A 7-D Hyperchaotic System-Based Encryption Scheme for Secure Fast-OFDM-PON

In this paper, we propose and experimentally demonstrate a novel two-step I/Q-encryption scheme for improving physical layer security in fast orthogonal frequency division multiplexing passive optical network (fast-OFDM-PON). To meet the requirement of this encryption scheme and further enhance the security, a seven-dimensional hyperchaotic system with five positive Lyapunov exponents is designed. In this system, Walsh-Hadamard transform and discrete cosine transform are chosen to reduce the computation complexity and increase the key space simultaneously. An optional discrete Fourier transform spread is required to achieve the maximum scrambling degree. Encryption of 9.4-Gb/s 16-quadrature amplitude modulation fast-OFDM signals with a total key space of ~10 788 against the exhaustive trial has been successfully implemented over 50-km standard single mode fiber in a fast-OFDM-PON, which shows good resistance against illegal access to optical network units. All the results indicate that this proposed encryption scheme has improved security performance with relatively low computation complexity.