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RSA private exponentiation: multiply blinding invert in Mont #6955

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Nov 28, 2023
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RSA private exponentiation: multiply blinding invert in Mont #6955

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33 changes: 29 additions & 4 deletions wolfcrypt/src/rsa.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2495,6 +2495,7 @@ static int RsaFunctionPrivate(mp_int* tmp, RsaKey* key, WC_RNG* rng)
{
int ret = 0;
#if defined(WC_RSA_BLINDING) && !defined(WC_NO_RNG)
mp_digit mp;
DECL_MP_INT_SIZE_DYN(rnd, mp_bitsused(&key->n), RSA_MAX_SIZE);
DECL_MP_INT_SIZE_DYN(rndi, mp_bitsused(&key->n), RSA_MAX_SIZE);
#endif /* WC_RSA_BLINDING && !WC_NO_RNG */
Expand Down Expand Up @@ -2627,9 +2628,31 @@ static int RsaFunctionPrivate(mp_int* tmp, RsaKey* key, WC_RNG* rng)
#endif /* RSA_LOW_MEM */

#if defined(WC_RSA_BLINDING) && !defined(WC_NO_RNG)
/* unblind */
if (ret == 0 && mp_mulmod(tmp, rndi, &key->n, tmp) != MP_OKAY)
/* Multiply result (tmp) by bliding invertor (rndi).
* Use Montogemery form to make operation more constant time.
*/
if ((ret == 0) && (mp_montgomery_setup(&key->n, &mp) != MP_OKAY)) {
ret = MP_MULMOD_E;
}
if ((ret == 0) && (mp_montgomery_calc_normalization(rnd, &key->n) !=
MP_OKAY)) {
ret = MP_MULMOD_E;
}
/* Convert blinding invert to Montogmery form. */
if ((ret == 0) && (mp_mul(rndi, rnd, rndi) != MP_OKAY)) {
ret = MP_MULMOD_E;
}
if ((ret == 0) && (mp_mod(rndi, &key->n, rndi) != MP_OKAY)) {
ret = MP_MULMOD_E;
}
/* Multiply result by blinding invert. */
if ((ret == 0) && (mp_mul(tmp, rndi, tmp) != MP_OKAY)) {
ret = MP_MULMOD_E;
}
/* Reduce result. */
if ((ret == 0) && (mp_montgomery_reduce_ct(tmp, &key->n, mp) != MP_OKAY)) {
ret = MP_MULMOD_E;
}

mp_forcezero(rndi);
mp_forcezero(rnd);
Expand Down Expand Up @@ -3520,8 +3543,9 @@ static int RsaPrivateDecryptEx(const byte* in, word32 inLen, byte* out,
mgf, label, labelSz, saltLen,
mp_count_bits(&key->n), key->heap);
#endif
if (rsa_type == RSA_PUBLIC_DECRYPT && ret > (int)outLen)
if (rsa_type == RSA_PUBLIC_DECRYPT && ret > (int)outLen) {
ret = RSA_BUFFER_E;
}
else if (ret >= 0 && pad != NULL) {
/* only copy output if not inline */
if (outPtr == NULL) {
Expand All @@ -3547,8 +3571,9 @@ static int RsaPrivateDecryptEx(const byte* in, word32 inLen, byte* out,
XMEMCPY(out, pad, (size_t)ret);
}
}
else
else {
*outPtr = pad;
}

#if !defined(WOLFSSL_RSA_VERIFY_ONLY)
ret = ctMaskSelInt(ctMaskLTE(ret, (int)outLen), ret, RSA_BUFFER_E);
Expand Down
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