A Physical Layer Chaotic Encryption Method for a Wireless OFDM system

Upper-Ilayer cryptographic techniques are commonly used to ensure secure data transmission over wireless networks by encrypting information at the software level. However, wireless transmissions remain vulnerable to passive and active attacks. To address this issue, research has been conducted on physical layer encryption (PLE). Unlike traditional upper-layer encryption, which operates at the bit level, PLE obscures the transmitted signal, making it more challenging for eavesdroppers to decipher. This paper proposes a novel physical layer chaotic encryption method designed to obfuscate the modulation scheme used in orthogonal frequency division multiplexing (OFDM) systems. The proposed scheme leverages a chaotic system, the three-dimensional logistic-sine cascading map (3D-LSCM), to scramble constellation points. The method improves upon previous work by incorporating histogram equalisation to evenly distribute the output of the chaotic system, thereby better obfuscating the modulation scheme. Experimental results obtained using the ADALM-PLUTO with an OFDM signal demonstrate the effectiveness of the encryption scheme in concealing modulation types, such as Quadrature Amplitude Modulation (QAM), from potential eavesdroppers. The encryption demonstrates high key sensitivity, statistical independence, and large key space, highlighting its robustness against brute-force attacks.