X-Git-Url: https://git.openssl.org/?p=openssl.git;a=blobdiff_plain;f=crypto%2Fbn%2Fbn_mont.c;h=4339aab18761535ec53d1a875291d589fc165544;hp=e73b0cbb693df6c96fdba26c833cba7e4cf2a6cc;hb=5b89f78a89d0ca2cef778eea05da925875125771;hpb=1b3b0a54d1f9eafc0be0992a524cd84e2c1daf97

diff --git a/crypto/bn/bn_mont.c b/crypto/bn/bn_mont.c
index e73b0cbb69..4339aab187 100644
--- a/crypto/bn/bn_mont.c
+++ b/crypto/bn/bn_mont.c
@@ -55,225 +55,336 @@
  * copied and put under another distribution licence
  * [including the GNU Public Licence.]
  */
+/* ====================================================================
+ * Copyright (c) 1998-2006 The OpenSSL Project.  All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer. 
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * 3. All advertising materials mentioning features or use of this
+ *    software must display the following acknowledgment:
+ *    "This product includes software developed by the OpenSSL Project
+ *    for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
+ *
+ * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
+ *    endorse or promote products derived from this software without
+ *    prior written permission. For written permission, please contact
+ *    openssl-core@openssl.org.
+ *
+ * 5. Products derived from this software may not be called "OpenSSL"
+ *    nor may "OpenSSL" appear in their names without prior written
+ *    permission of the OpenSSL Project.
+ *
+ * 6. Redistributions of any form whatsoever must retain the following
+ *    acknowledgment:
+ *    "This product includes software developed by the OpenSSL Project
+ *    for use in the OpenSSL Toolkit (http://www.openssl.org/)"
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
+ * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE OpenSSL PROJECT OR
+ * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ * ====================================================================
+ *
+ * This product includes cryptographic software written by Eric Young
+ * (eay@cryptsoft.com).  This product includes software written by Tim
+ * Hudson (tjh@cryptsoft.com).
+ *
+ */
 
 /*
- * Details about Montgomery multiplication algorithms can be found at:
- * http://www.ece.orst.edu/ISL/Publications.html
- * http://www.ece.orst.edu/ISL/Koc/papers/j37acmon.pdf
+ * Details about Montgomery multiplication algorithms can be found at
+ * http://security.ece.orst.edu/publications.html, e.g.
+ * http://security.ece.orst.edu/koc/papers/j37acmon.pdf and
+ * sections 3.8 and 4.2 in http://security.ece.orst.edu/koc/papers/r01rsasw.pdf
  */
 
 #include <stdio.h>
 #include "cryptlib.h"
 #include "bn_lcl.h"
 
-#define MONT_WORD
+#define MONT_WORD /* use the faster word-based algorithm */
+
+#ifdef MONT_WORD
+static int BN_from_montgomery_word(BIGNUM *ret, BIGNUM *r, BN_MONT_CTX *mont);
+#endif
 
-int BN_mod_mul_montgomery(r,a,b,mont,ctx)
-BIGNUM *r,*a,*b;
-BN_MONT_CTX *mont;
-BN_CTX *ctx;
+int BN_mod_mul_montgomery(BIGNUM *r, const BIGNUM *a, const BIGNUM *b,
+			  BN_MONT_CTX *mont, BN_CTX *ctx)
 	{
-	BIGNUM *tmp,*tmp2;
+	BIGNUM *tmp;
+	int ret=0;
+#if defined(OPENSSL_BN_ASM_MONT) && defined(MONT_WORD)
+	int num = mont->N.top;
+
+	if (num>1 && a->top==num && b->top==num)
+		{
+		if (bn_wexpand(r,num) == NULL) return(0);
+		if (bn_mul_mont(r->d,a->d,b->d,mont->N.d,mont->n0,num))
+			{
+			r->neg = a->neg^b->neg;
+			r->top = num;
+			bn_correct_top(r);
+			return(1);
+			}
+		}
+#endif
 
