crypto/bn/bn_gcd.c

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