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Improve nonce use in ECC mulmod #2353

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merged 1 commit into from Jul 17, 2019
Merged

Improve nonce use in ECC mulmod #2353

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64 changes: 47 additions & 17 deletions wolfcrypt/src/ecc.c
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Expand Up @@ -2479,7 +2479,7 @@ int wc_ecc_mulmod_ex(mp_int* k, ecc_point *G, ecc_point *R,
#define M_POINTS 8
int first = 1, bitbuf = 0, bitcpy = 0, j;
#else
#define M_POINTS 3
#define M_POINTS 4
#endif

ecc_point *tG, *M[M_POINTS];
Expand Down Expand Up @@ -2771,7 +2771,9 @@ int wc_ecc_mulmod_ex(mp_int* k, ecc_point *G, ecc_point *R,
mode = 0;
bitcnt = 1;
buf = 0;
digidx = get_digit_count(k) - 1;
digidx = get_digit_count(modulus) - 1;
/* The order MAY be 1 bit longer than the modulus. */
digidx += (modulus->dp[digidx] >> (DIGIT_BIT-1));

/* perform ops */
if (err == MP_OKAY) {
Expand All @@ -2790,25 +2792,53 @@ int wc_ecc_mulmod_ex(mp_int* k, ecc_point *G, ecc_point *R,
i = (buf >> (DIGIT_BIT - 1)) & 1;
buf <<= 1;

if (mode == 0 && i == 0) {
if (mode == 0) {
mode = i;
/* timing resistant - dummy operations */
if (err == MP_OKAY)
err = ecc_projective_add_point(M[0], M[1], M[2], a, modulus,
mp);
if (err == MP_OKAY)
err = ecc_projective_dbl_point(M[1], M[2], a, modulus, mp);
if (err == MP_OKAY)
continue;
}

if (mode == 0 && i == 1) {
mode = 1;
/* timing resistant - dummy operations */
if (err == MP_OKAY)
err = ecc_projective_add_point(M[0], M[1], M[2], a, modulus,
err = ecc_projective_add_point(M[1], M[2], M[2], a, modulus,
mp);
#ifdef WC_NO_CACHE_RESISTANT
if (err == MP_OKAY)
err = ecc_projective_dbl_point(M[1], M[2], a, modulus, mp);
err = ecc_projective_dbl_point(M[2], M[3], a, modulus, mp);
#else
/* instead of using M[i] for double, which leaks key bit to cache
* monitor, use M[2] as temp, make sure address calc is constant,
* keep M[0] and M[1] in cache */
if (err == MP_OKAY)
err = mp_copy((mp_int*)
( ((wolfssl_word)M[0]->x & wc_off_on_addr[i^1]) +
((wolfssl_word)M[1]->x & wc_off_on_addr[i])),
M[2]->x);
if (err == MP_OKAY)
err = mp_copy((mp_int*)
( ((wolfssl_word)M[0]->y & wc_off_on_addr[i^1]) +
((wolfssl_word)M[1]->y & wc_off_on_addr[i])),
M[2]->y);
if (err == MP_OKAY)
err = mp_copy((mp_int*)
( ((wolfssl_word)M[0]->z & wc_off_on_addr[i^1]) +
((wolfssl_word)M[1]->z & wc_off_on_addr[i])),
M[2]->z);
if (err == MP_OKAY)
err = ecc_projective_dbl_point(M[2], M[3], a, modulus, mp);
/* copy M[2] back to M[i] */
if (err == MP_OKAY)
err = mp_copy(M[2]->x,
(mp_int*)
( ((wolfssl_word)M[0]->x & wc_off_on_addr[i^1]) +
((wolfssl_word)M[1]->x & wc_off_on_addr[i])) );
if (err == MP_OKAY)
err = mp_copy(M[2]->y,
(mp_int*)
( ((wolfssl_word)M[0]->y & wc_off_on_addr[i^1]) +
((wolfssl_word)M[1]->y & wc_off_on_addr[i])) );
if (err == MP_OKAY)
err = mp_copy(M[2]->z,
(mp_int*)
( ((wolfssl_word)M[0]->z & wc_off_on_addr[i^1]) +
((wolfssl_word)M[1]->z & wc_off_on_addr[i])) );
#endif
if (err == MP_OKAY)
continue;
}
Expand Down