beck Exp $ */
   2 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
   3  * All rights reserved.
   4  *
   5  * This package is an SSL implementation written
   6  * by Eric Young (eay@cryptsoft.com).
   7  * The implementation was written so as to conform with Netscapes SSL.
   8  *
   9  * This library is free for commercial and non-commercial use as long as
  10  * the following conditions are aheared to.  The following conditions
  11  * apply to all code found in this distribution, be it the RC4, RSA,
  12  * lhash, DES, etc., code; not just the SSL code.  The SSL documentation
  13  * included with this distribution is covered by the same copyright terms
  14  * except that the holder is Tim Hudson (tjh@cryptsoft.com).
  15  *
  16  * Copyright remains Eric Young's, and as such any Copyright notices in
  17  * the code are not to be removed.
  18  * If this package is used in a product, Eric Young should be given attribution
  19  * as the author of the parts of the library used.
  20  * This can be in the form of a textual message at program startup or
  21  * in documentation (online or textual) provided with the package.
  22  *
  23  * Redistribution and use in source and binary forms, with or without
  24  * modification, are permitted provided that the following conditions
  25  * are met:
  26  * 1. Redistributions of source code must retain the copyright
  27  *    notice, this list of conditions and the following disclaimer.
  28  * 2. Redistributions in binary form must reproduce the above copyright
  29  *    notice, this list of conditions and the following disclaimer in the
  30  *    documentation and/or other materials provided with the distribution.
  31  * 3. All advertising materials mentioning features or use of this software
  32  *    must display the following acknowledgement:
  33  *    "This product includes cryptographic software written by
  34  *     Eric Young (eay@cryptsoft.com)"
  35  *    The word 'cryptographic' can be left out if the rouines from the library
  36  *    being used are not cryptographic related :-).
  37  * 4. If you include any Windows specific code (or a derivative thereof) from
  38  *    the apps directory (application code) you must include an acknowledgement:
  39  *    "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
  40  *
  41  * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
  42  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  43  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  44  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  45  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  46  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  47  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  48  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  49  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  50  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  51  * SUCH DAMAGE.
  52  *
  53  * The licence and distribution terms for any publically available version or
  54  * derivative of this code cannot be changed.  i.e. this code cannot simply be
  55  * copied and put under another distribution licence
  56  * [including the GNU Public Licence.]
  57  */
  58
  59 #include <stdio.h>
  60
  61 #include <openssl/err.h>
  62
  63 #include "bn_lcl.h"
  64
  65 void
  66 BN_RECP_CTX_init(BN_RECP_CTX *recp)
  67 {
  68         BN_init(&(recp->N));
  69         BN_init(&(recp->Nr));
  70         recp->num_bits = 0;
  71         recp->flags = 0;
  72 }
  73
  74 BN_RECP_CTX *
  75 BN_RECP_CTX_new(void)
  76 {
  77         BN_RECP_CTX *ret;
  78
  79         if ((ret = malloc(sizeof(BN_RECP_CTX))) == NULL)
  80                 return (NULL);
  81
  82         BN_RECP_CTX_init(ret);
  83         ret->flags = BN_FLG_MALLOCED;
  84         return (ret);
  85 }
  86
  87 void
  88 BN_RECP_CTX_free(BN_RECP_CTX *recp)
  89 {
  90         if (recp == NULL)
  91                 return;
  92
  93         BN_free(&(recp->N));
  94         BN_free(&(recp->Nr));
  95         if (recp->flags & BN_FLG_MALLOCED)
  96                 free(recp);
  97 }
  98
  99 int
 100 BN_RECP_CTX_set(BN_RECP_CTX *recp, const BIGNUM *d, BN_CTX *ctx)
 101 {
 102         if (!BN_copy(&(recp->N), d))
 103                 return 0;
 104         BN_zero(&(recp->Nr));
 105         recp->num_bits = BN_num_bits(d);
 106         recp->shift = 0;
 107         return (1);
 108 }
 109
 110 int
 111 BN_mod_mul_reciprocal(BIGNUM *r, const BIGNUM *x, const BIGNUM *y,
 112     BN_RECP_CTX *recp, BN_CTX *ctx)
 113 {
 114         int ret = 0;
 115         BIGNUM *a;
