OSX/libsecurity_apple_csp/open_ssl/bn/bn_exp.c

   1 /* crypto/bn/bn_exp.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  * Copyright (c) 1998-2000 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  *    openssl-core@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 "cryptlib.h"
 115 #include "bn_lcl.h"
 116 #ifdef ATALLA
 117 # include <alloca.h>
 118 # include <atasi.h>
 119 # include <assert.h>
 120 # include <dlfcn.h>
 121 #endif
 122
 123
 124 #define TABLE_SIZE      32
 125
 126 /* slow but works */
 127 int BN_mod_mul(BIGNUM *ret, BIGNUM *a, BIGNUM *b, const BIGNUM *m, BN_CTX *ctx)
 128         {
 129         BIGNUM *t;
 130         int r=0;
 131
 132         bn_check_top(a);
 133         bn_check_top(b);
 134         bn_check_top(m);
 135
 136         BN_CTX_start(ctx);
 137         if ((t = BN_CTX_get(ctx)) == NULL) goto err;
 138         if (a == b)
 139                 { if (!BN_sqr(t,a,ctx)) goto err; }
 140         else
 141                 { if (!BN_mul(t,a,b,ctx)) goto err; }
 142         if (!BN_mod(ret,t,m,ctx)) goto err;
 143         r=1;
 144 err:
 145         BN_CTX_end(ctx);
 146         return(r);
 147         }
 148
 149
 150 /* this one works - simple but works */
 151 int BN_exp(BIGNUM *r, BIGNUM *a, BIGNUM *p, BN_CTX *ctx)
 152         {
 153         int i,bits,ret=0;
 154         BIGNUM *v,*rr;
 155
 156         BN_CTX_start(ctx);
 157         if ((r == a) || (r == p))
 158                 rr = BN_CTX_get(ctx);
 159         else
 160                 rr = r;
 161         if ((v = BN_CTX_get(ctx)) == NULL) goto err;
 162
 163         if (BN_copy(v,a) == NULL) goto err;
 164         bits=BN_num_bits(p);
 165
 166         if (BN_is_odd(p))
 167                 { if (BN_copy(rr,a) == NULL) goto err; }
 168         else    { if (!BN_one(rr)) goto err; }
 169
 170         for (i=1; i<bits; i++)
 171                 {
 172                 if (!BN_sqr(v,v,ctx)) goto err;
 173                 if (BN_is_bit_set(p,i))
 174                         {
 175                         if (!BN_mul(rr,rr,v,ctx)) goto err;
 176                         }
 177                 }
 178         ret=1;
 179 err:
 180         if (r != rr) BN_copy(r,rr);
 181         BN_CTX_end(ctx);
 182         return(ret);
 183         }
 184
 185
 186 #ifdef ATALLA
 187
 188 /*
 189  * This routine will dynamically check for the existance of an Atalla AXL-200
 190  * SSL accelerator module.  If one is found, the variable
 191  * asi_accelerator_present is set to 1 and the function pointers
 192  * ptr_ASI_xxxxxx above will be initialized to corresponding ASI API calls.
 193  */
 194 typedef int tfnASI_GetPerformanceStatistics(int reset_flag,
 195                                             unsigned int *ret_buf);
 196 typedef int tfnASI_GetHardwareConfig(long card_num, unsigned int *ret_buf);
 197 typedef int tfnASI_RSAPrivateKeyOpFn(RSAPrivateKey * rsaKey,
 198                                      unsigned char *output,
 199                                      unsigned char *input,
 200                                      unsigned int modulus_len);
 201
 202 static tfnASI_GetHardwareConfig *ptr_ASI_GetHardwareConfig;
 203 static tfnASI_RSAPrivateKeyOpFn *ptr_ASI_RSAPrivateKeyOpFn;
 204 static tfnASI_GetPerformanceStatistics *ptr_ASI_GetPerformanceStatistics;
 205 static int asi_accelerator_present;
 206 static int tried_atalla;
 207
 208 void atalla_initialize_accelerator_handle(void)
 209         {
 210         void *dl_handle;
 211         int status;
 212         unsigned int config_buf[1024];
 213         static int tested;
 214
 215         if(tested)
 216                 return;
 217
 218         tested=1;
 219
 220         bzero((void *)config_buf, 1024);
 221
 222         /*
 223          * Check to see if the library is present on the system
 224          */
 225         dl_handle = dlopen("atasi.so", RTLD_NOW);
 226         if (dl_handle == (void *) NULL)
 227                 {
 228 /*              printf("atasi.so library is not present on the system\n");
 229                 printf("No HW acceleration available\n");*/
 230                 return;
 231                 }
 232
 233         /*
 234          * The library is present.  Now we'll check to insure that the
 235          * LDM is up and running. First we'll get the address of the
 236          * function in the atasi library that we need to see if the
 237          * LDM is operating.
