From bf3dfe7feee5f62ba1e4367720819255db039f29 Mon Sep 17 00:00:00 2001 From: Andy Polyakov Date: Sun, 14 Aug 2011 11:31:35 +0000 Subject: [PATCH] bn_div.c: remove duplicate code by merging BN_div and BN_div_no_branch. --- crypto/bn/bn_div.c | 272 ++++++--------------------------------------- 1 file changed, 34 insertions(+), 238 deletions(-) diff --git a/crypto/bn/bn_div.c b/crypto/bn/bn_div.c index 92ef8cb918..034a80a4a6 100644 --- a/crypto/bn/bn_div.c +++ b/crypto/bn/bn_div.c @@ -173,15 +173,13 @@ int BN_div(BIGNUM *dv, BIGNUM *rem, const BIGNUM *m, const BIGNUM *d, #endif /* OPENSSL_NO_ASM */ -/* BN_div[_no_branch] computes dv := num / divisor, rounding towards +/* BN_div 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) { @@ -190,6 +188,7 @@ int BN_div(BIGNUM *dv, BIGNUM *rm, const BIGNUM *num, const BIGNUM *divisor, BN_ULONG *resp,*wnump; BN_ULONG d0,d1; int num_n,div_n; + int no_branch=0; /* Invalid zero-padding would have particularly bad consequences * in the case of 'num', so don't just rely on bn_check_top() for this one @@ -204,7 +203,7 @@ int BN_div(BIGNUM *dv, BIGNUM *rm, const BIGNUM *num, const BIGNUM *divisor, 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); + no_branch=1; } bn_check_top(dv); @@ -218,7 +217,7 @@ int BN_div(BIGNUM *dv, BIGNUM *rm, const BIGNUM *num, const BIGNUM *divisor, return(0); } - if (BN_ucmp(num,divisor) < 0) + if (!no_branch && BN_ucmp(num,divisor) < 0) { if (rm != NULL) { if (BN_copy(rm,num) == NULL) return(0); } @@ -243,242 +242,25 @@ int BN_div(BIGNUM *dv, BIGNUM *rm, const BIGNUM *num, const BIGNUM *divisor, norm_shift+=BN_BITS2; if (!(BN_lshift(snum,num,norm_shift))) goto err; snum->neg=0; - 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; - resp= &(res->d[loop-1]); - - /* space for temp */ - if (!bn_wexpand(tmp,(div_n+1))) goto err; - if (BN_ucmp(&wnum,sdiv) >= 0) + if (no_branch) { - /* 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; - } - else - res->top--; - /* 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 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)< 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 + /* 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) { - BN_ULONG ql, qh; - t2l=LBITS(d1); t2h=HBITS(d1); - ql =LBITS(q); qh =HBITS(q); - mul64(t2l,t2h,ql,qh); /* t2=(BN_ULLONG)d1*q; */ + 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; } -#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)) + else { - /* 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)++; + if (bn_wexpand(snum, snum->top + 1) == NULL) goto err; + snum->d[snum->top] = 0; + snum->top ++; } - /* 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); */ /* 'num' has been checked in BN_div() */ - 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; @@ -504,12 +286,27 @@ static int BN_div_no_branch(BIGNUM *dv, BIGNUM *rm, const BIGNUM *num, /* Setup to 'res' */ res->neg= (num->neg^divisor->neg); if (!bn_wexpand(res,(loop+1))) goto err; - res->top=loop-1; + res->top=loop-no_branch; resp= &(res->d[loop-1]); /* space for temp */ if (!bn_wexpand(tmp,(div_n+1))) goto err; + if (!no_branch) + { + if (BN_ucmp(&wnum,sdiv) >= 0) + { + /* 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; + } + else + res->top--; + } + /* if res->top == 0 then clear the neg value otherwise decrease * the resp pointer */ if (res->top == 0) @@ -642,7 +439,7 @@ X) -> 0x%08X\n", rm->neg = neg; bn_check_top(rm); } - bn_correct_top(res); + if (no_branch) bn_correct_top(res); BN_CTX_end(ctx); return(1); err: @@ -650,5 +447,4 @@ err: BN_CTX_end(ctx); return(0); } - #endif -- 2.25.1