diff options
Diffstat (limited to 'crypto/bn/bn_div.c')
| -rw-r--r-- | crypto/bn/bn_div.c | 265 |
1 files changed, 256 insertions, 9 deletions
diff --git a/crypto/bn/bn_div.c b/crypto/bn/bn_div.c index 3b4392955e..899d07ca24 100644 --- a/crypto/bn/bn_div.c +++ b/crypto/bn/bn_div.c @@ -169,13 +169,15 @@ 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) { @@ -185,11 +187,25 @@ 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); + /* 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 + * (bn_check_top() works only for BN_DEBUG builds) */ + if (num->top > 0 && num->d[num->top - 1] == 0) + { + BNerr(BN_F_BN_DIV,BN_R_NOT_INITIALIZED); + return 0; + } + bn_check_top(num); + + 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); */ /* 'num' has been checked already */ bn_check_top(divisor); if (BN_is_zero(divisor)) @@ -213,7 +229,8 @@ int BN_div(BIGNUM *dv, BIGNUM *rm, const BIGNUM *num, const BIGNUM *divisor, if (dv == NULL) res=BN_CTX_get(ctx); else res=dv; - if (sdiv == NULL || res == NULL) goto err; + if (sdiv == NULL || res == NULL || tmp == NULL || snum == NULL) + goto err; /* First we normalise the numbers */ norm_shift=BN_BITS2-((BN_num_bits(divisor))%BN_BITS2); @@ -320,7 +337,7 @@ X) -> 0x%08X\n", t2 -= d1; } #else /* !BN_LLONG */ - BN_ULONG t2l,t2h,ql,qh; + BN_ULONG t2l,t2h; q=bn_div_words(n0,n1,d0); #ifdef BN_DEBUG_LEVITTE @@ -338,9 +355,12 @@ X) -> 0x%08X\n", t2l = d1 * q; t2h = BN_UMULT_HIGH(d1,q); #else + { + 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; */ + } #endif for (;;) @@ -394,8 +414,235 @@ 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. + */ +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; + 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; + + 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 + { + 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; */ + } +#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); } |