 238          */
 239
 240         ptr_ASI_GetHardwareConfig =
 241           (tfnASI_GetHardwareConfig *)dlsym(dl_handle,"ASI_GetHardwareConfig");
 242
 243         if (ptr_ASI_GetHardwareConfig)
 244                 {
 245                 /*
 246                  * We found the call, now we'll get our config
 247                  * status.  If we get a non 0 result, the LDM is not
 248                  * running and we cannot use the Atalla ASI *
 249                  * library.
 250                  */
 251                 status = (*ptr_ASI_GetHardwareConfig)(0L, config_buf);
 252                 if (status != 0)
 253                         {
 254                         printf("atasi.so library is present but not initialized\n");
 255                         printf("No HW acceleration available\n");
 256                         return;
 257                         }
 258                 }
 259         else
 260                 {
 261 /*              printf("We found the library, but not the function. Very Strange!\n");*/
 262                 return ;
 263                 }
 264
 265         /*
 266          * It looks like we have acceleration capabilities.  Load up the
 267          * pointers to our ASI API calls.
 268          */
 269         ptr_ASI_RSAPrivateKeyOpFn=
 270           (tfnASI_RSAPrivateKeyOpFn *)dlsym(dl_handle, "ASI_RSAPrivateKeyOpFn");
 271         if (ptr_ASI_RSAPrivateKeyOpFn == NULL)
 272                 {
 273 /*              printf("We found the library, but no RSA function. Very Strange!\n");*/
 274                 return;
 275                 }
 276
 277         ptr_ASI_GetPerformanceStatistics =
 278           (tfnASI_GetPerformanceStatistics *)dlsym(dl_handle, "ASI_GetPerformanceStatistics");
 279         if (ptr_ASI_GetPerformanceStatistics == NULL)
 280                 {
 281 /*              printf("We found the library, but no stat function. Very Strange!\n");*/
 282                 return;
 283               }
 284
 285         /*
 286          * Indicate that acceleration is available
 287          */
 288         asi_accelerator_present = 1;
 289
 290 /*      printf("This system has acceleration!\n");*/
 291
 292         return;
 293         }
 294
 295 /* make sure this only gets called once when bn_mod_exp calls bn_mod_exp_mont */
 296 int BN_mod_exp_atalla(BIGNUM *r, BIGNUM *a, const BIGNUM *p, const BIGNUM *m)
 297         {
 298         unsigned char *abin;
 299         unsigned char *pbin;
 300         unsigned char *mbin;
 301         unsigned char *rbin;
 302         int an,pn,mn,ret;
 303         RSAPrivateKey keydata;
 304
 305         atalla_initialize_accelerator_handle();
 306         if(!asi_accelerator_present)
 307                 return 0;
 308
 309
 310 /* We should be able to run without size testing */
 311 # define ASIZE  128
 312         an=BN_num_bytes(a);
 313         pn=BN_num_bytes(p);
 314         mn=BN_num_bytes(m);
 315
 316         if(an <= ASIZE && pn <= ASIZE && mn <= ASIZE)
 317             {
 318             int size=mn;
 319
 320             assert(an <= mn);
 321             abin=alloca(size);
 322             memset(abin,'\0',mn);
 323             BN_bn2bin(a,abin+size-an);
 324
 325             pbin=alloca(pn);
 326             BN_bn2bin(p,pbin);
 327
 328             mbin=alloca(size);
 329             memset(mbin,'\0',mn);
 330             BN_bn2bin(m,mbin+size-mn);
 331
 332             rbin=alloca(size);
 333
 334             memset(&keydata,'\0',sizeof keydata);
 335             keydata.privateExponent.data=pbin;
 336             keydata.privateExponent.len=pn;
 337             keydata.modulus.data=mbin;
 338             keydata.modulus.len=size;
 339
 340             ret=(*ptr_ASI_RSAPrivateKeyOpFn)(&keydata,rbin,abin,keydata.modulus.len);
 341 /*fprintf(stderr,"!%s\n",BN_bn2hex(a));*/
 342             if(!ret)
 343                 {
 344                 BN_bin2bn(rbin,keydata.modulus.len,r);
 345 /*fprintf(stderr,"?%s\n",BN_bn2hex(r));*/
 346                 return 1;
 347                 }
 348             }
 349         return 0;
 350         }
 351 #endif /* def ATALLA */
 352
 353
 354 int BN_mod_exp(BIGNUM *r, BIGNUM *a, const BIGNUM *p, const BIGNUM *m,
