crypto/bn/bn_mont.c

   1 /* crypto/bn/bn_mont.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) 1998-2006 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  * Details about Montgomery multiplication algorithms can be found at
 114  * http://security.ece.orst.edu/publications.html, e.g.
 115  * http://security.ece.orst.edu/koc/papers/j37acmon.pdf and
 116  * sections 3.8 and 4.2 in http://security.ece.orst.edu/koc/papers/r01rsasw.pdf
 117  */
 118
 119 #define OPENSSL_FIPSAPI
 120
 121 #include <stdio.h>
 122 #include "cryptlib.h"
 123 #include "bn_lcl.h"
 124
 125 #define MONT_WORD /* use the faster word-based algorithm */
 126
 127 #ifdef MONT_WORD
 128 static int BN_from_montgomery_word(BIGNUM *ret, BIGNUM *r, BN_MONT_CTX *mont);
 129 #endif
 130
 131 int BN_mod_mul_montgomery(BIGNUM *r, const BIGNUM *a, const BIGNUM *b,
 132                           BN_MONT_CTX *mont, BN_CTX *ctx)
 133         {
 134         BIGNUM *tmp;
 135         int ret=0;
 136 #if defined(OPENSSL_BN_ASM_MONT) && defined(MONT_WORD)
 137         int num = mont->N.top;
 138
 139         if (num>1 && a->top==num && b->top==num)
 140                 {
 141                 if (bn_wexpand(r,num) == NULL) return(0);
 142                 if (bn_mul_mont(r->d,a->d,b->d,mont->N.d,mont->n0,num))
 143                         {
 144                         r->neg = a->neg^b->neg;
 145                         r->top = num;
 146                         bn_correct_top(r);
 147                         return(1);
 148                         }
 149                 }
 150 #endif
 151
 152         BN_CTX_start(ctx);
 153         tmp = BN_CTX_get(ctx);
 154         if (tmp == NULL) goto err;
 155
 156         bn_check_top(tmp);
 157         if (a == b)
 158                 {
 159                 if (!BN_sqr(tmp,a,ctx)) goto err;
 160                 }
 161         else
 162                 {
 163                 if (!BN_mul(tmp,a,b,ctx)) goto err;
 164                 }
 165         /* reduce from aRR to aR */
 166 #ifdef MONT_WORD
 167         if (!BN_from_montgomery_word(r,tmp,mont)) goto err;
 168 #else
 169         if (!BN_from_montgomery(r,tmp,mont,ctx)) goto err;
 170 #endif
 171         bn_check_top(r);
 172         ret=1;
 173 err:
 174         BN_CTX_end(ctx);
 175         return(ret);
 176         }
 177
 178 #ifdef MONT_WORD
 179 static int BN_from_montgomery_word(BIGNUM *ret, BIGNUM *r, BN_MONT_CTX *mont)
 180         {
 181         BIGNUM *n;
 182         BN_ULONG *ap,*np,*rp,n0,v,*nrp;
 183         int al,nl,max,i,x,ri;
 184
 185         n= &(mont->N);
 186         /* mont->ri is the size of mont->N in bits (rounded up
 187            to the word size) */
 188         al=ri=mont->ri/BN_BITS2;
 189
 190         nl=n->top;
 191         if ((al == 0) || (nl == 0)) { ret->top=0; return(1); }
 192
 193         max=(nl+al+1); /* allow for overflow (no?) XXX */
 194         if (bn_wexpand(r,max) == NULL) return(0);
 195
 196         r->neg^=n->neg;
 197         np=n->d;
 198         rp=r->d;
 199         nrp= &(r->d[nl]);
 200
 201         /* clear the top words of T */
 202 #if 1
 203         for (i=r->top; i<max; i++) /* memset? XXX */
 204                 r->d[i]=0;
 205 #else
 206         memset(&(r->d[r->top]),0,(max-r->top)*sizeof(BN_ULONG));
 207 #endif
 208
 209         r->top=max;
