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      1 /* crypto/bn/bn_mont.c */
      2 /* Copyright (C) 1995-1998 Eric Young (eay (at) cryptsoft.com)
      3  * All rights reserved.
      4  *
      5  * This package is an SSL implementation written
      6  * by Eric Young (eay (at) 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 (at) 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 (at) 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 (at) 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 (at) 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 (at) cryptsoft.com).  This product includes software written by Tim
    108  * Hudson (tjh (at) 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 #include <stdio.h>
    120 #include "cryptlib.h"
    121 #include "bn_lcl.h"
    122 
    123 #define MONT_WORD /* use the faster word-based algorithm */
    124 
    125 #ifdef MONT_WORD
    126 static int BN_from_montgomery_word(BIGNUM *ret, BIGNUM *r, BN_MONT_CTX *mont);
    127 #endif
    128 
    129 int BN_mod_mul_montgomery(BIGNUM *r, const BIGNUM *a, const BIGNUM *b,
    130 			  BN_MONT_CTX *mont, BN_CTX *ctx)
    131 	{
    132 	BIGNUM *tmp;
    133 	int ret=0;
    134 #if defined(OPENSSL_BN_ASM_MONT) && defined(MONT_WORD)
    135 	int num = mont->N.top;
    136 
    137 	if (num>1 && a->top==num && b->top==num)
    138 		{
    139 		if (bn_wexpand(r,num) == NULL) return(0);
    140 		if (bn_mul_mont(r->d,a->d,b->d,mont->N.d,mont->n0,num))
    141 			{
    142 			r->neg = a->neg^b->neg;
    143 			r->top = num;
    144 			bn_correct_top(r);
    145 			return(1);
    146 			}
    147 		}
    148 #endif
    149 
    150 	BN_CTX_start(ctx);
    151 	tmp = BN_CTX_get(ctx);
    152 	if (tmp == NULL) goto err;
    153 
    154 	bn_check_top(tmp);
    155 	if (a == b)
    156 		{
    157 		if (!BN_sqr(tmp,a,ctx)) goto err;
    158 		}
    159 	else
    160 		{
    161 		if (!BN_mul(tmp,a,b,ctx)) goto err;
    162 		}
    163 	/* reduce from aRR to aR */
    164 #ifdef MONT_WORD
    165 	if (!BN_from_montgomery_word(r,tmp,mont)) goto err;
    166 #else
    167 	if (!BN_from_montgomery(r,tmp,mont,ctx)) goto err;
    168 #endif
    169 	bn_check_top(r);
    170 	ret=1;
    171 err:
    172 	BN_CTX_end(ctx);
    173 	return(ret);
    174 	}
    175 
    176 #ifdef MONT_WORD
    177 static int BN_from_montgomery_word(BIGNUM *ret, BIGNUM *r, BN_MONT_CTX *mont)
    178 	{
    179 	BIGNUM *n;
    180 	BN_ULONG *ap,*np,*rp,n0,v,*nrp;
    181 	int al,nl,max,i,x,ri;
    182 
    183 	n= &(mont->N);
    184 	/* mont->ri is the size of mont->N in bits (rounded up
    185 	   to the word size) */
    186 	al=ri=mont->ri/BN_BITS2;
    187 
    188 	nl=n->top;
    189 	if ((al == 0) || (nl == 0)) { ret->top=0; return(1); }
    190 
    191 	max=(nl+al+1); /* allow for overflow (no?) XXX */