 355                BN_CTX *ctx)
 356         {
 357         int ret;
 358
 359         bn_check_top(a);
 360         bn_check_top(p);
 361         bn_check_top(m);
 362
 363 #ifdef ATALLA
 364         if(BN_mod_exp_atalla(r,a,p,m))
 365             return 1;
 366 /* If it fails, try the other methods (but don't try atalla again) */
 367         tried_atalla=1;
 368 #endif
 369
 370 #ifdef MONT_MUL_MOD
 371         /* I have finally been able to take out this pre-condition of
 372          * the top bit being set.  It was caused by an error in BN_div
 373          * with negatives.  There was also another problem when for a^b%m
 374          * a >= m.  eay 07-May-97 */
 375 /*      if ((m->d[m->top-1]&BN_TBIT) && BN_is_odd(m)) */
 376
 377         if (BN_is_odd(m))
 378                 {
 379                 if (a->top == 1)
 380                         {
 381                         BN_ULONG A = a->d[0];
 382                         ret=BN_mod_exp_mont_word(r,A,p,m,ctx,NULL);
 383                         }
 384                 else
 385                         ret=BN_mod_exp_mont(r,a,p,m,ctx,NULL);
 386                 }
 387         else
 388 #endif
 389 #ifdef RECP_MUL_MOD
 390                 { ret=BN_mod_exp_recp(r,a,p,m,ctx); }
 391 #else
 392                 { ret=BN_mod_exp_simple(r,a,p,m,ctx); }
 393 #endif
 394
 395 #ifdef ATALLA
 396         tried_atalla=0;
 397 #endif
 398
 399         return(ret);
 400         }
 401
 402
 403 int BN_mod_exp_recp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p,
 404                     const BIGNUM *m, BN_CTX *ctx)
 405         {
 406         int i,j,bits,ret=0,wstart,wend,window,wvalue;
 407         int start=1,ts=0;
 408         BIGNUM *aa;
 409         BIGNUM val[TABLE_SIZE];
 410         BN_RECP_CTX recp;
 411
 412         bits=BN_num_bits(p);
 413
 414         if (bits == 0)
 415                 {
 416                 BN_one(r);
 417                 return(1);
 418                 }
 419
 420         BN_CTX_start(ctx);
 421         if ((aa = BN_CTX_get(ctx)) == NULL) goto err;
 422
 423         BN_RECP_CTX_init(&recp);
 424         if (BN_RECP_CTX_set(&recp,m,ctx) <= 0) goto err;
 425
 426         BN_init(&(val[0]));
 427         ts=1;
 428
 429         if (!BN_mod(&(val[0]),a,m,ctx)) goto err;               /* 1 */
 430
 431         window = BN_window_bits_for_exponent_size(bits);
 432         if (window > 1)
 433                 {
 434                 if (!BN_mod_mul_reciprocal(aa,&(val[0]),&(val[0]),&recp,ctx))
 435                         goto err;                               /* 2 */
 436                 j=1<<(window-1);
 437                 for (i=1; i<j; i++)
 438                         {
 439                         BN_init(&val[i]);
 440                         if (!BN_mod_mul_reciprocal(&(val[i]),&(val[i-1]),aa,&recp,ctx))
 441                                 goto err;
 442                         }
 443                 ts=i;
 444                 }
 445
 446         start=1;        /* This is used to avoid multiplication etc
 447                          * when there is only the value '1' in the
 448                          * buffer. */
 449         wvalue=0;       /* The 'value' of the window */
 450         wstart=bits-1;  /* The top bit of the window */
 451         wend=0;         /* The bottom bit of the window */
 452
 453         if (!BN_one(r)) goto err;
 454
 455         for (;;)
 456                 {
 457                 if (BN_is_bit_set(p,wstart) == 0)
 458                         {
 459                         if (!start)
 460                                 if (!BN_mod_mul_reciprocal(r,r,r,&recp,ctx))
 461                                 goto err;
 462                         if (wstart == 0) break;
 463                         wstart--;
 464                         continue;
 465                         }
 466                 /* We now have wstart on a 'set' bit, we now need to work out
 467                  * how bit a window to do.  To do this we need to scan
 468                  * forward until the last set bit before the end of the
 469                  * window */
 470                 j=wstart;