-        tmp= &(ctx->bn[ctx->tos]);
-        tmp2= &(ctx->bn[ctx->tos]);
-	ctx->tos+=2;
+	BN_CTX_start(ctx);
+	tmp = BN_CTX_get(ctx);
+	if (tmp == NULL) goto err;
 
 	bn_check_top(tmp);
-	bn_check_top(tmp2);
-
 	if (a == b)
 		{
-#if 0
-		bn_wexpand(tmp,a->top*2);
-		bn_wexpand(tmp2,a->top*4);
-		bn_sqr_recursive(tmp->d,a->d,a->top,tmp2->d);
-		tmp->top=a->top*2;
-		if (tmp->d[tmp->top-1] == 0)
-			tmp->top--;
-#else
 		if (!BN_sqr(tmp,a,ctx)) goto err;
-#endif
 		}
 	else
 		{
 		if (!BN_mul(tmp,a,b,ctx)) goto err;
 		}
 	/* reduce from aRR to aR */
+#ifdef MONT_WORD
+	if (!BN_from_montgomery_word(r,tmp,mont)) goto err;
+#else
 	if (!BN_from_montgomery(r,tmp,mont,ctx)) goto err;
-	ctx->tos-=2;
-	return(1);
+#endif
+	bn_check_top(r);
+	ret=1;
 err:
-	return(0);
+	BN_CTX_end(ctx);
+	return(ret);
 	}
 
-int BN_from_montgomery(ret,a,mont,ctx)
-BIGNUM *ret;
-BIGNUM *a;
-BN_MONT_CTX *mont;
-BN_CTX *ctx;
+#ifdef MONT_WORD
+static int BN_from_montgomery_word(BIGNUM *ret, BIGNUM *r, BN_MONT_CTX *mont)
 	{
-#ifdef BN_RECURSION
-	if (mont->use_word)
-#endif
-		{
-		BIGNUM *n,*r;
-		BN_ULONG *ap,*np,*rp,n0,v,*nrp;
-		int al,nl,max,i,x,ri;
-		int retn=0;
+	BIGNUM *n;
+	BN_ULONG *ap,*np,*rp,n0,v,*nrp;
+	int al,nl,max,i,x,ri;
 
-		r= &(ctx->bn[ctx->tos]);
+	n= &(mont->N);
+	/* mont->ri is the size of mont->N in bits (rounded up
+	   to the word size) */
+	al=ri=mont->ri/BN_BITS2;
 
-		if (!BN_copy(r,a)) goto err1;
-		n= &(mont->N);
+	nl=n->top;
+	if ((al == 0) || (nl == 0)) { ret->top=0; return(1); }
 
-		ap=a->d;
-		/* mont->ri is the size of mont->N in bits/words */
-		al=ri=mont->ri/BN_BITS2;
+	max=(nl+al+1); /* allow for overflow (no?) XXX */
+	if (bn_wexpand(r,max) == NULL) return(0);
 
-		nl=n->top;
-		if ((al == 0) || (nl == 0)) { r->top=0; return(1); }
+	r->neg^=n->neg;
+	np=n->d;
+	rp=r->d;
+	nrp= &(r->d[nl]);
 
-		max=(nl+al+1); /* allow for overflow (no?) XXX */
-		if (bn_wexpand(r,max) == NULL) goto err1;
-		if (bn_wexpand(ret,max) == NULL) goto err1;
-
-		r->neg=a->neg^n->neg;
-		np=n->d;
-		rp=r->d;
-		nrp= &(r->d[nl]);
-
-		/* clear the top words of T */
+	/* clear the top words of T */
 #if 1
-		for (i=r->top; i<max; i++) /* memset? XXX */
-			r->d[i]=0;
+	for (i=r->top; i<max; i++) /* memset? XXX */
+		r->d[i]=0;
 #else
-		memset(&(r->d[r->top]),0,(max-r->top)*sizeof(BN_ULONG)); 
+	memset(&(r->d[r->top]),0,(max-r->top)*sizeof(BN_ULONG)); 
 #endif
 
-		r->top=max;
-		n0=mont->n0;
+	r->top=max;
+	n0=mont->n0[0];
 