    192 	if (bn_wexpand(r,max) == NULL) return(0);
    193 
    194 	r->neg^=n->neg;
    195 	np=n->d;
    196 	rp=r->d;
    197 	nrp= &(r->d[nl]);
    198 
    199 	/* clear the top words of T */
    200 #if 1
    201 	for (i=r->top; i<max; i++) /* memset? XXX */
    202 		r->d[i]=0;
    203 #else
    204 	memset(&(r->d[r->top]),0,(max-r->top)*sizeof(BN_ULONG));
    205 #endif
    206 
    207 	r->top=max;
    208 	n0=mont->n0[0];
    209 
    210 #ifdef BN_COUNT
    211 	fprintf(stderr,"word BN_from_montgomery_word %d * %d\n",nl,nl);
    212 #endif
    213 	for (i=0; i<nl; i++)
    214 		{
    215 #ifdef __TANDEM
    216                 {
    217                    long long t1;
    218                    long long t2;
    219                    long long t3;
    220                    t1 = rp[0] * (n0 & 0177777);
    221                    t2 = 037777600000l;
    222                    t2 = n0 & t2;
    223                    t3 = rp[0] & 0177777;
    224                    t2 = (t3 * t2) & BN_MASK2;
    225                    t1 = t1 + t2;
    226                    v=bn_mul_add_words(rp,np,nl,(BN_ULONG) t1);
    227                 }
    228 #else
    229 		v=bn_mul_add_words(rp,np,nl,(rp[0]*n0)&BN_MASK2);
    230 #endif
    231 		nrp++;
    232 		rp++;
    233 		if (((nrp[-1]+=v)&BN_MASK2) >= v)
    234 			continue;
    235 		else
    236 			{
    237 			if (((++nrp[0])&BN_MASK2) != 0) continue;
    238 			if (((++nrp[1])&BN_MASK2) != 0) continue;
    239 			for (x=2; (((++nrp[x])&BN_MASK2) == 0); x++) ;
    240 			}
    241 		}
    242 	bn_correct_top(r);
    243 
    244 	/* mont->ri will be a multiple of the word size and below code
    245 	 * is kind of BN_rshift(ret,r,mont->ri) equivalent */
    246 	if (r->top <= ri)
    247 		{
    248 		ret->top=0;
    249 		return(1);
    250 		}
    251 	al=r->top-ri;
    252 
    253 #define BRANCH_FREE 1
    254 #if BRANCH_FREE
    255 	if (bn_wexpand(ret,ri) == NULL) return(0);
    256 	x=0-(((al-ri)>>(sizeof(al)*8-1))&1);
    257 	ret->top=x=(ri&~x)|(al&x);	/* min(ri,al) */
    258 	ret->neg=r->neg;
    259 
    260 	rp=ret->d;
    261 	ap=&(r->d[ri]);
    262 
    263 	{
    264 	size_t m1,m2;
    265 
    266 	v=bn_sub_words(rp,ap,np,ri);
    267 	/* this ----------------^^ works even in al<ri case
    268 	 * thanks to zealous zeroing of top of the vector in the
    269 	 * beginning. */
    270 
    271 	/* if (al==ri && !v) || al>ri) nrp=rp; else nrp=ap; */
    272 	/* in other words if subtraction result is real, then
    273 	 * trick unconditional memcpy below to perform in-place
    274 	 * "refresh" instead of actual copy. */
    275 	m1=0-(size_t)(((al-ri)>>(sizeof(al)*8-1))&1);	/* al<ri */
    276 	m2=0-(size_t)(((ri-al)>>(sizeof(al)*8-1))&1);	/* al>ri */
    277 	m1|=m2;			/* (al!=ri) */
    278 	m1|=(0-(size_t)v);	/* (al!=ri || v) */