 471                 wvalue=1;
 472                 wend=0;
 473                 for (i=1; i<window; i++)
 474                         {
 475                         if (wstart-i < 0) break;
 476                         if (BN_is_bit_set(p,wstart-i))
 477                                 {
 478                                 wvalue<<=(i-wend);
 479                                 wvalue|=1;
 480                                 wend=i;
 481                                 }
 482                         }
 483
 484                 /* wend is the size of the current window */
 485                 j=wend+1;
 486                 /* add the 'bytes above' */
 487                 if (!start)
 488                         for (i=0; i<j; i++)
 489                                 {
 490                                 if (!BN_mod_mul_reciprocal(r,r,r,&recp,ctx))
 491                                         goto err;
 492                                 }
 493
 494                 /* wvalue will be an odd number < 2^window */
 495                 if (!BN_mod_mul_reciprocal(r,r,&(val[wvalue>>1]),&recp,ctx))
 496                         goto err;
 497
 498                 /* move the 'window' down further */
 499                 wstart-=wend+1;
 500                 wvalue=0;
 501                 start=0;
 502                 if (wstart < 0) break;
 503                 }
 504         ret=1;
 505 err:
 506         BN_CTX_end(ctx);
 507         for (i=0; i<ts; i++)
 508                 BN_clear_free(&(val[i]));
 509         BN_RECP_CTX_free(&recp);
 510         return(ret);
 511         }
 512
 513
 514 int BN_mod_exp_mont(BIGNUM *rr, BIGNUM *a, const BIGNUM *p,
 515                     const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *in_mont)
 516         {
 517         int i,j,bits,ret=0,wstart,wend,window,wvalue;
 518         int start=1,ts=0;
 519         BIGNUM *d,*r;
 520         BIGNUM *aa;
 521         BIGNUM val[TABLE_SIZE];
 522         BN_MONT_CTX *mont=NULL;
 523
 524         bn_check_top(a);
 525         bn_check_top(p);
 526         bn_check_top(m);
 527
 528 #ifdef ATALLA
 529         if(!tried_atalla && BN_mod_exp_atalla(rr,a,p,m))
 530             return 1;
 531 /* If it fails, try the other methods */
 532 #endif
 533
 534         if (!(m->d[0] & 1))
 535                 {
 536                 BNerr(BN_F_BN_MOD_EXP_MONT,BN_R_CALLED_WITH_EVEN_MODULUS);
 537                 return(0);
 538                 }
 539         bits=BN_num_bits(p);
 540         if (bits == 0)
 541                 {
 542                 BN_one(rr);
 543                 return(1);
 544                 }
 545         BN_CTX_start(ctx);
 546         d = BN_CTX_get(ctx);
 547         r = BN_CTX_get(ctx);
 548         if (d == NULL || r == NULL) goto err;
 549
 550         /* If this is not done, things will break in the montgomery
 551          * part */
 552
 553         if (in_mont != NULL)
 554                 mont=in_mont;
 555         else
 556                 {
 557                 if ((mont=BN_MONT_CTX_new()) == NULL) goto err;
 558                 if (!BN_MONT_CTX_set(mont,m,ctx)) goto err;
 559                 }
 560
 561         BN_init(&val[0]);
 562         ts=1;
 563         if (BN_ucmp(a,m) >= 0)
 564                 {
 565                 if (!BN_mod(&(val[0]),a,m,ctx))
 566                         goto err;
 567                 aa= &(val[0]);
 568                 }
 569         else
 570                 aa=a;
 571         if (!BN_to_montgomery(&(val[0]),aa,mont,ctx)) goto err; /* 1 */
 572
 573         window = BN_window_bits_for_exponent_size(bits);
 574         if (window > 1)
 575                 {
 576                 if (!BN_mod_mul_montgomery(d,&(val[0]),&(val[0]),mont,ctx)) goto err; /* 2 */
 577                 j=1<<(window-1);
 578                 for (i=1; i<j; i++)
 579                         {
 580                         BN_init(&(val[i]));
 581                         if (!BN_mod_mul_montgomery(&(val[i]),&(val[i-1]),d,mont,ctx))
 582                                 goto err;
 583                         }
 584                 ts=i;
 585                 }
 586
