1  /* crypto/bn/bn_exp.c */


2  /* Copyright (C) 19951998 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 noncommercial 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  * Copyright (c) 19982000 The OpenSSL Project. All rights reserved.


60  *


61  * Redistribution and use in source and binary forms, with or without


62  * modification, are permitted provided that the following conditions


63  * are met:


64  *


65  * 1. Redistributions of source code must retain the above copyright


66  * notice, this list of conditions and the following disclaimer.


67  *


68  * 2. Redistributions in binary form must reproduce the above copyright


69  * notice, this list of conditions and the following disclaimer in


70  * the documentation and/or other materials provided with the


71  * distribution.


72  *


73  * 3. All advertising materials mentioning features or use of this


74  * software must display the following acknowledgment:


75  * "This product includes software developed by the OpenSSL Project


76  * for use in the OpenSSL Toolkit. (http://www.openssl.org/)"


77  *


78  * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to


79  * endorse or promote products derived from this software without


80  * prior written permission. For written permission, please contact


81  * opensslcore@openssl.org.


82  *


83  * 5. Products derived from this software may not be called "OpenSSL"


84  * nor may "OpenSSL" appear in their names without prior written


85  * permission of the OpenSSL Project.


86  *


87  * 6. Redistributions of any form whatsoever must retain the following


88  * acknowledgment:


89  * "This product includes software developed by the OpenSSL Project


90  * for use in the OpenSSL Toolkit (http://www.openssl.org/)"


91  *


92  * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY


93  * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE


94  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR


95  * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE OpenSSL PROJECT OR


96  * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,


97  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT


98  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;


99  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)


100  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,


101  * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)


102  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED


103  * OF THE POSSIBILITY OF SUCH DAMAGE.


104  * ====================================================================


105  *


106  * This product includes cryptographic software written by Eric Young


107  * (eay@cryptsoft.com). This product includes software written by Tim


108  * Hudson (tjh@cryptsoft.com).


109  *


110  */


111 


112 


113  #include <stdio.h>


114  #include "bn_lcl.h"


115 


116  #define TABLE_SIZE 32


117 


118  /* slow but works */


119  int BN_mod_mul(BIGNUM *ret, BIGNUM *a, BIGNUM *b, const BIGNUM *m, BN_CTX *ctx)


120  {


121  BIGNUM *t;


122  int r=0;


123 


124  bn_check_top(a);


125  bn_check_top(b);


126  bn_check_top(m);


127 


128  BN_CTX_start(ctx);


129  if ((t = BN_CTX_get(ctx)) == NULL) goto err;


130  if (a == b)


131  { if (!BN_sqr(t,a,ctx)) goto err; }


132  else


133  { if (!BN_mul(t,a,b,ctx)) goto err; }


134  if (!BN_mod(ret,t,m,ctx)) goto err;


135  r=1;


136  err:


137  BN_CTX_end(ctx);


138  return(r);


139  }


140 


141 


142  int BN_mod_exp(BIGNUM *r, BIGNUM *a, const BIGNUM *p, const BIGNUM *m,


143  BN_CTX *ctx)


144  {


145  int ret;


146 


147  bn_check_top(a);


148  bn_check_top(p);


149  bn_check_top(m);


150 


151  ret=BN_mod_exp_simple(r,a,p,m,ctx);


152 


153  return(ret);


154  }


155 


156 


157 


158 


159 


160  /* The old fallback, simple version :) */


161  int BN_mod_exp_simple(BIGNUM *r, BIGNUM *a, const BIGNUM *p, const BIGNUM *m,


162  BN_CTX *ctx)


163  {


164  int i,j,bits,ret=0,wstart,wend,window,wvalue,ts=0;


165  int start=1;


166  BIGNUM *d;


167  BIGNUM val[TABLE_SIZE];


168 


169  bits=BN_num_bits(p);


170 


171  if (bits == 0)


172  {


173  BN_one(r);


174  return(1);


175  }


176 


177  BN_CTX_start(ctx);


178  if ((d = BN_CTX_get(ctx)) == NULL) goto err;


179 


180  BN_init(&(val[0]));


181  ts=1;


182  if (!BN_mod(&(val[0]),a,m,ctx)) goto err; /* 1 */


183 


184  window = BN_window_bits_for_exponent_size(bits);


185  if (window > 1)


186  {


187  if (!BN_mod_mul(d,&(val[0]),&(val[0]),m,ctx))


188  goto err; /* 2 */


189  j=1<<(window1);


190  for (i=1; i<j; i++)


191  {


192  BN_init(&(val[i]));


193  if (!BN_mod_mul(&(val[i]),&(val[i1]),d,m,ctx))


194  goto err;


195  }


196  ts=i;


197  }


198 


199  start=1; /* This is used to avoid multiplication etc


200  * when there is only the value '1' in the


201  * buffer. */


202  wvalue=0; /* The 'value' of the window */


203  wstart=bits1; /* The top bit of the window */


204  wend=0; /* The bottom bit of the window */


205 


206  if (!BN_one(r)) goto err;


207 


208  for (;;)


209  {


210  if (BN_is_bit_set(p,wstart) == 0)


211  {


212  if (!start)


213  if (!BN_mod_mul(r,r,r,m,ctx))


214  goto err;


215  if (wstart == 0) break;


216  wstart;


217  continue;


218  }


219  /* We now have wstart on a 'set' bit, we now need to work out


220  * how bit a window to do. To do this we need to scan


221  * forward until the last set bit before the end of the


222  * window */


223  j=wstart;


224  wvalue=1;


225  wend=0;


226  for (i=1; i<window; i++)


227  {


228  if (wstarti < 0) break;


229  if (BN_is_bit_set(p,wstarti))


230  {


231  wvalue<<=(iwend);


232  wvalue=1;


233  wend=i;


234  }


235  }


236 


237  /* wend is the size of the current window */


238  j=wend+1;


239  /* add the 'bytes above' */


240  if (!start)


241  for (i=0; i<j; i++)


242  {


243  if (!BN_mod_mul(r,r,r,m,ctx))


244  goto err;


245  }


246 


247  /* wvalue will be an odd number < 2^window */


248  if (!BN_mod_mul(r,r,&(val[wvalue>>1]),m,ctx))


249  goto err;


250 


251  /* move the 'window' down further */


252  wstart=wend+1;


253  wvalue=0;


254  start=0;


255  if (wstart < 0) break;


256  }


257  ret=1;


258  err:


259  BN_CTX_end(ctx);


260  for (i=0; i<ts; i++)


261  BN_clear_free(&(val[i]));


262  return(ret);


263  }


264 