    279 	m1&=~m2;		/* (al!=ri || v) && !al>ri */
    280 	nrp=(BN_ULONG *)(((PTR_SIZE_INT)rp&~m1)|((PTR_SIZE_INT)ap&m1));
    281 	}
    282 
    283 	/* 'i<ri' is chosen to eliminate dependency on input data, even
    284 	 * though it results in redundant copy in al<ri case. */
    285 	for (i=0,ri-=4; i<ri; i+=4)
    286 		{
    287 		BN_ULONG t1,t2,t3,t4;
    288 
    289 		t1=nrp[i+0];
    290 		t2=nrp[i+1];
    291 		t3=nrp[i+2];	ap[i+0]=0;
    292 		t4=nrp[i+3];	ap[i+1]=0;
    293 		rp[i+0]=t1;	ap[i+2]=0;
    294 		rp[i+1]=t2;	ap[i+3]=0;
    295 		rp[i+2]=t3;
    296 		rp[i+3]=t4;
    297 		}
    298 	for (ri+=4; i<ri; i++)
    299 		rp[i]=nrp[i], ap[i]=0;
    300 	bn_correct_top(r);
    301 	bn_correct_top(ret);
    302 #else
    303 	if (bn_wexpand(ret,al) == NULL) return(0);
    304 	ret->top=al;
    305 	ret->neg=r->neg;
    306 
    307 	rp=ret->d;
    308 	ap=&(r->d[ri]);
    309 	al-=4;
    310 	for (i=0; i<al; i+=4)
    311 		{
    312 		BN_ULONG t1,t2,t3,t4;
    313 
    314 		t1=ap[i+0];
    315 		t2=ap[i+1];
    316 		t3=ap[i+2];
    317 		t4=ap[i+3];
    318 		rp[i+0]=t1;
    319 		rp[i+1]=t2;
    320 		rp[i+2]=t3;
    321 		rp[i+3]=t4;
    322 		}
    323 	al+=4;
    324 	for (; i<al; i++)
    325 		rp[i]=ap[i];
    326 
    327 	if (BN_ucmp(ret, &(mont->N)) >= 0)
    328 		{
    329 		if (!BN_usub(ret,ret,&(mont->N))) return(0);
    330 		}
    331 #endif
    332 	bn_check_top(ret);
    333 
    334 	return(1);
    335 	}
    336 #endif	/* MONT_WORD */
    337 
    338 int BN_from_montgomery(BIGNUM *ret, const BIGNUM *a, BN_MONT_CTX *mont,
    339 	     BN_CTX *ctx)
    340 	{
    341 	int retn=0;
    342 #ifdef MONT_WORD
    343 	BIGNUM *t;
    344 
    345 	BN_CTX_start(ctx);
    346 	if ((t = BN_CTX_get(ctx)) && BN_copy(t,a))
    347 		retn = BN_from_montgomery_word(ret,t,mont);
    348 	BN_CTX_end(ctx);
    349 #else /* !MONT_WORD */
    350 	BIGNUM *t1,*t2;
    351 
    352 	BN_CTX_start(ctx);
    353 	t1 = BN_CTX_get(ctx);
    354 	t2 = BN_CTX_get(ctx);
    355 	if (t1 == NULL || t2 == NULL) goto err;
    356 
    357 	if (!BN_copy(t1,a)) goto err;
    358 	BN_mask_bits(t1,mont->ri);
    359 
    360 	if (!BN_mul(t2,t1,&mont->Ni,ctx)) goto err;
    361 	BN_mask_bits(t2,mont->ri);
    362 
    363 	if (!BN_mul(t1,t2,&mont->N,ctx)) goto err;
    364 	if (!BN_add(t2,a,t1)) goto err;
    365 	if (!BN_rshift(ret,t2,mont->ri)) goto err;
    366 
    367 	if (BN_ucmp(ret, &(mont->N)) >= 0)
    368 		{
    369 		if (!BN_usub(ret,ret,&(mont->N))) goto err;
    370 		}
    371 	retn=1;
    372 	bn_check_top(ret);
    373  err:
    374 	BN_CTX_end(ctx);
    375 #endif /* MONT_WORD */
    376 	return(retn);
    377 	}
    378 
    379 BN_MONT_CTX *BN_MONT_CTX_new(void)
    380 	{
    381 	BN_MONT_CTX *ret;
    382 
    383 	if ((ret=(BN_MONT_CTX *)OPENSSL_malloc(sizeof(BN_MONT_CTX))) == NULL)
    384 		return(NULL);