 587         start=1;        /* This is used to avoid multiplication etc
 588                          * when there is only the value '1' in the
 589                          * buffer. */
 590         wvalue=0;       /* The 'value' of the window */
 591         wstart=bits-1;  /* The top bit of the window */
 592         wend=0;         /* The bottom bit of the window */
 593
 594         if (!BN_to_montgomery(r,BN_value_one(),mont,ctx)) goto err;
 595         for (;;)
 596                 {
 597                 if (BN_is_bit_set(p,wstart) == 0)
 598                         {
 599                         if (!start)
 600                                 {
 601                                 if (!BN_mod_mul_montgomery(r,r,r,mont,ctx))
 602                                 goto err;
 603                                 }
 604                         if (wstart == 0) break;
 605                         wstart--;
 606                         continue;
 607                         }
 608                 /* We now have wstart on a 'set' bit, we now need to work out
 609                  * how bit a window to do.  To do this we need to scan
 610                  * forward until the last set bit before the end of the
 611                  * window */
 612                 j=wstart;
 613                 wvalue=1;
 614                 wend=0;
 615                 for (i=1; i<window; i++)
 616                         {
 617                         if (wstart-i < 0) break;
 618                         if (BN_is_bit_set(p,wstart-i))
 619                                 {
 620                                 wvalue<<=(i-wend);
 621                                 wvalue|=1;
 622                                 wend=i;
 623                                 }
 624                         }
 625
 626                 /* wend is the size of the current window */
 627                 j=wend+1;
 628                 /* add the 'bytes above' */
 629                 if (!start)
 630                         for (i=0; i<j; i++)
 631                                 {
 632                                 if (!BN_mod_mul_montgomery(r,r,r,mont,ctx))
 633                                         goto err;
 634                                 }
 635
 636                 /* wvalue will be an odd number < 2^window */
 637                 if (!BN_mod_mul_montgomery(r,r,&(val[wvalue>>1]),mont,ctx))
 638                         goto err;
 639
 640                 /* move the 'window' down further */
 641                 wstart-=wend+1;
 642                 wvalue=0;
 643                 start=0;
 644                 if (wstart < 0) break;
 645                 }
 646         if (!BN_from_montgomery(rr,r,mont,ctx)) goto err;
 647         ret=1;
 648 err:
 649         if ((in_mont == NULL) && (mont != NULL)) BN_MONT_CTX_free(mont);
 650         BN_CTX_end(ctx);
 651         for (i=0; i<ts; i++)
 652                 BN_clear_free(&(val[i]));
 653         return(ret);
 654         }
 655
 656 int BN_mod_exp_mont_word(BIGNUM *rr, BN_ULONG a, const BIGNUM *p,
 657                          const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *in_mont)
 658         {
 659         BN_MONT_CTX *mont = NULL;
 660         int b, bits, ret=0;
 661         int r_is_one;
 662         BN_ULONG w, next_w;
 663         BIGNUM *d, *r, *t;
 664         BIGNUM *swap_tmp;
 665 #define BN_MOD_MUL_WORD(r, w, m) \
 666                 (BN_mul_word(r, (w)) && \
 667                 (/* BN_ucmp(r, (m)) < 0 ? 1 :*/  \
 668                         (BN_mod(t, r, m, ctx) && (swap_tmp = r, r = t, t = swap_tmp, 1))))
 669                 /* BN_MOD_MUL_WORD is only used with 'w' large,
 670                   * so the BN_ucmp test is probably more overhead
 671                   * than always using BN_mod (which uses BN_copy if
 672                   * a similar test returns true). */
 673 #define BN_TO_MONTGOMERY_WORD(r, w, mont) \
 674                 (BN_set_word(r, (w)) && BN_to_montgomery(r, r, (mont), ctx))
 675
 676         bn_check_top(p);
 677         bn_check_top(m);
 678
 679         if (!(m->d[0] & 1))
 680                 {
 681                 BNerr(BN_F_BN_MOD_EXP_MONT_WORD,BN_R_CALLED_WITH_EVEN_MODULUS);
