We propose an optical encryption technique where the data is encrypted with wideband analog noise. Matching both the phase and amplitude of the noise is required, providing a large key space for the encryption process.
The growing awareness of the vulnerability of information transmitted on communication systems within the government, military and commercial sectors, has stimulated a number of areas of research within the optical community to design optical hardware encryption systems providing inherent immunity to espionage techniques. This paper describes a hardware optical encryption technique that utilises off the shelf telecommunication equipment and negates the necessity for an independent key distribution system with respect to the data transmission system, as is common with alternative encryption system implementations. This method also lends itself easily to fiber optic or free space communication and is applicable within any optical waveband. The encryption-decryption of the optical signal is achieved through low coherence optical interferometry. This requires the instantaneous processing and analysis of the signal, optically, to retrieve the relevant optical phase information hidden in the transmitted optical noise. This technology allows an authorised user to transmit encrypted information at a high data rate securely, while maintaining opaqueness to an unauthorised observer that data transmission is occurring. As the instantaneous optical field properties of the signals present in the system are essential to the optical encryption - decryption process, the system is inherently protected against electronic recording and advances in computational decryption algorithms. For organisations wishing to protect sensitive data and levels of communication activity these are highly desirable features.
We propose and demonstrate an advanced optical modulation format that makes use of both spectral and temporal phase encodings (2-D) for applications requiring exceptional security. The method combines modulation techniques used in direct-sequence spread-spectrum coding, spectral-phase encoding, and M-ary phase-shift keying with codes generated using cryptographically secure pseudorandom number generators. The wideband transmission signal is very difficult for an eavesdropper to record or analyze. Signal-to-noise ratio limitations imposed by quantum effects enhance the security further. The properties of the transmitted signal make it especially useful for physics-based key expansion systems. We have successfully used this setup to transmit encrypted 155 Mb/s data over 70 km of fiber with a BER value of 4E-5.
Security enhancement is a major challenge in future 6G wireless networks. In this study, we have introduced a symmetric-key encryption system, which utilizes multilevel signaling, for the security of microwave signals against wireless interception. The system achieves quantum-noise signal masking at microwave frequencies via optical-tomicrowave frequency conversion based on the homodyne process, thus providing high signal security. We show experimental demonstrations of quantum-noise randomized phase-shift keying modulation/quadrature amplitude modulation cipher generation at a frequency of ~GHz via the intensity modulation/direct detection analog intermediate frequency over fiber transmission. The proposed system simultaneously achieves microwave signal delivery over a fiber link and signal encryption based on sufficient quantum-noise signal masking for wireless communication systems.