 #ifdef BN_COUNT
-printf("word BN_from_montgomery %d * %d\n",nl,nl);
+	fprintf(stderr,"word BN_from_montgomery_word %d * %d\n",nl,nl);
 #endif
-		for (i=0; i<nl; i++)
-			{
-			v=bn_mul_add_words(rp,np,nl,(rp[0]*n0)&BN_MASK2);
-			nrp++;
-			rp++;
-			if (((nrp[-1]+=v)&BN_MASK2) >= v)
-				continue;
-			else
-				{
-				if (((++nrp[0])&BN_MASK2) != 0) continue;
-				if (((++nrp[1])&BN_MASK2) != 0) continue;
-				for (x=2; (((++nrp[x])&BN_MASK2) == 0); x++) ;
-				}
-			}
-		bn_fix_top(r);
-
-		/* mont->ri will be a multiple of the word size */
-#if 0
-		BN_rshift(ret,r,mont->ri);
+	for (i=0; i<nl; i++)
+		{
+#ifdef __TANDEM
+                {
+                   long long t1;
+                   long long t2;
+                   long long t3;
+                   t1 = rp[0] * (n0 & 0177777);
+                   t2 = 037777600000l;
+                   t2 = n0 & t2;
+                   t3 = rp[0] & 0177777;
+                   t2 = (t3 * t2) & BN_MASK2;
+                   t1 = t1 + t2;
+                   v=bn_mul_add_words(rp,np,nl,(BN_ULONG) t1);
+                }
 #else
-		x=ri;
-		rp=ret->d;
-		ap= &(r->d[x]);
-		if (r->top < x)
-			al=0;
+		v=bn_mul_add_words(rp,np,nl,(rp[0]*n0)&BN_MASK2);
+#endif
+		nrp++;
+		rp++;
+		if (((nrp[-1]+=v)&BN_MASK2) >= v)
+			continue;
 		else
-			al=r->top-x;
-		ret->top=al;
-		al-=4;
-		for (i=0; i<al; i+=4)
 			{
-			BN_ULONG t1,t2,t3,t4;
-
-			t1=ap[i+0];
-			t2=ap[i+1];
-			t3=ap[i+2];
-			t4=ap[i+3];
-			rp[i+0]=t1;
-			rp[i+1]=t2;
-			rp[i+2]=t3;
-			rp[i+3]=t4;
+			if (((++nrp[0])&BN_MASK2) != 0) continue;
+			if (((++nrp[1])&BN_MASK2) != 0) continue;
+			for (x=2; (((++nrp[x])&BN_MASK2) == 0); x++) ;
 			}
-		al+=4;
-		for (; i<al; i++)
-			rp[i]=ap[i];
-#endif
+		}
+	bn_correct_top(r);
 
-		if (BN_ucmp(ret, &(mont->N)) >= 0)
-			{
-			BN_usub(ret,ret,&(mont->N)); /* XXX */
-			}
-		retn=1;
-err1:
-		return(retn);
+	/* mont->ri will be a multiple of the word size and below code
+	 * is kind of BN_rshift(ret,r,mont->ri) equivalent */
+	if (r->top < ri)
+		{
+		ret->top=0;
+		return(1);
 		}
-#ifdef BN_RECURSION
-	else /* bignum version */ 
+	al=r->top-ri;
+
+#define BRANCH_FREE 1
+#if BRANCH_FREE
+	if (bn_wexpand(ret,ri) == NULL) return(0);
+	x=0-(((al-ri)>>(sizeof(al)*8-1))&1);
+	ret->top=x=(ri&~x)|(al&x);	/* min(ri,al) */
+	ret->neg=r->neg;
+
+	rp=ret->d;
+	ap=&(r->d[ri]);
+	nrp=ap;
+
+	/* This 'if' denotes violation of 2*M<r^(n-1) boundary condition
+	 * formulated by C.D.Walter in "Montgomery exponentiation needs
+	 * no final subtractions." Incurred branch can disclose only
+	 * information about modulus length, which is not really secret. */
+	if ((mont->N.d[ri-1]>>(BN_BITS2-2))!=0)
 		{
-		BIGNUM *t1,*t2,*t3;
-		int j,i;
-
-#ifdef BN_COUNT
-printf("number BN_from_montgomery\n");
-#endif
-
-		t1= &(ctx->bn[ctx->tos]);
-		t2= &(ctx->bn[ctx->tos+1]);
-		t3= &(ctx->bn[ctx->tos+2]);
-
-		i=mont->Ni.top;
-		bn_wexpand(ret,i); /* perhaps only i*2 */
-		bn_wexpand(t1,i*4); /* perhaps only i*2 */
-		bn_wexpand(t2,i*2); /* perhaps only i   */
-
-		bn_mul_low_recursive(t2->d,a->d,mont->Ni.d,i,t1->d);
+		size_t m1,m2;
+
+		v=bn_sub_words(rp,ap,mont->N.d,ri);
+		/* this -----------------------^^ works even in al<ri case
+		 * thanks to zealous zeroing of top of the vector in the
+		 * beginning. */
+
+		/* if (al==ri && !v) || al>ri) nrp=rp; else nrp=ap; */
+		/* in other words if subtraction result is real, then
+		 * trick unconditional memcpy below to perform in-place
+		 * "refresh" instead of actual copy. */
+		m1=0-(size_t)(((al-ri)>>(sizeof(al)*8-1))&1);	/* al<ri */
+		m2=0-(size_t)(((ri-al)>>(sizeof(al)*8-1))&1);	/* al>ri */
+		m1|=m2;			/* (al!=ri) */
+		m1|=(0-(size_t)v);	/* (al!=ri || v) */
+		m1&=~m2;		/* (al!=ri || v) && !al>ri */
+		nrp=(BN_ULONG *)(((size_t)rp&~m1)|((size_t)ap&m1));
+		}
 