 210         n0=mont->n0[0];
 211
 212 #ifdef BN_COUNT
 213         fprintf(stderr,"word BN_from_montgomery_word %d * %d\n",nl,nl);
 214 #endif
 215         for (i=0; i<nl; i++)
 216                 {
 217 #ifdef __TANDEM
 218                 {
 219                    long long t1;
 220                    long long t2;
 221                    long long t3;
 222                    t1 = rp[0] * (n0 & 0177777);
 223                    t2 = 037777600000l;
 224                    t2 = n0 & t2;
 225                    t3 = rp[0] & 0177777;
 226                    t2 = (t3 * t2) & BN_MASK2;
 227                    t1 = t1 + t2;
 228                    v=bn_mul_add_words(rp,np,nl,(BN_ULONG) t1);
 229                 }
 230 #else
 231                 v=bn_mul_add_words(rp,np,nl,(rp[0]*n0)&BN_MASK2);
 232 #endif
 233                 nrp++;
 234                 rp++;
 235                 if (((nrp[-1]+=v)&BN_MASK2) >= v)
 236                         continue;
 237                 else
 238                         {
 239                         if (((++nrp[0])&BN_MASK2) != 0) continue;
 240                         if (((++nrp[1])&BN_MASK2) != 0) continue;
 241                         for (x=2; (((++nrp[x])&BN_MASK2) == 0); x++) ;
 242                         }
 243                 }
 244         bn_correct_top(r);
 245
 246         /* mont->ri will be a multiple of the word size and below code
 247          * is kind of BN_rshift(ret,r,mont->ri) equivalent */
 248         if (r->top <= ri)
 249                 {
 250                 ret->top=0;
 251                 return(1);
 252                 }
 253         al=r->top-ri;
 254
 255 #define BRANCH_FREE 1
 256 #if BRANCH_FREE
 257         if (bn_wexpand(ret,ri) == NULL) return(0);
 258         x=0-(((al-ri)>>(sizeof(al)*8-1))&1);
 259         ret->top=x=(ri&~x)|(al&x);      /* min(ri,al) */
 260         ret->neg=r->neg;
 261
 262         rp=ret->d;
 263         ap=&(r->d[ri]);
 264
 265         {
 266         size_t m1,m2;
 267
 268         v=bn_sub_words(rp,ap,np,ri);
 269         /* this ----------------^^ works even in al<ri case
 270          * thanks to zealous zeroing of top of the vector in the
 271          * beginning. */
 272
 273         /* if (al==ri && !v) || al>ri) nrp=rp; else nrp=ap; */
 274         /* in other words if subtraction result is real, then
 275          * trick unconditional memcpy below to perform in-place
 276          * "refresh" instead of actual copy. */
 277         m1=0-(size_t)(((al-ri)>>(sizeof(al)*8-1))&1);   /* al<ri */
 278         m2=0-(size_t)(((ri-al)>>(sizeof(al)*8-1))&1);   /* al>ri */
 279         m1|=m2;                 /* (al!=ri) */
 280         m1|=(0-(size_t)v);      /* (al!=ri || v) */
 281         m1&=~m2;                /* (al!=ri || v) && !al>ri */
 282         nrp=(BN_ULONG *)(((size_t)rp&~m1)|((size_t)ap&m1));
 283         }
 284
 285         /* 'i<ri' is chosen to eliminate dependency on input data, even
 286          * though it results in redundant copy in al<ri case. */
 287         for (i=0,ri-=4; i<ri; i+=4)
 288                 {
 289                 BN_ULONG t1,t2,t3,t4;
 290
 291                 t1=nrp[i+0];
 292                 t2=nrp[i+1];
 293                 t3=nrp[i+2];    ap[i+0]=0;
 294                 t4=nrp[i+3];    ap[i+1]=0;
 295                 rp[i+0]=t1;     ap[i+2]=0;
