Security enhancement for OFDM-UWOC system using three-layer chaotic encryption and chaotic DFT precoding

Security is one of the key issues in communications, but it has not attracted much attention in the field of underwater wireless optical communication (UWOC). This Letter proposes a UWOC encryption scheme with orthogonal frequency division multiplexing (OFDM) modulation, based on the three-layer chaotic encryption and chaotic discrete Fourier transform (DFT) precoding. The three-layer chaotic encryption processes are bit stream diffusion, in-phase/quadrature encryption, and time-frequency scrambling. With multi-fold data encryption, the scheme can create a keyspace of 9.7 x 10(179), effectively resisting brute force attacks and chosen-plaintext attacks. A 3 Gbit/s encrypted OFDM signal is successfully transmitted over a 7 m water channel.