    385 
    386 	BN_MONT_CTX_init(ret);
    387 	ret->flags=BN_FLG_MALLOCED;
    388 	return(ret);
    389 	}
    390 
    391 void BN_MONT_CTX_init(BN_MONT_CTX *ctx)
    392 	{
    393 	ctx->ri=0;
    394 	BN_init(&(ctx->RR));
    395 	BN_init(&(ctx->N));
    396 	BN_init(&(ctx->Ni));
    397 	ctx->n0[0] = ctx->n0[1] = 0;
    398 	ctx->flags=0;
    399 	}
    400 
    401 void BN_MONT_CTX_free(BN_MONT_CTX *mont)
    402 	{
    403 	if(mont == NULL)
    404 	    return;
    405 
    406 	BN_free(&(mont->RR));
    407 	BN_free(&(mont->N));
    408 	BN_free(&(mont->Ni));
    409 	if (mont->flags & BN_FLG_MALLOCED)
    410 		OPENSSL_free(mont);
    411 	}
    412 
    413 int BN_MONT_CTX_set(BN_MONT_CTX *mont, const BIGNUM *mod, BN_CTX *ctx)
    414 	{
    415 	int ret = 0;
    416 	BIGNUM *Ri,*R;
    417 
    418 	BN_CTX_start(ctx);
    419 	if((Ri = BN_CTX_get(ctx)) == NULL) goto err;
    420 	R= &(mont->RR);					/* grab RR as a temp */
    421 	if (!BN_copy(&(mont->N),mod)) goto err;		/* Set N */
    422 	mont->N.neg = 0;
    423 
    424 #ifdef MONT_WORD
    425 		{
    426 		BIGNUM tmod;
    427 		BN_ULONG buf[2];
    428 
    429 		BN_init(&tmod);
    430 		tmod.d=buf;
    431 		tmod.dmax=2;
    432 		tmod.neg=0;
    433 
    434 		mont->ri=(BN_num_bits(mod)+(BN_BITS2-1))/BN_BITS2*BN_BITS2;
    435 
    436 #if defined(OPENSSL_BN_ASM_MONT) && (BN_BITS2<=32)
    437 		/* Only certain BN_BITS2<=32 platforms actually make use of
    438 		 * n0[1], and we could use the #else case (with a shorter R
    439 		 * value) for the others.  However, currently only the assembler
    440 		 * files do know which is which. */
    441 
    442 		BN_zero(R);
    443 		if (!(BN_set_bit(R,2*BN_BITS2))) goto err;
    444 
    445 								tmod.top=0;
    446 		if ((buf[0] = mod->d[0]))			tmod.top=1;
    447 		if ((buf[1] = mod->top>1 ? mod->d[1] : 0))	tmod.top=2;
    448 
    449 		if ((BN_mod_inverse(Ri,R,&tmod,ctx)) == NULL)
    450 			goto err;
    451 		if (!BN_lshift(Ri,Ri,2*BN_BITS2)) goto err; /* R*Ri */
    452 		if (!BN_is_zero(Ri))
    453 			{
    454 			if (!BN_sub_word(Ri,1)) goto err;
    455 			}
    456 		else /* if N mod word size == 1 */
    457 			{
    458 			if (bn_expand(Ri,(int)sizeof(BN_ULONG)*2) == NULL)
    459 				goto err;
    460 			/* Ri-- (mod double word size) */
    461 			Ri->neg=0;
    462 			Ri->d[0]=BN_MASK2;
    463 			Ri->d[1]=BN_MASK2;
    464 			Ri->top=2;
    465 			}
    466 		if (!BN_div(Ri,NULL,Ri,&tmod,ctx)) goto err;
    467 		/* Ni = (R*Ri-1)/N,
    468 		 * keep only couple of least significant words: */
    469 		mont->n0[0] = (Ri->top > 0) ? Ri->d[0] : 0;
    470 		mont->n0[1] = (Ri->top > 1) ? Ri->d[1] : 0;
    471 #else
    472 		BN_zero(R);
    473 		if (!(BN_set_bit(R,BN_BITS2))) goto err;	/* R */
    474 
    475 		buf[0]=mod->d[0]; /* tmod = N mod word size */
