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BN_div() cleanup: replace the use of BN_sub and BN_add with bn_sub_words

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and bn_add_words to avoid using fake bignums to window other bignums that
can lead to corruption. This change allows all bignum tests to pass with
BN_DEBUG and BN_DEBUG_RAND debugging and valgrind. NB: This should be
tested on a few different architectures and configuration targets, as the
bignum code this deals with is quite preprocessor (and assembly) sensitive.

Submitted by: Nils Narsch
Reviewed by: Geoff Thorpe, Ulf Moeller
This commit is contained in:
Geoff Thorpe 2003-11-22 20:23:41 +00:00
parent ec2179cf81
commit 9e989810ba
1 changed files with 45 additions and 36 deletions
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81
crypto/bn/bn_div.c
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@ -179,14 +179,16 @@ int BN_div(BIGNUM *dv, BIGNUM *rem, const BIGNUM *m, const BIGNUM *d,
int BN_div(BIGNUM *dv, BIGNUM *rm, const BIGNUM *num, const BIGNUM *divisor, int BN_div(BIGNUM *dv, BIGNUM *rm, const BIGNUM *num, const BIGNUM *divisor,
BN_CTX *ctx) BN_CTX *ctx)
{ {
int norm_shift,i,j,loop; int norm_shift,i,loop;
BIGNUM *tmp,wnum,*snum,*sdiv,*res; BIGNUM *tmp,wnum,*snum,*sdiv,*res;
BN_ULONG *resp,*wnump; BN_ULONG *resp,*wnump;
BN_ULONG d0,d1; BN_ULONG d0,d1;
int num_n,div_n; int num_n,div_n;
bn_check_top(dv); if (dv)
bn_check_top(rm); bn_check_top(dv);
if (rm)
bn_check_top(rm);
bn_check_top(num); bn_check_top(num);
bn_check_top(divisor); bn_check_top(divisor);
@ -224,15 +226,16 @@ int BN_div(BIGNUM *dv, BIGNUM *rm, const BIGNUM *num, const BIGNUM *divisor,
div_n=sdiv->top; div_n=sdiv->top;
num_n=snum->top; num_n=snum->top;
loop=num_n-div_n; loop=num_n-div_n;
/* Lets setup a 'window' into snum /* Lets setup a 'window' into snum
* This is the part that corresponds to the current * This is the part that corresponds to the current
* 'area' being divided */ * 'area' being divided */
BN_init(&wnum); wnum.neg = 0;
wnum.flags = BN_FLG_STATIC_DATA; /* prevent accidental "expands" */ wnum.d = &(snum->d[loop]);
wnum.d= &(snum->d[loop]); wnum.top = div_n;
wnum.top= div_n; #ifdef BN_DEBUG_RAND
wnum.dmax= snum->dmax - loop; /* so we don't step out of bounds */ /* 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 */
#endif
/* Get the top 2 words of sdiv */ /* Get the top 2 words of sdiv */
/* div_n=sdiv->top; */ /* div_n=sdiv->top; */
@ -251,22 +254,32 @@ int BN_div(BIGNUM *dv, BIGNUM *rm, const BIGNUM *num, const BIGNUM *divisor,
/* space for temp */ /* space for temp */
if (!bn_wexpand(tmp,(div_n+1))) goto err; if (!bn_wexpand(tmp,(div_n+1))) goto err;
bn_correct_top(&wnum);
if (BN_ucmp(&wnum,sdiv) >= 0) if (BN_ucmp(&wnum,sdiv) >= 0)
{ {
if (!BN_usub(&wnum,&wnum,sdiv)) goto err; #ifdef BN_DEBUG_RAND
/* 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);
#endif
bn_sub_words(wnum.d, wnum.d, sdiv->d, div_n);
*resp=1; *resp=1;
res->d[res->top-1]=1;
} }
else else
res->top--; res->top--;
/* if res->top == 0 then clear the neg value otherwise decrease
* the resp pointer */
if (res->top == 0) if (res->top == 0)
res->neg = 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; 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) #if defined(BN_DIV3W) && !defined(OPENSSL_NO_ASM)
BN_ULONG bn_div_3_words(BN_ULONG*,BN_ULONG,BN_ULONG); BN_ULONG bn_div_3_words(BN_ULONG*,BN_ULONG,BN_ULONG);
q=bn_div_3_words(wnump,d1,d0); q=bn_div_3_words(wnump,d1,d0);
@ -350,31 +363,26 @@ X) -> 0x%08X\n",
#endif /* !BN_DIV3W */ #endif /* !BN_DIV3W */
l0=bn_mul_words(tmp->d,sdiv->d,div_n,q); l0=bn_mul_words(tmp->d,sdiv->d,div_n,q);
wnum.d--; wnum.top++; wnum.dmax++;
tmp->d[div_n]=l0; tmp->d[div_n]=l0;
/* XXX: Couldn't we replace this with; wnum.d--;
* tmp->top = div_n; /* ingore top values of the bignums just sub the two
* bn_fix_top(tmp); * BN_ULONG arrays with bn_sub_words */
*/ if (bn_sub_words(wnum.d, wnum.d, tmp->d, div_n+1))
for (j=div_n+1; j>0; j--)
if (tmp->d[j-1]) break;
tmp->top=j;
j=wnum.top;
bn_correct_top(&wnum);
if (!BN_sub(&wnum,&wnum,tmp)) goto err;
snum->top=snum->top+wnum.top-j;
if (wnum.neg)
{ {
/* 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--; q--;
j=wnum.top; if (bn_add_words(wnum.d, wnum.d, sdiv->d, div_n))
if (!BN_add(&wnum,&wnum,sdiv)) goto err; /* we can't have an overflow here (assuming
snum->top+=wnum.top-j; * that q != 0, but if q == 0 then tmp is
* zero anyway) */
(*wnump)++;
} }
*(resp--)=q; /* store part of the result */
wnump--; *resp = q;
} }
if (rm != NULL) if (rm != NULL)
{ {
@ -391,7 +399,8 @@ X) -> 0x%08X\n",
BN_CTX_end(ctx); BN_CTX_end(ctx);
return(1); return(1);
err: err:
bn_check_top(rm); if (rm)
bn_check_top(rm);
BN_CTX_end(ctx); BN_CTX_end(ctx);
return(0); return(0);
} }