 116         const BIGNUM *ca;
 117
 118         BN_CTX_start(ctx);
 119         if ((a = BN_CTX_get(ctx)) == NULL)
 120                 goto err;
 121         if (y != NULL) {
 122                 if (x == y) {
 123                         if (!BN_sqr(a, x, ctx))
 124                                 goto err;
 125                 } else {
 126                         if (!BN_mul(a, x, y, ctx))
 127                                 goto err;
 128                 }
 129                 ca = a;
 130         } else
 131                 ca = x; /* Just do the mod */
 132
 133         ret = BN_div_recp(NULL, r, ca, recp, ctx);
 134
 135 err:
 136         BN_CTX_end(ctx);
 137         bn_check_top(r);
 138         return (ret);
 139 }
 140
 141 int
 142 BN_div_recp(BIGNUM *dv, BIGNUM *rem, const BIGNUM *m, BN_RECP_CTX *recp,
 143     BN_CTX *ctx)
 144 {
 145         int i, j, ret = 0;
 146         BIGNUM *a, *b, *d, *r;
 147
 148         BN_CTX_start(ctx);
 149         a = BN_CTX_get(ctx);
 150         b = BN_CTX_get(ctx);
 151         if (dv != NULL)
 152                 d = dv;
 153         else
 154                 d = BN_CTX_get(ctx);
 155         if (rem != NULL)
 156                 r = rem;
 157         else
 158                 r = BN_CTX_get(ctx);
 159         if (a == NULL || b == NULL || d == NULL || r == NULL)
 160                 goto err;
 161
 162         if (BN_ucmp(m, &(recp->N)) < 0) {
 163                 BN_zero(d);
 164                 if (!BN_copy(r, m)) {
 165                         BN_CTX_end(ctx);
 166                         return 0;
 167                 }
 168                 BN_CTX_end(ctx);
 169                 return (1);
 170         }
 171
 172         /* We want the remainder
 173          * Given input of ABCDEF / ab
 174          * we need multiply ABCDEF by 3 digests of the reciprocal of ab
 175          *
 176          */
 177
 178         /* i := max(BN_num_bits(m), 2*BN_num_bits(N)) */
 179         i = BN_num_bits(m);
 180         j = recp->num_bits << 1;
 181         if (j > i)
 182                 i = j;
 183
 184         /* Nr := round(2^i / N) */
 185         if (i != recp->shift)
 186                 recp->shift = BN_reciprocal(&(recp->Nr), &(recp->N), i, ctx);
 187
 188         /* BN_reciprocal returns i, or -1 for an error */
 189         if (recp->shift == -1)
 190                 goto err;
 191
 192         /* d := |round(round(m / 2^BN_num_bits(N)) * recp->Nr / 2^(i - BN_num_bits(N)))|
 193          *    = |round(round(m / 2^BN_num_bits(N)) * round(2^i / N) / 2^(i - BN_num_bits(N)))|
 194          *   <= |(m / 2^BN_num_bits(N)) * (2^i / N) * (2^BN_num_bits(N) / 2^i)|
 195          *    = |m/N|
 196          */
 197         if (!BN_rshift(a, m, recp->num_bits))
 198                 goto err;
 199         if (!BN_mul(b, a,&(recp->Nr), ctx))
 200                 goto err;
 201         if (!BN_rshift(d, b, i - recp->num_bits))
 202                 goto err;
 203         d->neg = 0;
 204
 205         if (!BN_mul(b, &(recp->N), d, ctx))
 206                 goto err;
 207         if (!BN_usub(r, m, b))
 208                 goto err;
 209         r->neg = 0;
 210
 211 #if 1
 212         j = 0;
 213         while (BN_ucmp(r, &(recp->N)) >= 0) {
 214                 if (j++ > 2) {
 215                         BNerror(BN_R_BAD_RECIPROCAL);
 216                         goto err;
 217                 }
 218                 if (!BN_usub(r, r, &(recp->N)))
 219                         goto err;
 220                 if (!BN_add_word(d, 1))
 221                         goto err;
 222         }
 223 #endif
 224
 225         r->neg = BN_is_zero(r) ? 0 : m->neg;
 226         d->neg = m->neg^recp->N.neg;
 227         ret = 1;
 228
 229 err:
 230         BN_CTX_end(ctx);
 231         bn_check_top(dv);
 232         bn_check_top(rem);
 233         return (ret);
 234 }
 235
 236 /* len is the expected size of the result
 237  * We actually calculate with an extra word of precision, so
 238  * we can do faster division if the remainder is not required.
 239  */
 240 /* r := 2^len / m */
 241 int
 242 BN_reciprocal(BIGNUM *r, const BIGNUM *m, int len, BN_CTX *ctx)
 243 {
 244         int ret = -1;
 245         BIGNUM *t;
 246
 247         BN_CTX_start(ctx);
 248         if ((t = BN_CTX_get(ctx)) == NULL)
 249                 goto err;
 250
 251         if (!BN_set_bit(t, len))
 252                 goto err;
 253
 254         if (!BN_div_ct(r, NULL, t,m, ctx))
 255                 goto err;
 256
 257         ret = len;
 258
 259 err:
 260         bn_check_top(r);
 261         BN_CTX_end(ctx);
 262         return (ret);
 263 }