crypto/bn/bn_gcd.c

   1 /* crypto/bn/bn_gcd.c */
   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 #include "cryptlib.h"
  61 #include "bn_lcl.h"
  62
  63 #ifndef NOPROTO
  64 static BIGNUM *euclid(BIGNUM *a, BIGNUM *b);
  65 #else
  66 static BIGNUM *euclid();
  67 #endif
  68
  69 int BN_gcd(r,in_a,in_b,ctx)
  70 BIGNUM *r,*in_a,*in_b;
  71 BN_CTX *ctx;
  72         {
  73         BIGNUM *a,*b,*t;
  74         int ret=0;
  75
  76         bn_check_top(in_a);
  77         bn_check_top(in_b);
  78
  79         a= &(ctx->bn[ctx->tos]);
  80         b= &(ctx->bn[ctx->tos+1]);
  81
  82         if (BN_copy(a,in_a) == NULL) goto err;
  83         if (BN_copy(b,in_b) == NULL) goto err;
  84
  85         if (BN_cmp(a,b) < 0) { t=a; a=b; b=t; }
  86         t=euclid(a,b);
  87         if (t == NULL) goto err;
  88
  89         if (BN_copy(r,t) == NULL) goto err;
  90         ret=1;
  91 err:
  92         return(ret);
  93         }
  94
  95 static BIGNUM *euclid(a,b)
  96 BIGNUM *a,*b;
  97         {
  98         BIGNUM *t;
  99         int shifts=0;
 100
 101         bn_check_top(a);
 102         bn_check_top(b);
 103
 104         for (;;)
 105                 {
 106                 if (BN_is_zero(b))
 107                         break;
 108
 109                 if (BN_is_odd(a))
 110                         {
 111                         if (BN_is_odd(b))
 112                                 {
 113                                 if (!BN_sub(a,a,b)) goto err;
 114                                 if (!BN_rshift1(a,a)) goto err;
 115                                 if (BN_cmp(a,b) < 0)
 116                                         { t=a; a=b; b=t; }
 117                                 }
 118                         else            /* a odd - b even */
 119                                 {
 120                                 if (!BN_rshift1(b,b)) goto err;
 121                                 if (BN_cmp(a,b) < 0)
 122                                         { t=a; a=b; b=t; }
 123                                 }
 124                         }
 125                 else                    /* a is even */
 126                         {
 127                         if (BN_is_odd(b))
 128                                 {
 129                                 if (!BN_rshift1(a,a)) goto err;
 130                                 if (BN_cmp(a,b) < 0)
 131                                         { t=a; a=b; b=t; }
 132                                 }
 133                         else            /* a even - b even */
 134                                 {
 135                                 if (!BN_rshift1(a,a)) goto err;
 136                                 if (!BN_rshift1(b,b)) goto err;
 137                                 shifts++;
 138                                 }
 139                         }
 140                 }
 141         if (shifts)
 142                 {
 143                 if (!BN_lshift(a,a,shifts)) goto err;
 144                 }
 145         return(a);
 146 err:
 147         return(NULL);
 148         }
 149
 150 /* solves ax == 1 (mod n) */
 151 BIGNUM *BN_mod_inverse(in, a, n, ctx)
 152 BIGNUM *in;
 153 BIGNUM *a;
 154 BIGNUM *n;
 155 BN_CTX *ctx;
 156         {
 157         BIGNUM *A,*B,*X,*Y,*M,*D,*R;
 158         BIGNUM *T,*ret=NULL;
 159         int sign;
 160
 161         bn_check_top(a);
 162         bn_check_top(n);
 163
 164         A= &(ctx->bn[ctx->tos]);
 165         B= &(ctx->bn[ctx->tos+1]);
 166         X= &(ctx->bn[ctx->tos+2]);
 167         D= &(ctx->bn[ctx->tos+3]);
 168         M= &(ctx->bn[ctx->tos+4]);
 169         Y= &(ctx->bn[ctx->tos+5]);
 170         ctx->tos+=6;
 171         if (in == NULL)
 172                 R=BN_new();
 173         else
 174                 R=in;
 175         if (R == NULL) goto err;
 176
 177         BN_zero(X);
 178         BN_one(Y);
 179         if (BN_copy(A,a) == NULL) goto err;
 180         if (BN_copy(B,n) == NULL) goto err;
 181         sign=1;
 182
 183         while (!BN_is_zero(B))
 184                 {
 185                 if (!BN_div(D,M,A,B,ctx)) goto err;
 186                 T=A;
 187                 A=B;
 188                 B=M;
 189                 /* T has a struct, M does not */
 190
 191                 if (!BN_mul(T,D,X,ctx)) goto err;
 192                 if (!BN_add(T,T,Y)) goto err;
 193                 M=Y;
 194                 Y=X;
 195                 X=T;
 196                 sign= -sign;
 197                 }
 198         if (sign < 0)
 199                 {
 200                 if (!BN_sub(Y,n,Y)) goto err;
 201                 }
 202
 203         if (BN_is_one(A))
 204                 { if (!BN_mod(R,Y,n,ctx)) goto err; }
 205         else
 206                 {
 207                 BNerr(BN_F_BN_MOD_INVERSE,BN_R_NO_INVERSE);
 208                 goto err;
 209                 }
 210         ret=R;
 211 err:
 212         if ((ret == NULL) && (in == NULL)) BN_free(R);
 213         ctx->tos-=6;
 214         return(ret);
 215         }
 216