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