Shihan Sajeed

Imperfections in the receiver setup of quantum cryptography systems may allow an eavesdropper to use it as a control parameter to attack the system. Mismatch of sensitivity in the receiver's photodetectors is one of the imperfections that can potentially be exploited by an eavesdropper. Published researches have shown that scrambling the role of the photodetectors in the receiver can be one of the countermeasure strategies to protect the system. In this work, we show that the proposed countermeasure can be bypassed if the attack is generalized by including more attack variables. Using experimental results from existing publications, we show that detector randomization effectively prevents the initial attack but fails to do so when Eve generalizes her attack strategy. Thus, unless new techniques are proposed to strengthen the existing detector-scrambling countermeasure strategies, it cannot guarantee security against detector efficiency mismatch based attacks. Our result and methodology could be used to security-certify a free-space quantum communication receiver against all types of detector-efficiency-mismatch type attacks.