1 files changed, 272 insertions, 27 deletions

diff --git a/src/lib/libcrypto/bn/bn_div.c b/src/lib/libcrypto/bn/bn_div.c
index 580d1201bc..8655eb118e 100644
--- a/src/lib/libcrypto/bn/bn_div.c
+++ b/src/lib/libcrypto/bn/bn_div.c
@@ -169,22 +169,31 @@ int BN_div(BIGNUM *dv, BIGNUM *rem, const BIGNUM *m, const BIGNUM *d,
 #endif /* OPENSSL_NO_ASM */
 
 
-/* BN_div computes  dv := num / divisor,  rounding towards zero, and sets up
- * rm  such that  dv*divisor + rm = num  holds.
+/* BN_div[_no_branch] computes  dv := num / divisor,  rounding towards
+ * zero, and sets up rm  such that  dv*divisor + rm = num  holds.
  * Thus:
  *     dv->neg == num->neg ^ divisor->neg  (unless the result is zero)
  *     rm->neg == num->neg                 (unless the remainder is zero)
  * If 'dv' or 'rm' is NULL, the respective value is not returned.
  */
+static int BN_div_no_branch(BIGNUM *dv, BIGNUM *rm, const BIGNUM *num,
+        const BIGNUM *divisor, BN_CTX *ctx);
 int BN_div(BIGNUM *dv, BIGNUM *rm, const BIGNUM *num, const BIGNUM *divisor,
            BN_CTX *ctx)
         {
-        int norm_shift,i,j,loop;
+        int norm_shift,i,loop;
         BIGNUM *tmp,wnum,*snum,*sdiv,*res;
         BN_ULONG *resp,*wnump;
         BN_ULONG d0,d1;
         int num_n,div_n;
 
+        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);
 
@@ -210,7 +219,6 @@ 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);
@@ -222,17 +230,17 @@ int BN_div(BIGNUM *dv, BIGNUM *rm, const BIGNUM *num, const BIGNUM *divisor,
         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 */
-        BN_init(&wnum);
-        wnum.d=  &(snum->d[loop]);
-        wnum.top= div_n;
-        wnum.dmax= snum->dmax+1; /* a bit of a lie */
+        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 */
-        /* i=sdiv->top; */
+        /* div_n=sdiv->top; */
         d0=sdiv->d[div_n-1];
         d1=(div_n == 1)?0:sdiv->d[div_n-2];
 
@@ -250,19 +258,28 @@ int BN_div(BIGNUM *dv, BIGNUM *rm, const BIGNUM *num, const BIGNUM *divisor,
 
         if (BN_ucmp(&wnum,sdiv) >= 0)
                 {
-                if (!BN_usub(&wnum,&wnum,sdiv)) goto err;
+                /* If BN_DEBUG_RAND is defined BN_ucmp changes (via
+                 * bn_pollute) the const bignum arguments =>
+                 * clean the values between top and max again */
+                bn_clear_top2max(&wnum);
+                bn_sub_words(wnum.d, wnum.d, sdiv->d, div_n);
                 *resp=1;
-                res->d[res->top-1]=1;
                 }
         else
                 res->top--;
+        /* if res->top == 0 then clear the neg value otherwise decrease
+         * the resp pointer */
         if (res->top == 0)
                 res->neg = 0;
-        resp--;
+        else
+                resp--;
 
-        for (i=0; i<loop-1; i++)
+        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);
@@ -346,27 +363,252 @@ X) -> 0x%08X\n",
 #endif /* !BN_DIV3W */
 
                 l0=bn_mul_words(tmp->d,sdiv->d,div_n,q);
-                wnum.d--; wnum.top++;
                 tmp->d[div_n]=l0;
-                for (j=div_n+1; j>0; j--)
-                        if (tmp->d[j-1]) break;
-                tmp->top=j;
+                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_CTX_end(ctx);
+        return(1);
+err:
+        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.
+ */
+static 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_NO_BRANCH,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
 
-                j=wnum.top;
-                if (!BN_sub(&wnum,&wnum,tmp)) goto err;
+#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
 
-                snum->top=snum->top+wnum.top-j;
+                        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 */
 
-                if (wnum.neg)
+                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--;
-                        j=wnum.top;
-                        if (!BN_add(&wnum,&wnum,sdiv)) goto err;
-                        snum->top+=wnum.top-j;
+                        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)++;
                         }
-                *(resp--)=q;
-                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
@@ -376,10 +618,13 @@ X) -> 0x%08X\n",
                 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);
         }