 296                 rp[i+1]=t2;     ap[i+3]=0;
 297                 rp[i+2]=t3;
 298                 rp[i+3]=t4;
 299                 }
 300         for (ri+=4; i<ri; i++)
 301                 rp[i]=nrp[i], ap[i]=0;
 302         bn_correct_top(r);
 303         bn_correct_top(ret);
 304 #else
 305         if (bn_wexpand(ret,al) == NULL) return(0);
 306         ret->top=al;
 307         ret->neg=r->neg;
 308
 309         rp=ret->d;
 310         ap=&(r->d[ri]);
 311         al-=4;
 312         for (i=0; i<al; i+=4)
 313                 {
 314                 BN_ULONG t1,t2,t3,t4;
 315
 316                 t1=ap[i+0];
 317                 t2=ap[i+1];
 318                 t3=ap[i+2];
 319                 t4=ap[i+3];
 320                 rp[i+0]=t1;
 321                 rp[i+1]=t2;
 322                 rp[i+2]=t3;
 323                 rp[i+3]=t4;
 324                 }
 325         al+=4;
 326         for (; i<al; i++)
 327                 rp[i]=ap[i];
 328
 329         if (BN_ucmp(ret, &(mont->N)) >= 0)
 330                 {
 331                 if (!BN_usub(ret,ret,&(mont->N))) return(0);
 332                 }
 333 #endif
 334         bn_check_top(ret);
 335
 336         return(1);
 337         }
 338 #endif  /* MONT_WORD */
 339
 340 int BN_from_montgomery(BIGNUM *ret, const BIGNUM *a, BN_MONT_CTX *mont,
 341              BN_CTX *ctx)
 342         {
 343         int retn=0;
 344 #ifdef MONT_WORD
 345         BIGNUM *t;
 346
 347         BN_CTX_start(ctx);
 348         if ((t = BN_CTX_get(ctx)) && BN_copy(t,a))
 349                 retn = BN_from_montgomery_word(ret,t,mont);
 350         BN_CTX_end(ctx);
 351 #else /* !MONT_WORD */
 352         BIGNUM *t1,*t2;
 353
 354         BN_CTX_start(ctx);
 355         t1 = BN_CTX_get(ctx);
 356         t2 = BN_CTX_get(ctx);
 357         if (t1 == NULL || t2 == NULL) goto err;
 358
 359         if (!BN_copy(t1,a)) goto err;
 360         BN_mask_bits(t1,mont->ri);
 361
 362         if (!BN_mul(t2,t1,&mont->Ni,ctx)) goto err;
 363         BN_mask_bits(t2,mont->ri);
 364
 365         if (!BN_mul(t1,t2,&mont->N,ctx)) goto err;
 366         if (!BN_add(t2,a,t1)) goto err;
 367         if (!BN_rshift(ret,t2,mont->ri)) goto err;
 368
 369         if (BN_ucmp(ret, &(mont->N)) >= 0)
 370                 {
 371                 if (!BN_usub(ret,ret,&(mont->N))) goto err;
 372                 }
 373         retn=1;
 374         bn_check_top(ret);
 375  err:
 376         BN_CTX_end(ctx);
 377 #endif /* MONT_WORD */
 378         return(retn);
 379         }
 380
 381 BN_MONT_CTX *BN_MONT_CTX_new(void)
 382         {
 383         BN_MONT_CTX *ret;
 384
 385         if ((ret=(BN_MONT_CTX *)OPENSSL_malloc(sizeof(BN_MONT_CTX))) == NULL)
 386                 return(NULL);
 387
 388         BN_MONT_CTX_init(ret);
 389         ret->flags=BN_FLG_MALLOCED;
 390         return(ret);
 391         }
 392
 393 void BN_MONT_CTX_init(BN_MONT_CTX *ctx)
 394         {
 395         ctx->ri=0;
 396         BN_init(&(ctx->RR));
 397         BN_init(&(ctx->N));
 398         BN_init(&(ctx->Ni));
 399         ctx->n0[0] = ctx->n0[1] = 0;
 400         ctx->flags=0;
 401         }
 402
 403 void BN_MONT_CTX_free(BN_MONT_CTX *mont)
 404         {
 405         if(mont == NULL)
 406             return;
 407
 408         BN_free(&(mont->RR));