 682                 return(0);
 683                 }
 684         bits = BN_num_bits(p);
 685         if (bits == 0)
 686                 {
 687                 BN_one(rr);
 688                 return(1);
 689                 }
 690         BN_CTX_start(ctx);
 691         d = BN_CTX_get(ctx);
 692         r = BN_CTX_get(ctx);
 693         t = BN_CTX_get(ctx);
 694         if (d == NULL || r == NULL || t == NULL) goto err;
 695
 696 #ifdef ATALLA
 697         if (!tried_atalla)
 698                 {
 699                 BN_set_word(t, a);
 700                 if (BN_mod_exp_atalla(rr, t, p, m))
 701                         {
 702                         BN_CTX_end(ctx);
 703                         return 1;
 704                         }
 705                 }
 706 /* If it fails, try the other methods */
 707 #endif
 708
 709         if (in_mont != NULL)
 710                 mont=in_mont;
 711         else
 712                 {
 713                 if ((mont = BN_MONT_CTX_new()) == NULL) goto err;
 714                 if (!BN_MONT_CTX_set(mont, m, ctx)) goto err;
 715                 }
 716
 717         r_is_one = 1; /* except for Montgomery factor */
 718
 719         /* bits-1 >= 0 */
 720
 721         /* The result is accumulated in the product r*w. */
 722         w = a; /* bit 'bits-1' of 'p' is always set */
 723         for (b = bits-2; b >= 0; b--)
 724                 {
 725                 /* First, square r*w. */
 726                 next_w = w*w;
 727                 if ((next_w/w) != w) /* overflow */
 728                         {
 729                         if (r_is_one)
 730                                 {
 731                                 if (!BN_TO_MONTGOMERY_WORD(r, w, mont)) goto err;
 732                                 r_is_one = 0;
 733                                 }
 734                         else
 735                                 {
 736                                 if (!BN_MOD_MUL_WORD(r, w, m)) goto err;
 737                                 }
 738                         next_w = 1;
 739                         }
 740                 w = next_w;
 741                 if (!r_is_one)
 742                         {
 743                         if (!BN_mod_mul_montgomery(r, r, r, mont, ctx)) goto err;
 744                         }
 745
 746                 /* Second, multiply r*w by 'a' if exponent bit is set. */
 747                 if (BN_is_bit_set(p, b))
 748                         {
 749                         next_w = w*a;
 750                         if ((next_w/a) != w) /* overflow */
 751                                 {
 752                                 if (r_is_one)
 753                                         {
 754                                         if (!BN_TO_MONTGOMERY_WORD(r, w, mont)) goto err;
 755                                         r_is_one = 0;
 756                                         }
 757                                 else
 758                                         {
 759                                         if (!BN_MOD_MUL_WORD(r, w, m)) goto err;
 760                                         }
 761                                 next_w = a;
 762                                 }
 763                         w = next_w;
 764                         }
 765                 }
 766
 767         /* Finally, set r:=r*w. */
 768         if (w != 1)
 769                 {
 770                 if (r_is_one)
 771                         {
 772                         if (!BN_TO_MONTGOMERY_WORD(r, w, mont)) goto err;
 773                         r_is_one = 0;
 774                         }
 775                 else
 776                         {
 777                         if (!BN_MOD_MUL_WORD(r, w, m)) goto err;
 778                         }
 779                 }
 780
 781         if (r_is_one) /* can happen only if a == 1*/
 782                 {
 783                 if (!BN_one(rr)) goto err;
 784                 }
 785         else
 786                 {
 787                 if (!BN_from_montgomery(rr, r, mont, ctx)) goto err;
 788                 }
 789         ret = 1;
 790 err:
