A system-oriented analysis of the encryption efficiency of chaos communication systems consisting of lasers subject to all-optical feedback is presented in this paper. Two codification methods are considered, namely external baseband and subcarrier modulation. The robustness of each codification method to two attack scenarios, which are the filtering of the directly detected signal and the usage of an arbitrary receiver to synchronize and extract the message, is numerically evaluated through error counting. The results show that subcarrier modulation offers a much higher discrimination in bit error rate performance between the authorized receiver and the eavesdropper.
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