int mp_invmod_mont_ct (mp_int * a, mp_int * b, mp_int * c, mp_digit mp)
{
  return fp_invmod_mont_ct(a, b, c, mp);
}
The product behaves differently or sends different responses under different circumstances in a way that is observable to an unauthorized actor, which exposes security-relevant information about the state of the product, such as whether a particular operation was successful or not.