Physical layer encryption based on digital chaos in THz wireless communication

Abstract

In this paper, we propose and implement a digital chaos-based encryption scheme that enhances the security of free space communication in a photonics-assisted terahertz wave (THz-wave) wireless data transmission system operating at 340 GHz. We experimentally demonstrate that the delivery of traditional and encrypted 16 Gbaud 16QAM-OFDM and PS-64QAM-OFDM (5.5 bit/symbol) signals over 20 km of standard single mode fiber (SSMF) and a wireless distance 25/54 m. The bit-error ratio (BER) performance of each signal meets the soft-decision forward-error-correction (SD-FEC) threshold of 4.2 × 10⁻². The experimental results show that the encryption scheme does not degrade the performance of the OFDM signals. Furthermore, we analyze the encryption algorithm’s security based on Kerckhoff’s principle, which states that a tiny deviation from the correct keys would make the eavesdropper unable to obtain useful information, and the BER would remain around 0.5. The proposed encryption scheme based on a digital three-dimensional multi-scroll chaotic system, has a huge key space of size 2¹⁴⁵ bits, which can effectively prevent exhaustive key-search attacks.