 791         if ((in_mont == NULL) && (mont != NULL)) BN_MONT_CTX_free(mont);
 792         BN_CTX_end(ctx);
 793         return(ret);
 794         }
 795
 796
 797 /* The old fallback, simple version :-) */
 798 int BN_mod_exp_simple(BIGNUM *r, BIGNUM *a, BIGNUM *p, BIGNUM *m,
 799              BN_CTX *ctx)
 800         {
 801         int i,j,bits,ret=0,wstart,wend,window,wvalue,ts=0;
 802         int start=1;
 803         BIGNUM *d;
 804         BIGNUM val[TABLE_SIZE];
 805
 806         bits=BN_num_bits(p);
 807
 808         if (bits == 0)
 809                 {
 810                 BN_one(r);
 811                 return(1);
 812                 }
 813
 814         BN_CTX_start(ctx);
 815         if ((d = BN_CTX_get(ctx)) == NULL) goto err;
 816
 817         BN_init(&(val[0]));
 818         ts=1;
 819         if (!BN_mod(&(val[0]),a,m,ctx)) goto err;               /* 1 */
 820
 821         window = BN_window_bits_for_exponent_size(bits);
 822         if (window > 1)
 823                 {
 824                 if (!BN_mod_mul(d,&(val[0]),&(val[0]),m,ctx))
 825                         goto err;                               /* 2 */
 826                 j=1<<(window-1);
 827                 for (i=1; i<j; i++)
 828                         {
 829                         BN_init(&(val[i]));
 830                         if (!BN_mod_mul(&(val[i]),&(val[i-1]),d,m,ctx))
 831                                 goto err;
 832                         }
 833                 ts=i;
 834                 }
 835
 836         start=1;        /* This is used to avoid multiplication etc
 837                          * when there is only the value '1' in the
 838                          * buffer. */
 839         wvalue=0;       /* The 'value' of the window */
 840         wstart=bits-1;  /* The top bit of the window */
 841         wend=0;         /* The bottom bit of the window */
 842
 843         if (!BN_one(r)) goto err;
 844
 845         for (;;)
 846                 {
 847                 if (BN_is_bit_set(p,wstart) == 0)
 848                         {
 849                         if (!start)
 850                                 if (!BN_mod_mul(r,r,r,m,ctx))
 851                                 goto err;
 852                         if (wstart == 0) break;
 853                         wstart--;
 854                         continue;
 855                         }
 856                 /* We now have wstart on a 'set' bit, we now need to work out
 857                  * how bit a window to do.  To do this we need to scan
 858                  * forward until the last set bit before the end of the
 859                  * window */
 860                 j=wstart;
 861                 wvalue=1;
 862                 wend=0;
 863                 for (i=1; i<window; i++)
 864                         {
 865                         if (wstart-i < 0) break;
 866                         if (BN_is_bit_set(p,wstart-i))
 867                                 {
 868                                 wvalue<<=(i-wend);
 869                                 wvalue|=1;
 870                                 wend=i;
 871                                 }
 872                         }
 873
 874                 /* wend is the size of the current window */
 875                 j=wend+1;
 876                 /* add the 'bytes above' */
 877                 if (!start)
 878                         for (i=0; i<j; i++)
 879                                 {
 880                                 if (!BN_mod_mul(r,r,r,m,ctx))
 881                                         goto err;
 882                                 }
 883
 884                 /* wvalue will be an odd number < 2^window */
 885                 if (!BN_mod_mul(r,r,&(val[wvalue>>1]),m,ctx))
 886                         goto err;
 887
 888                 /* move the 'window' down further */
 889                 wstart-=wend+1;
 890                 wvalue=0;
 891                 start=0;
 892                 if (wstart < 0) break;
 893                 }
 894         ret=1;
 895 err:
 896         BN_CTX_end(ctx);
 897         for (i=0; i<ts; i++)
 898                 BN_clear_free(&(val[i]));
 899         return(ret);
 900         }
 901