-		BN_zero(t3);
-		BN_set_bit(t3,mont->N.top*BN_BITS2);
-		bn_sub_words(t3->d,t3->d,a->d,i);
-		bn_mul_high(ret->d,t2->d,mont->N.d,t3->d,i,t1->d);
+	/* 'i<ri' is chosen to eliminate dependency on input data, even
+	 * though it results in redundant copy in al<ri case. */
+	for (i=0,ri-=4; i<ri; i+=4)
+		{
+		BN_ULONG t1,t2,t3,t4;
+		
+		t1=nrp[i+0];
+		t2=nrp[i+1];
+		t3=nrp[i+2];	ap[i+0]=0;
+		t4=nrp[i+3];	ap[i+1]=0;
+		rp[i+0]=t1;	ap[i+2]=0;
+		rp[i+1]=t2;	ap[i+3]=0;
+		rp[i+2]=t3;
+		rp[i+3]=t4;
+		}
+	for (ri+=4; i<ri; i++)
+		rp[i]=nrp[i], ap[i]=0;
+#else
+	if (bn_wexpand(ret,al) == NULL) return(0);
+	ret->top=al;
+	ret->neg=r->neg;
+
+	rp=ret->d;
+	ap=&(r->d[ri]);
+	al-=4;
+	for (i=0; i<al; i+=4)
+		{
+		BN_ULONG t1,t2,t3,t4;
+		
+		t1=ap[i+0];
+		t2=ap[i+1];
+		t3=ap[i+2];
+		t4=ap[i+3];
+		rp[i+0]=t1;
+		rp[i+1]=t2;
+		rp[i+2]=t3;
+		rp[i+3]=t4;
+		}
+	al+=4;
+	for (; i<al; i++)
+		rp[i]=ap[i];
 
-		/* hmm... if a is between i and 2*i, things are bad */
-		if (a->top > i)
-			{
-			j=(int)(bn_add_words(ret->d,ret->d,&(a->d[i]),i));
-			if (j) /* overflow */
-				bn_sub_words(ret->d,ret->d,mont->N.d,i);
-			}
-		ret->top=i;
-		bn_fix_top(ret);
-		if (a->d[0])
-			BN_add_word(ret,1); /* Always? */
-		else	/* Very very rare */
-			{
-			for (i=1; i<mont->N.top-1; i++)
-				{
-				if (a->d[i])
-					{
-					BN_add_word(ret,1); /* Always? */
-					break;
-					}
-				}
-			}
+	if (BN_ucmp(ret, &(mont->N)) >= 0)
+		{
+		if (!BN_usub(ret,ret,&(mont->N))) return(0);
+		}
+#endif
+	bn_check_top(ret);
 
-		if (BN_ucmp(ret,&(mont->N)) >= 0)
-			BN_usub(ret,ret,&(mont->N));
+	return(1);
+	}
+#endif	/* MONT_WORD */
 