 409         BN_free(&(mont->N));
 410         BN_free(&(mont->Ni));
 411         if (mont->flags & BN_FLG_MALLOCED)
 412                 OPENSSL_free(mont);
 413         }
 414
 415 int BN_MONT_CTX_set(BN_MONT_CTX *mont, const BIGNUM *mod, BN_CTX *ctx)
 416         {
 417         int ret = 0;
 418         BIGNUM *Ri,*R;
 419
 420         BN_CTX_start(ctx);
 421         if((Ri = BN_CTX_get(ctx)) == NULL) goto err;
 422         R= &(mont->RR);                                 /* grab RR as a temp */
 423         if (!BN_copy(&(mont->N),mod)) goto err;         /* Set N */
 424         mont->N.neg = 0;
 425
 426 #ifdef MONT_WORD
 427                 {
 428                 BIGNUM tmod;
 429                 BN_ULONG buf[2];
 430
 431                 BN_init(&tmod);
 432                 tmod.d=buf;
 433                 tmod.dmax=2;
 434                 tmod.neg=0;
 435
 436                 mont->ri=(BN_num_bits(mod)+(BN_BITS2-1))/BN_BITS2*BN_BITS2;
 437
 438 #if defined(OPENSSL_BN_ASM_MONT) && (BN_BITS2<=32)
 439                 /* Only certain BN_BITS2<=32 platforms actually make use of
 440                  * n0[1], and we could use the #else case (with a shorter R
 441                  * value) for the others.  However, currently only the assembler
 442                  * files do know which is which. */
 443
 444                 BN_zero(R);
 445                 if (!(BN_set_bit(R,2*BN_BITS2))) goto err;
 446
 447                                                                 tmod.top=0;
 448                 if ((buf[0] = mod->d[0]))                       tmod.top=1;
 449                 if ((buf[1] = mod->top>1 ? mod->d[1] : 0))      tmod.top=2;
 450
 451                 if ((BN_mod_inverse(Ri,R,&tmod,ctx)) == NULL)
 452                         goto err;
 453                 if (!BN_lshift(Ri,Ri,2*BN_BITS2)) goto err; /* R*Ri */
 454                 if (!BN_is_zero(Ri))
 455                         {
 456                         if (!BN_sub_word(Ri,1)) goto err;
 457                         }
 458                 else /* if N mod word size == 1 */
 459                         {
 460                         if (bn_expand(Ri,(int)sizeof(BN_ULONG)*2) == NULL)
 461                                 goto err;
 462                         /* Ri-- (mod double word size) */
 463                         Ri->neg=0;
 464                         Ri->d[0]=BN_MASK2;
 465                         Ri->d[1]=BN_MASK2;
 466                         Ri->top=2;
 467                         }
 468                 if (!BN_div(Ri,NULL,Ri,&tmod,ctx)) goto err;
 469                 /* Ni = (R*Ri-1)/N,
 470                  * keep only couple of least significant words: */
 471                 mont->n0[0] = (Ri->top > 0) ? Ri->d[0] : 0;
 472                 mont->n0[1] = (Ri->top > 1) ? Ri->d[1] : 0;
 473 #else
 474                 BN_zero(R);
 475                 if (!(BN_set_bit(R,BN_BITS2))) goto err;        /* R */
 476
 477                 buf[0]=mod->d[0]; /* tmod = N mod word size */
 478                 buf[1]=0;
 479                 tmod.top = buf[0] != 0 ? 1 : 0;
 480                                                         /* Ri = R^-1 mod N*/
 481                 if ((BN_mod_inverse(Ri,R,&tmod,ctx)) == NULL)
 482                         goto err;
 483                 if (!BN_lshift(Ri,Ri,BN_BITS2)) goto err; /* R*Ri */