    476 		buf[1]=0;
    477 		tmod.top = buf[0] != 0 ? 1 : 0;
    478 							/* Ri = R^-1 mod N*/
    479 		if ((BN_mod_inverse(Ri,R,&tmod,ctx)) == NULL)
    480 			goto err;
    481 		if (!BN_lshift(Ri,Ri,BN_BITS2)) goto err; /* R*Ri */
    482 		if (!BN_is_zero(Ri))
    483 			{
    484 			if (!BN_sub_word(Ri,1)) goto err;
    485 			}
    486 		else /* if N mod word size == 1 */
    487 			{
    488 			if (!BN_set_word(Ri,BN_MASK2)) goto err;  /* Ri-- (mod word size) */
    489 			}
    490 		if (!BN_div(Ri,NULL,Ri,&tmod,ctx)) goto err;
    491 		/* Ni = (R*Ri-1)/N,
    492 		 * keep only least significant word: */
    493 		mont->n0[0] = (Ri->top > 0) ? Ri->d[0] : 0;
    494 		mont->n0[1] = 0;
    495 #endif
    496 		}
    497 #else /* !MONT_WORD */
    498 		{ /* bignum version */
    499 		mont->ri=BN_num_bits(&mont->N);
    500 		BN_zero(R);
    501 		if (!BN_set_bit(R,mont->ri)) goto err;  /* R = 2^ri */
    502 		                                        /* Ri = R^-1 mod N*/
    503 		if ((BN_mod_inverse(Ri,R,&mont->N,ctx)) == NULL)
    504 			goto err;
    505 		if (!BN_lshift(Ri,Ri,mont->ri)) goto err; /* R*Ri */
    506 		if (!BN_sub_word(Ri,1)) goto err;
    507 							/* Ni = (R*Ri-1) / N */
    508 		if (!BN_div(&(mont->Ni),NULL,Ri,&mont->N,ctx)) goto err;
    509 		}
    510 #endif
    511 
    512 	/* setup RR for conversions */
    513 	BN_zero(&(mont->RR));
    514 	if (!BN_set_bit(&(mont->RR),mont->ri*2)) goto err;
    515 	if (!BN_mod(&(mont->RR),&(mont->RR),&(mont->N),ctx)) goto err;
    516 
    517 	ret = 1;
    518 err:
    519 	BN_CTX_end(ctx);
    520 	return ret;
    521 	}
    522 
    523 BN_MONT_CTX *BN_MONT_CTX_copy(BN_MONT_CTX *to, BN_MONT_CTX *from)
    524 	{
    525 	if (to == from) return(to);
    526 
    527 	if (!BN_copy(&(to->RR),&(from->RR))) return NULL;
    528 	if (!BN_copy(&(to->N),&(from->N))) return NULL;
    529 	if (!BN_copy(&(to->Ni),&(from->Ni))) return NULL;
    530 	to->ri=from->ri;
    531 	to->n0[0]=from->n0[0];
    532 	to->n0[1]=from->n0[1];
    533 	return(to);
    534 	}
    535 
    536 BN_MONT_CTX *BN_MONT_CTX_set_locked(BN_MONT_CTX **pmont, int lock,
    537 					const BIGNUM *mod, BN_CTX *ctx)
    538 	{
    539 	int got_write_lock = 0;
    540 	BN_MONT_CTX *ret;
    541 
    542 	CRYPTO_r_lock(lock);
    543 	if (!*pmont)
    544 		{
    545 		CRYPTO_r_unlock(lock);
    546 		CRYPTO_w_lock(lock);
    547 		got_write_lock = 1;
    548 
    549 		if (!*pmont)
    550 			{
    551 			ret = BN_MONT_CTX_new();
    552 			if (ret && !BN_MONT_CTX_set(ret, mod, ctx))
    553 				BN_MONT_CTX_free(ret);
    554 			else
    555 				*pmont = ret;
    556 			}
    557 		}
    558 
    559 	ret = *pmont;
    560 
    561 	if (got_write_lock)
    562 		CRYPTO_w_unlock(lock);
    563 	else
    564 		CRYPTO_r_unlock(lock);
    565 
    566 	return ret;
    567 	}
    568