We consider a scenario of spontaneous parametric down-conversion to generate entangled states that are used for quantum communications. Such a mechanism is vulnerable to attacks caused by an adversary that may inject power to the nonlinear crystal to drive the operating point away from maximum fidelity. We devise a low-cost strategic mechanism to counteract this attack, which corresponds to lowering the injected power anticipating the attack. If the attacker is also rational, this leads to a strategic interaction that can be studied with game theory. We show how the strategic response of the transmitter can mitigate the extent of the attack when it is not too strong.