X-Git-Url: https://git.openssl.org/?p=openssl.git;a=blobdiff_plain;f=crypto%2Fbn%2Fbn_div.c;h=257fe0ce01b2f19fdfb10062be775fa852fd9dc1;hp=556fcda1e3686d88745550a8099b501ed81be154;hb=d1e7d1d96cbec34a44449e19433b5fe7d748e06a;hpb=a8aa764d3c96eb65b22863cdc5f6ab08d92dd355

diff --git a/crypto/bn/bn_div.c b/crypto/bn/bn_div.c
index 556fcda1e3..257fe0ce01 100644
--- a/crypto/bn/bn_div.c
+++ b/crypto/bn/bn_div.c
@@ -185,10 +185,13 @@ int BN_div(BIGNUM *dv, BIGNUM *rm, const BIGNUM *num, const BIGNUM *divisor,
 	BN_ULONG d0,d1;
 	int num_n,div_n;
 
-	if (dv)
-		bn_check_top(dv);
-	if (rm)
-		bn_check_top(rm);
+	if ((BN_get_flags(num, BN_FLG_CONSTTIME) != 0) || (BN_get_flags(divisor, BN_FLG_CONSTTIME) != 0))
+		{
+		return BN_div_no_branch(dv, rm, num, divisor, ctx);
+		}
+
+	bn_check_top(dv);
+	bn_check_top(rm);
 	bn_check_top(num);
 	bn_check_top(divisor);
 
@@ -214,7 +217,6 @@ int BN_div(BIGNUM *dv, BIGNUM *rm, const BIGNUM *num, const BIGNUM *divisor,
 		res=BN_CTX_get(ctx);
 	else	res=dv;
 	if (sdiv == NULL || res == NULL) goto err;
-	tmp->neg=0;
 
