The huge amount of traffic transportable by the next generation optical network is vulnerable to attacks, as is discerned from an alarmingly increase of incidents. The types of attack are expected to range from the typical eavesdropping and service denial to more sophisticated source mimicking. As a consequence, modem encrypted methods refuge to highly sophisticated methods that emanate from quantum mechanics, known as quantum cryptography. However, the sophistication and elegance of quantum-cryptography makes the assumption that the transmission medium and the components involved on the link are perfect and that the properties of photons and the signal intensity do not change during propagation over many kilometers. Therefore, a practical implementation of Q-C may exhibit its own vulnerabilities due to non-linear interactions between photons and medium. Therefore, in addition to the sophistication of QKD and encryption algorithms, an additional function is needed that detects malicious intervention on the transmission link as well as a countermeasure strategy that outsmarts the attacker. In this paper, we consider a practical optical signal that consists of multiple photons, we consider a pragmatic medium with non-linearities, scattering and absorption centers. We describe a case of service denial with Q-C, a method by which an attack is detected, and we develop a countermeasure strategy outsmarting the attacker. Our method assumes that the data channel is encrypted using sophisticated algorithms.