-		return(1);
+int BN_from_montgomery(BIGNUM *ret, const BIGNUM *a, BN_MONT_CTX *mont,
+	     BN_CTX *ctx)
+	{
+	int retn=0;
+#ifdef MONT_WORD
+	BIGNUM *t;
+
+	BN_CTX_start(ctx);
+	if ((t = BN_CTX_get(ctx)) && BN_copy(t,a))
+		retn = BN_from_montgomery_word(ret,t,mont);
+	BN_CTX_end(ctx);
+#else /* !MONT_WORD */
+	BIGNUM *t1,*t2;
+
+	BN_CTX_start(ctx);
+	t1 = BN_CTX_get(ctx);
+	t2 = BN_CTX_get(ctx);
+	if (t1 == NULL || t2 == NULL) goto err;
+	
+	if (!BN_copy(t1,a)) goto err;
+	BN_mask_bits(t1,mont->ri);
+
+	if (!BN_mul(t2,t1,&mont->Ni,ctx)) goto err;
+	BN_mask_bits(t2,mont->ri);
+
+	if (!BN_mul(t1,t2,&mont->N,ctx)) goto err;
+	if (!BN_add(t2,a,t1)) goto err;
+	if (!BN_rshift(ret,t2,mont->ri)) goto err;
+
+	if (BN_ucmp(ret, &(mont->N)) >= 0)
+		{
+		if (!BN_usub(ret,ret,&(mont->N))) goto err;
 		}
-#endif
+	retn=1;
+	bn_check_top(ret);
+ err:
+	BN_CTX_end(ctx);
+#endif /* MONT_WORD */
+	return(retn);
 	}
 
-BN_MONT_CTX *BN_MONT_CTX_new()
+BN_MONT_CTX *BN_MONT_CTX_new(void)
 	{
 	BN_MONT_CTX *ret;
 
-	if ((ret=(BN_MONT_CTX *)Malloc(sizeof(BN_MONT_CTX))) == NULL)
+	if ((ret=(BN_MONT_CTX *)OPENSSL_malloc(sizeof(BN_MONT_CTX))) == NULL)
 		return(NULL);
 
 	BN_MONT_CTX_init(ret);
@@ -281,10 +392,8 @@ BN_MONT_CTX *BN_MONT_CTX_new()
 	return(ret);
 	}
 
-void BN_MONT_CTX_init(ctx)
-BN_MONT_CTX *ctx;
+void BN_MONT_CTX_init(BN_MONT_CTX *ctx)
 	{
-	ctx->use_word=0;
 	ctx->ri=0;
 	BN_init(&(ctx->RR));
 	BN_init(&(ctx->N));
@@ -292,8 +401,7 @@ BN_MONT_CTX *ctx;
 	ctx->flags=0;
 	}
 
-void BN_MONT_CTX_free(mont)
-BN_MONT_CTX *mont;
+void BN_MONT_CTX_free(BN_MONT_CTX *mont)
 	{
 	if(mont == NULL)
 	    return;
@@ -302,117 +410,155 @@ BN_MONT_CTX *mont;
 	BN_free(&(mont->N));
 	BN_free(&(mont->Ni));
 	if (mont->flags & BN_FLG_MALLOCED)
-		Free(mont);
+		OPENSSL_free(mont);
 	}
 
-int BN_MONT_CTX_set(mont,mod,ctx)
-BN_MONT_CTX *mont;
-BIGNUM *mod;
-BN_CTX *ctx;
+int BN_MONT_CTX_set(BN_MONT_CTX *mont, const BIGNUM *mod, BN_CTX *ctx)
 	{
-	BIGNUM Ri,*R;
+	int ret = 0;
+	BIGNUM *Ri,*R;
 
-	BN_init(&Ri);
+	BN_CTX_start(ctx);
+	if((Ri = BN_CTX_get(ctx)) == NULL) goto err;
 	R= &(mont->RR);					/* grab RR as a temp */
-	BN_copy(&(mont->N),mod);			/* Set N */
+	if (!BN_copy(&(mont->N),mod)) goto err;		/* Set N */
+	mont->N.neg = 0;
 
-#ifdef BN_RECURSION
-	if (mont->N.top < BN_MONT_CTX_SET_SIZE_WORD)
-#endif
+#ifdef MONT_WORD
 		{
 		BIGNUM tmod;
 		BN_ULONG buf[2];
 
