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Enhancement to RSA math function "_fp_exptmod" (non timing resistant version) to support WOLFSSL_SMALL_STACK, which moves the allocation of the 64 fp_int's from the stack to the heap.

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This commit is contained in:
David Garske
2016-05-04 23:20:55 -07:00
parent fa5dd01001
commit 0ddbe0e60e
1 changed files with 25 additions and 7 deletions
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32
wolfcrypt/src/tfm.c
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@ -1059,9 +1059,14 @@ static int _fp_exptmod(fp_int * G, fp_int * X, fp_int * P, fp_int * Y)
*/
static int _fp_exptmod(fp_int * G, fp_int * X, fp_int * P, fp_int * Y)
{
fp_int M[64], res;
fp_int res;
fp_digit buf, mp;
int err, bitbuf, bitcpy, bitcnt, mode, digidx, x, y, winsize;
#ifdef WOLFSSL_SMALL_STACK
fp_int *M;
#else
fp_int M[64];
#endif
/* find window size */
x = fp_count_bits (X);
@ -1077,15 +1082,23 @@ static int _fp_exptmod(fp_int * G, fp_int * X, fp_int * P, fp_int * Y)
winsize = 6;
}
/* init M array */
for(x = 0; x < (int)(sizeof(M)/sizeof(fp_int)); x++)
fp_init(&M[x]);
/* now setup montgomery */
if ((err = fp_montgomery_setup (P, &mp)) != FP_OKAY) {
return err;
}
#ifdef WOLFSSL_SMALL_STACK
/* only allocate space for what's needed */
M = (fp_int*)XMALLOC(sizeof(fp_int)*(1 << winsize), NULL, DYNAMIC_TYPE_TMP_BUFFER);
if (M == NULL) {
return FP_MEM;
}
#endif
/* init M array */
for(x = 0; x < (1 << winsize); x++)
fp_init(&M[x]);
/* setup result */
fp_init(&res);
@ -1093,7 +1106,7 @@ static int _fp_exptmod(fp_int * G, fp_int * X, fp_int * P, fp_int * Y)
*
* The M table contains powers of the input base, e.g. M[x] = G^x mod P
*
* The first half of the table is not computed though accept for M[0] and M[1]
* The first half of the table is not computed though except for M[0] and M[1]
*/
/* now we need R mod m */
@ -1212,10 +1225,15 @@ static int _fp_exptmod(fp_int * G, fp_int * X, fp_int * P, fp_int * Y)
/* swap res with Y */
fp_copy (&res, Y);
#ifdef WOLFSSL_SMALL_STACK
XFREE(M, NULL, DYNAMIC_TYPE_TMP_BUFFER);
#endif
return FP_OKAY;
}
#endif
#endif /* TFM_TIMING_RESISTANT */
int fp_exptmod(fp_int * G, fp_int * X, fp_int * P, fp_int * Y)
{