 484                 if (!BN_is_zero(Ri))
 485                         {
 486                         if (!BN_sub_word(Ri,1)) goto err;
 487                         }
 488                 else /* if N mod word size == 1 */
 489                         {
 490                         if (!BN_set_word(Ri,BN_MASK2)) goto err;  /* Ri-- (mod word size) */
 491                         }
 492                 if (!BN_div(Ri,NULL,Ri,&tmod,ctx)) goto err;
 493                 /* Ni = (R*Ri-1)/N,
 494                  * keep only least significant word: */
 495                 mont->n0[0] = (Ri->top > 0) ? Ri->d[0] : 0;
 496                 mont->n0[1] = 0;
 497 #endif
 498                 }
 499 #else /* !MONT_WORD */
 500                 { /* bignum version */
 501                 mont->ri=BN_num_bits(&mont->N);
 502                 BN_zero(R);
 503                 if (!BN_set_bit(R,mont->ri)) goto err;  /* R = 2^ri */
 504                                                         /* Ri = R^-1 mod N*/
 505                 if ((BN_mod_inverse(Ri,R,&mont->N,ctx)) == NULL)
 506                         goto err;
 507                 if (!BN_lshift(Ri,Ri,mont->ri)) goto err; /* R*Ri */
 508                 if (!BN_sub_word(Ri,1)) goto err;
 509                                                         /* Ni = (R*Ri-1) / N */
 510                 if (!BN_div(&(mont->Ni),NULL,Ri,&mont->N,ctx)) goto err;
 511                 }
 512 #endif
 513
 514         /* setup RR for conversions */
 515         BN_zero(&(mont->RR));
 516         if (!BN_set_bit(&(mont->RR),mont->ri*2)) goto err;
 517         if (!BN_mod(&(mont->RR),&(mont->RR),&(mont->N),ctx)) goto err;
 518
 519         ret = 1;
 520 err:
 521         BN_CTX_end(ctx);
 522         return ret;
 523         }
 524
 525 BN_MONT_CTX *BN_MONT_CTX_copy(BN_MONT_CTX *to, BN_MONT_CTX *from)
 526         {
 527         if (to == from) return(to);
 528
 529         if (!BN_copy(&(to->RR),&(from->RR))) return NULL;
 530         if (!BN_copy(&(to->N),&(from->N))) return NULL;
 531         if (!BN_copy(&(to->Ni),&(from->Ni))) return NULL;
 532         to->ri=from->ri;
 533         to->n0[0]=from->n0[0];
 534         to->n0[1]=from->n0[1];
 535         return(to);
 536         }
 537
 538 BN_MONT_CTX *BN_MONT_CTX_set_locked(BN_MONT_CTX **pmont, int lock,
 539                                         const BIGNUM *mod, BN_CTX *ctx)
 540         {
 541         int got_write_lock = 0;
 542         BN_MONT_CTX *ret;
 543
 544         CRYPTO_r_lock(lock);
 545         if (!*pmont)
 546                 {
 547                 CRYPTO_r_unlock(lock);
 548                 CRYPTO_w_lock(lock);
 549                 got_write_lock = 1;
 550
 551                 if (!*pmont)
 552                         {
 553                         ret = BN_MONT_CTX_new();
 554                         if (ret && !BN_MONT_CTX_set(ret, mod, ctx))
 555                                 BN_MONT_CTX_free(ret);
 556                         else
 557                                 *pmont = ret;
 558                         }
 559                 }
 560
 561         ret = *pmont;
 562
 563         if (got_write_lock)
 564                 CRYPTO_w_unlock(lock);
 565         else
 566                 CRYPTO_r_unlock(lock);
 567
 568         return ret;
 569         }