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mp_sqrtmod_prime: bail early on the check for small values

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When using custom curves, only use the first 22 values with the prime to
calculate Legendre symbol. The known curves work and defeats long running
times when non-prime values are passed in.
This commit is contained in:
Sean Parkinson 2023-10-03 08:44:28 +10:00
parent ecf666a121
commit e55e6790dd
1 changed files with 43 additions and 4 deletions
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47
wolfcrypt/src/ecc.c
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@ -1346,7 +1346,9 @@ static int _ecc_pairwise_consistency_test(ecc_key* key, WC_RNG* rng);
!defined(WOLFSSL_CRYPTOCELL)
#ifndef WOLFSSL_SP_MATH
#if !defined(SQRTMOD_USE_MOD_EXP)
static int mp_jacobi(mp_int* a, mp_int* n, int* c);
#endif
static int mp_sqrtmod_prime(mp_int* n, mp_int* prime, mp_int* ret);
#endif
#endif
@ -14480,6 +14482,7 @@ int wc_ecc_decrypt(ecc_key* privKey, ecc_key* pubKey, const byte* msg,
!defined(WOLFSSL_CRYPTOCELL)
#ifndef WOLFSSL_SP_MATH
#if !defined(SQRTMOD_USE_MOD_EXP)
/* computes the jacobi c = (a | n) (or Legendre if n is prime)
*/
static int mp_jacobi(mp_int* a, mp_int* n, int* c)
@ -14599,6 +14602,7 @@ done:
return res;
}
#endif /* !SQRTMOD_USE_MOD_EXP */
/* Solves the modular equation x^2 = n (mod p)
@ -14608,18 +14612,44 @@ done:
*/
static int mp_sqrtmod_prime(mp_int* n, mp_int* prime, mp_int* ret)
{
#ifdef SQRTMOD_USE_MOD_EXP
#if defined(SQRTMOD_USE_MOD_EXP)
int res;
mp_digit i;
mp_int e;
/* first handle the simple cases n = 0 or n = 1 */
if (mp_cmp_d(n, 0) == MP_EQ) {
mp_zero(ret);
return MP_OKAY;
}
if (mp_cmp_d(n, 1) == MP_EQ) {
return mp_set(ret, 1);
}
if (mp_iseven(prime)) {
return MP_VAL;
}
SAVE_VECTOR_REGISTERS(return _svr_ret;);
res = mp_init(&e);
if (res == MP_OKAY)
res = mp_mod_d(prime, 8, &i);
if (res == MP_OKAY && i == 1) {
return MP_VAL;
}
/* prime mod 8 = 5 */
else if (res == MP_OKAY && i == 5) {
res = mp_sub_d(prime, 1, &e);
if (res == MP_OKAY)
res = mp_div_2d(&e, 2, &e, NULL);
}
/* prime mod 4 = 3 */
else if (res == MP_OKAY && ((i == 3) || (i == 7))) {
res = mp_add_d(prime, 1, &e);
if (res == MP_OKAY)
res = mp_div_2d(&e, 2, &e, NULL);
if (res == MP_OKAY)
res = mp_div_2d(&e, 2, &e, NULL);
}
if (res == MP_OKAY)
res = mp_exptmod(n, &e, prime, ret);
@ -14758,6 +14788,15 @@ static int mp_sqrtmod_prime(mp_int* n, mp_int* prime, mp_int* ret)
if (res == MP_OKAY && legendre == -1)
break;
#if defined(WOLFSSL_CUSTOM_CURVES)
/* P224R1 succeeds with a value of 11. */
if (mp_cmp_d(Z, 22) == MP_EQ) {
/* This is to clamp the loop in case 'prime' is not really prime */
res = MP_VAL;
break;
}
#endif
/* Z = Z + 1 */
if (res == MP_OKAY)
res = mp_add_d(Z, 1, Z);