 	/* First we normalise the numbers */
 	norm_shift=BN_BITS2-((BN_num_bits(divisor))%BN_BITS2);
@@ -395,8 +397,232 @@ X) -> 0x%08X\n",
 	BN_CTX_end(ctx);
 	return(1);
 err:
-	if (rm)
+	bn_check_top(rm);
+	BN_CTX_end(ctx);
+	return(0);
+	}
+
+
+/* BN_div_no_branch is a special version of BN_div. It does not contain
+ * branches that may leak sensitive information.
+ */
+int BN_div_no_branch(BIGNUM *dv, BIGNUM *rm, const BIGNUM *num, 
+	const BIGNUM *divisor, BN_CTX *ctx)
+	{
+	int norm_shift,i,loop;
+	BIGNUM *tmp,wnum,*snum,*sdiv,*res;
+	BN_ULONG *resp,*wnump;
+	BN_ULONG d0,d1;
+	int num_n,div_n;
+
+	bn_check_top(dv);
+	bn_check_top(rm);
+	bn_check_top(num);
+	bn_check_top(divisor);
+
+	if (BN_is_zero(divisor))
+		{
+		BNerr(BN_F_BN_DIV,BN_R_DIV_BY_ZERO);
+		return(0);
+		}
+
+	BN_CTX_start(ctx);
+	tmp=BN_CTX_get(ctx);
+	snum=BN_CTX_get(ctx);
+	sdiv=BN_CTX_get(ctx);
+	if (dv == NULL)
+		res=BN_CTX_get(ctx);
+	else	res=dv;
+	if (sdiv == NULL || res == NULL) goto err;
+
+	/* First we normalise the numbers */
+	norm_shift=BN_BITS2-((BN_num_bits(divisor))%BN_BITS2);
+	if (!(BN_lshift(sdiv,divisor,norm_shift))) goto err;
+	sdiv->neg=0;
+	norm_shift+=BN_BITS2;
+	if (!(BN_lshift(snum,num,norm_shift))) goto err;
+	snum->neg=0;
+
+	/* Since we don't know whether snum is larger than sdiv,
+	 * we pad snum with enough zeroes without changing its
+	 * value. 
+	 */
+	if (snum->top <= sdiv->top+1) 
+		{
+		if (bn_wexpand(snum, sdiv->top + 2) == NULL) goto err;
+		for (i = snum->top; i < sdiv->top + 2; i++) snum->d[i] = 0;
+		snum->top = sdiv->top + 2;
+		}
+	else
+		{
+		if (bn_wexpand(snum, snum->top + 1) == NULL) goto err;
+		snum->d[snum->top] = 0;
+		snum->top ++;
+		}
+
+	div_n=sdiv->top;
+	num_n=snum->top;
+	loop=num_n-div_n;
+	/* Lets setup a 'window' into snum
+	 * This is the part that corresponds to the current
+	 * 'area' being divided */
+	wnum.neg   = 0;
+	wnum.d     = &(snum->d[loop]);
+	wnum.top   = div_n;
+	/* only needed when BN_ucmp messes up the values between top and max */
+	wnum.dmax  = snum->dmax - loop; /* so we don't step out of bounds */
+
+	/* Get the top 2 words of sdiv */
+	/* div_n=sdiv->top; */
+	d0=sdiv->d[div_n-1];
+	d1=(div_n == 1)?0:sdiv->d[div_n-2];
+
+	/* pointer to the 'top' of snum */
+	wnump= &(snum->d[num_n-1]);
+
+	/* Setup to 'res' */
+	res->neg= (num->neg^divisor->neg);
+	if (!bn_wexpand(res,(loop+1))) goto err;
+	res->top=loop-1;
+	resp= &(res->d[loop-1]);
+
+	/* space for temp */
+	if (!bn_wexpand(tmp,(div_n+1))) goto err;
+
+	/* if res->top == 0 then clear the neg value otherwise decrease
+	 * the resp pointer */
+	if (res->top == 0)
+		res->neg = 0;
+	else
+		resp--;
+
+	for (i=0; i<loop-1; i++, wnump--, resp--)
+		{
+		BN_ULONG q,l0;
+		/* the first part of the loop uses the top two words of
+		 * snum and sdiv to calculate a BN_ULONG q such that
+		 * | wnum - sdiv * q | < sdiv */
+#if defined(BN_DIV3W) && !defined(OPENSSL_NO_ASM)
+		BN_ULONG bn_div_3_words(BN_ULONG*,BN_ULONG,BN_ULONG);
+		q=bn_div_3_words(wnump,d1,d0);
+#else
+		BN_ULONG n0,n1,rem=0;
+
+		n0=wnump[0];
+		n1=wnump[-1];
+		if (n0 == d0)
+			q=BN_MASK2;
+		else 			/* n0 < d0 */
+			{
+#ifdef BN_LLONG
+			BN_ULLONG t2;
+
+#if defined(BN_LLONG) && defined(BN_DIV2W) && !defined(bn_div_words)
+			q=(BN_ULONG)(((((BN_ULLONG)n0)<<BN_BITS2)|n1)/d0);
+#else
+			q=bn_div_words(n0,n1,d0);
+#ifdef BN_DEBUG_LEVITTE
+			fprintf(stderr,"DEBUG: bn_div_words(0x%08X,0x%08X,0x%08\
+X) -> 0x%08X\n",
+				n0, n1, d0, q);
+#endif
+#endif
+
+#ifndef REMAINDER_IS_ALREADY_CALCULATED
+			/*
+			 * rem doesn't have to be BN_ULLONG. The least we
+			 * know it's less that d0, isn't it?
+			 */
+			rem=(n1-q*d0)&BN_MASK2;
+#endif
+			t2=(BN_ULLONG)d1*q;
+
+			for (;;)
+				{
+				if (t2 <= ((((BN_ULLONG)rem)<<BN_BITS2)|wnump[-2]))
+					break;
+				q--;
+				rem += d0;
+				if (rem < d0) break; /* don't let rem overflow */
+				t2 -= d1;
+				}
+#else /* !BN_LLONG */
+			BN_ULONG t2l,t2h,ql,qh;
+
+			q=bn_div_words(n0,n1,d0);
+#ifdef BN_DEBUG_LEVITTE
+			fprintf(stderr,"DEBUG: bn_div_words(0x%08X,0x%08X,0x%08\
+X) -> 0x%08X\n",
+				n0, n1, d0, q);
+#endif
+#ifndef REMAINDER_IS_ALREADY_CALCULATED
+			rem=(n1-q*d0)&BN_MASK2;
+#endif
+
+#if defined(BN_UMULT_LOHI)
+			BN_UMULT_LOHI(t2l,t2h,d1,q);
+#elif defined(BN_UMULT_HIGH)
+			t2l = d1 * q;
+			t2h = BN_UMULT_HIGH(d1,q);
+#else
+			t2l=LBITS(d1); t2h=HBITS(d1);
+			ql =LBITS(q);  qh =HBITS(q);
+			mul64(t2l,t2h,ql,qh); /* t2=(BN_ULLONG)d1*q; */
+#endif
+
+			for (;;)
+				{
+				if ((t2h < rem) ||
+					((t2h == rem) && (t2l <= wnump[-2])))
+					break;
+				q--;
+				rem += d0;
+				if (rem < d0) break; /* don't let rem overflow */
+				if (t2l < d1) t2h--; t2l -= d1;
+				}
+#endif /* !BN_LLONG */
+			}
+#endif /* !BN_DIV3W */
+
+		l0=bn_mul_words(tmp->d,sdiv->d,div_n,q);
+		tmp->d[div_n]=l0;
+		wnum.d--;
+		/* ingore top values of the bignums just sub the two 
+		 * BN_ULONG arrays with bn_sub_words */
+		if (bn_sub_words(wnum.d, wnum.d, tmp->d, div_n+1))
+			{
+			/* Note: As we have considered only the leading
+			 * two BN_ULONGs in the calculation of q, sdiv * q
+			 * might be greater than wnum (but then (q-1) * sdiv
+			 * is less or equal than wnum)
+			 */
+			q--;
+			if (bn_add_words(wnum.d, wnum.d, sdiv->d, div_n))
+				/* we can't have an overflow here (assuming
+				 * that q != 0, but if q == 0 then tmp is
+				 * zero anyway) */
+				(*wnump)++;
+			}
+		/* store part of the result */
+		*resp = q;
+		}
+	bn_correct_top(snum);
+	if (rm != NULL)
+		{
+		/* Keep a copy of the neg flag in num because if rm==num
+		 * BN_rshift() will overwrite it.
+		 */
+		int neg = num->neg;
+		BN_rshift(rm,snum,norm_shift);
+		if (!BN_is_zero(rm))
+			rm->neg = neg;
 		bn_check_top(rm);
+		}
+	bn_correct_top(res);
+	BN_CTX_end(ctx);
+	return(1);
+err:
+	bn_check_top(rm);
 	BN_CTX_end(ctx);
 	return(0);
 	}