-		mont->use_word=1;
+		tmod.d=buf;
+		tmod.dmax=2;
+		tmod.neg=0;
 
 		mont->ri=(BN_num_bits(mod)+(BN_BITS2-1))/BN_BITS2*BN_BITS2;
+
+#if defined(OPENSSL_BN_ASM_MONT) && (BN_BITS2<=32)
 		BN_zero(R);
-		BN_set_bit(R,BN_BITS2);
-		/* I was bad, this modification of a passed variable was
-		 * breaking the multithreaded stuff :-(
-		 * z=mod->top;
-		 * mod->top=1; */
+		if (!(BN_set_bit(R,2*BN_BITS2))) goto err;
 
-		buf[0]=mod->d[0];
-		buf[1]=0;
-		tmod.d=buf;
-		tmod.top=1;
-		tmod.max=mod->max;
-		tmod.neg=mod->neg;
+								tmod.top=0;
+		if ((buf[0] = mod->d[0]))			tmod.top=1;
+		if ((buf[1] = mod->top>1 ? mod->d[1] : 0))	tmod.top=2;
 
-		if ((BN_mod_inverse(&Ri,R,&tmod,ctx)) == NULL)
+		if ((BN_mod_inverse(Ri,R,&tmod,ctx)) == NULL)
 			goto err;
-		BN_lshift(&Ri,&Ri,BN_BITS2);			/* R*Ri */
-		if (!BN_is_zero(&Ri))
+		if (!BN_lshift(Ri,Ri,2*BN_BITS2)) goto err; /* R*Ri */
+		if (!BN_is_zero(Ri))
 			{
-#if 1
-			BN_sub_word(&Ri,1);
+			if (!BN_sub_word(Ri,1)) goto err;
+			}
+		else /* if N mod word size == 1 */
+			{
+			if (bn_expand(Ri,(int)sizeof(BN_ULONG)*2) == NULL)
+				goto err;
+			/* Ri-- (mod double word size) */
+			Ri->neg=0;
+			Ri->d[0]=BN_MASK2;
+			Ri->d[1]=BN_MASK2;
+			Ri->top=2;
+			}
+		if (!BN_div(Ri,NULL,Ri,&tmod,ctx)) goto err;
+		/* Ni = (R*Ri-1)/N,
+		 * keep only couple of least significant words: */
+		mont->n0[0] = (Ri->top > 0) ? Ri->d[0] : 0;
+		mont->n0[1] = (Ri->top > 1) ? Ri->d[1] : 0;
 #else
-			BN_usub(&Ri,&Ri,BN_value_one());	/* R*Ri - 1 */
-#endif
+		BN_zero(R);
+		if (!(BN_set_bit(R,BN_BITS2))) goto err;	/* R */
+
+		buf[0]=mod->d[0]; /* tmod = N mod word size */
+		buf[1]=0;
+		tmod.top = buf[0] != 0 ? 1 : 0;
+							/* Ri = R^-1 mod N*/
+		if ((BN_mod_inverse(Ri,R,&tmod,ctx)) == NULL)
+			goto err;
+		if (!BN_lshift(Ri,Ri,BN_BITS2)) goto err; /* R*Ri */
+		if (!BN_is_zero(Ri))
+			{
+			if (!BN_sub_word(Ri,1)) goto err;
 			}
-		else
+		else /* if N mod word size == 1 */
 			{
-			/* This is not common..., 1 in BN_MASK2,
-			 * It happens when buf[0] was == 1.  So for 8 bit,
-			 * this is 1/256, 16bit, 1 in 2^16 etc.
-			 */
-			BN_set_word(&Ri,BN_MASK2);
+			if (!BN_set_word(Ri,BN_MASK2)) goto err;  /* Ri-- (mod word size) */
 			}
-		BN_div(&Ri,NULL,&Ri,&tmod,ctx);
-		mont->n0=Ri.d[0];
-		BN_free(&Ri);
-		/* mod->top=z; */
+		if (!BN_div(Ri,NULL,Ri,&tmod,ctx)) goto err;
+		/* Ni = (R*Ri-1)/N,
+		 * keep only least significant word: */
+		mont->n0[0] = (Ri->top > 0) ? Ri->d[0] : 0;
+		mont->n0[1] = 0;
+#endif
 		}
-#ifdef BN_RECURSION
-	else
-		{
-		mont->use_word=0;
-		mont->ri=(BN_num_bits(mod)+(BN_BITS2-1))/BN_BITS2*BN_BITS2;
-#if 1
+#else /* !MONT_WORD */
+		{ /* bignum version */
+		mont->ri=BN_num_bits(&mont->N);
 		BN_zero(R);
-		BN_set_bit(R,mont->ri);
-#else
-		BN_lshift(R,BN_value_one(),mont->ri);	/* R */
-#endif
-		if ((BN_mod_inverse(&Ri,R,mod,ctx)) == NULL)
+		if (!BN_set_bit(R,mont->ri)) goto err;  /* R = 2^ri */
+		                                        /* Ri = R^-1 mod N*/
+		if ((BN_mod_inverse(Ri,R,&mont->N,ctx)) == NULL)
 			goto err;
-		BN_lshift(&Ri,&Ri,mont->ri);		/* R*Ri */
-#if 1
-		BN_sub_word(&Ri,1);
-#else
-		BN_usub(&Ri,&Ri,BN_value_one());	/* R*Ri - 1 */
-#endif
-		BN_div(&(mont->Ni),NULL,&Ri,mod,ctx);
-		BN_free(&Ri);
+		if (!BN_lshift(Ri,Ri,mont->ri)) goto err; /* R*Ri */
+		if (!BN_sub_word(Ri,1)) goto err;
+							/* Ni = (R*Ri-1) / N */
+		if (!BN_div(&(mont->Ni),NULL,Ri,&mont->N,ctx)) goto err;
 		}
 #endif
 
