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Reject zero modulus in mulmod/sqrmod #11065

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8 changes: 8 additions & 0 deletions wolfcrypt/src/port/maxim/max3266x.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2495,6 +2495,10 @@ int hw_mulmod(mp_int* multiplier, mp_int* multiplicand, mp_int* mod,
return MP_VAL;
}
if ((multiplier->used == 0) || (multiplicand->used == 0)) {
/* A zero modulus is invalid whatever the operands are. */
if (mod->used == 0) {
return MP_VAL;
}
mp_zero(result);
return 0;
}
Expand Down Expand Up @@ -2591,6 +2595,10 @@ int hw_sqrmod(mp_int* base, mp_int* mod, mp_int* result)
return MP_VAL;
}
if (base->used == 0) {
/* A zero modulus is invalid whatever the base is. */
if (mod->used == 0) {
return MP_VAL;
}
mp_zero(result);
return 0;
}
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23 changes: 21 additions & 2 deletions wolfcrypt/src/sp_int.c
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Original file line number Diff line number Diff line change
Expand Up @@ -12292,6 +12292,7 @@ int sp_mul(const sp_int* a, const sp_int* b, sp_int* r)
* @param [out] r SP integer result.
*
* @return MP_OKAY on success.
* @return MP_VAL when m is 0.
* @return MP_MEM when dynamic memory allocation fails.
*/
static int _sp_mulmod_tmp(const sp_int* a, const sp_int* b, const sp_int* m,
Expand All @@ -12300,7 +12301,15 @@ static int _sp_mulmod_tmp(const sp_int* a, const sp_int* b, const sp_int* m,
int err = MP_OKAY;

if (sp_iszero(a) || sp_iszero(b)) {
_sp_zero(r);
/* Only reached from sp_mulmod() when the result aliases the modulus.
* The zero-operand short-circuit would otherwise bypass the sp_mod()
* validation that the non-zero operand path relies on. */
if (sp_iszero(m)) {
err = MP_VAL;
}
else {
_sp_zero(r);
}
}
else {
/* Create temporary for multiplication result. */
Expand Down Expand Up @@ -12334,6 +12343,7 @@ static int _sp_mulmod_tmp(const sp_int* a, const sp_int* b, const sp_int* m,
* @param [out] r SP integer result.
*
* @return MP_OKAY on success.
* @return MP_VAL when m is 0.
* @return MP_MEM when dynamic memory allocation fails.
*/
static int _sp_mulmod(const sp_int* a, const sp_int* b, const sp_int* m,
Expand Down Expand Up @@ -17501,14 +17511,23 @@ int sp_sqr(const sp_int* a, sp_int* r)
* @param [out] r SP integer result.
*
* @return MP_OKAY on success.
* @return MP_VAL when m is 0.
* @return MP_MEM when dynamic memory allocation fails.
*/
static int _sp_sqrmod(const sp_int* a, const sp_int* m, sp_int* r)
{
int err = MP_OKAY;

if (sp_iszero(a)) {
_sp_zero(r);
/* Only reached from sp_sqrmod() when the result aliases the modulus.
* The zero-operand short-circuit would otherwise bypass the sp_mod()
* validation that the non-zero operand path relies on. */
if (sp_iszero(m)) {
err = MP_VAL;
}
else {
_sp_zero(r);
}
}
else {
/* Create temporary for multiplication result. */
Expand Down
33 changes: 33 additions & 0 deletions wolfcrypt/test/test.c
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Original file line number Diff line number Diff line change
Expand Up @@ -75903,6 +75903,39 @@ static wc_test_ret_t mp_test_mulmod_sqrmod(mp_int* a, mp_int* b, mp_int* m,
if (!mp_iszero(m))
return WC_TEST_RET_ENC_NC;

/* A zero modulus is invalid whether or not the result aliases it. The
* zero-operand short-circuits must not hide it. */
ret = mp_set(a, 0);
if (ret == MP_OKAY)
ret = mp_set(b, 0x5);
if (ret == MP_OKAY)
ret = mp_set(m, 0);
if (ret != MP_OKAY)
return WC_TEST_RET_ENC_EC(ret);
if (mp_sqrmod(a, m, r) != WC_NO_ERR_TRACE(MP_VAL))
return WC_TEST_RET_ENC_NC;
if (mp_sqrmod(a, m, m) != WC_NO_ERR_TRACE(MP_VAL))
return WC_TEST_RET_ENC_NC;
ret = mp_set(m, 0);
if (ret != MP_OKAY)
return WC_TEST_RET_ENC_EC(ret);
if (mp_mulmod(a, b, m, r) != WC_NO_ERR_TRACE(MP_VAL))
return WC_TEST_RET_ENC_NC;
if (mp_mulmod(a, b, m, m) != WC_NO_ERR_TRACE(MP_VAL))
return WC_TEST_RET_ENC_NC;
/* Cover the other half of the zero-operand test in _sp_mulmod_tmp. */
ret = mp_set(a, 0x5);
if (ret == MP_OKAY)
ret = mp_set(b, 0);
if (ret == MP_OKAY)
ret = mp_set(m, 0);
if (ret != MP_OKAY)
return WC_TEST_RET_ENC_EC(ret);
if (mp_mulmod(a, b, m, r) != WC_NO_ERR_TRACE(MP_VAL))
return WC_TEST_RET_ENC_NC;
if (mp_mulmod(a, b, m, m) != WC_NO_ERR_TRACE(MP_VAL))
return WC_TEST_RET_ENC_NC;

return 0;
}

Expand Down
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