crypto/bn/bn_recp.c

   1 /* crypto/bn/bn_recp.c */
   2 /* Copyright (C) 1995-1997 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 #include "cryptlib.h"
  61 #include "bn_lcl.h"
  62
  63 int BN_mod_mul_reciprocal(r, x, y, m, i, nb, ctx)
  64 BIGNUM *r;
  65 BIGNUM *x;
  66 BIGNUM *y;
  67 BIGNUM *m;
  68 BIGNUM *i;
  69 int nb;
  70 BN_CTX *ctx;
  71         {
  72         int ret=0,j;
  73         BIGNUM *a,*b,*c,*d;
  74
  75         a=ctx->bn[ctx->tos++];
  76         b=ctx->bn[ctx->tos++];
  77         c=ctx->bn[ctx->tos++];
  78         d=ctx->bn[ctx->tos++];
  79
  80         if (x == y)
  81                 { if (!BN_sqr(a,x,ctx)) goto err; }
  82         else
  83                 { if (!BN_mul(a,x,y)) goto err; }
  84         if (!BN_rshift(d,a,nb)) goto err;
  85         if (!BN_mul(b,d,i)) goto err;
  86         if (!BN_rshift(c,b,nb)) goto err;
  87         if (!BN_mul(b,m,c)) goto err;
  88         if (!BN_sub(r,a,b)) goto err;
  89         j=0;
  90         while (BN_cmp(r,m) >= 0)
  91                 {
  92                 if (j++ > 2)
  93                         {
  94                         BNerr(BN_F_BN_MOD_MUL_RECIPROCAL,BN_R_BAD_RECIPROCAL);
  95                         goto err;
  96                         }
  97                 if (!BN_sub(r,r,m)) goto err;
  98                 }
  99
 100         ret=1;
 101 err:
 102         ctx->tos-=4;
 103         return(ret);
 104         }
 105
 106 int BN_reciprocal(r, m,ctx)
 107 BIGNUM *r;
 108 BIGNUM *m;
 109 BN_CTX *ctx;
 110         {
 111         int nm,ret= -1;
 112         BIGNUM *t;
 113
 114         t=ctx->bn[ctx->tos++];
 115
 116         nm=BN_num_bits(m);
 117         if (!BN_lshift(t,BN_value_one(),nm*2)) goto err;
 118
 119         if (!BN_div(r,NULL,t,m,ctx)) goto err;
 120         ret=nm;
 121 err:
 122         ctx->tos--;
 123         return(ret);
 124         }
 125