 	/* setup RR for conversions */
-#if 1
 	BN_zero(&(mont->RR));
-	BN_set_bit(&(mont->RR),mont->ri*2);
-#else
-	BN_lshift(mont->RR,BN_value_one(),mont->ri*2);
-#endif
-	BN_mod(&(mont->RR),&(mont->RR),&(mont->N),ctx);
+	if (!BN_set_bit(&(mont->RR),mont->ri*2)) goto err;
+	if (!BN_mod(&(mont->RR),&(mont->RR),&(mont->N),ctx)) goto err;
 
-	return(1);
+	ret = 1;
 err:
-	return(0);
+	BN_CTX_end(ctx);
+	return ret;
 	}
 
-BN_MONT_CTX *BN_MONT_CTX_copy(to, from)
-BN_MONT_CTX *to, *from;
+BN_MONT_CTX *BN_MONT_CTX_copy(BN_MONT_CTX *to, BN_MONT_CTX *from)
 	{
 	if (to == from) return(to);
 
-	BN_copy(&(to->RR),&(from->RR));
-	BN_copy(&(to->N),&(from->N));
-	BN_copy(&(to->Ni),&(from->Ni));
-	to->use_word=from->use_word;
+	if (!BN_copy(&(to->RR),&(from->RR))) return NULL;
+	if (!BN_copy(&(to->N),&(from->N))) return NULL;
+	if (!BN_copy(&(to->Ni),&(from->Ni))) return NULL;
 	to->ri=from->ri;
-	to->n0=from->n0;
+	to->n0[0]=from->n0[0];
+	to->n0[1]=from->n0[1];
 	return(to);
 	}
 
+BN_MONT_CTX *BN_MONT_CTX_set_locked(BN_MONT_CTX **pmont, int lock,
+					const BIGNUM *mod, BN_CTX *ctx)
+	{
+	int got_write_lock = 0;
+	BN_MONT_CTX *ret;
+
+	CRYPTO_r_lock(lock);
+	if (!*pmont)
+		{
+		CRYPTO_r_unlock(lock);
+		CRYPTO_w_lock(lock);
+		got_write_lock = 1;
+
+		if (!*pmont)
+			{
+			ret = BN_MONT_CTX_new();
+			if (ret && !BN_MONT_CTX_set(ret, mod, ctx))
+				BN_MONT_CTX_free(ret);
+			else
+				*pmont = ret;
+			}
+		}
+	
+	ret = *pmont;
+	
+	if (got_write_lock)
+		CRYPTO_w_unlock(lock);
+	else
+		CRYPTO_r_unlock(lock);
+		
+	return ret;
+	}