Encrypted Signal Research Articles

Analog–Digital Combined High-Secure Optical Communication System Based on Chaotic Circuit Driving

We propose and demonstrate a new analog–digital combined high-secure optical communication system based on chaotic circuit driving, which achieves encryption in the analog and digital domains. A 3D chaotic system is used for analog domain phase encryption (ADPE) and digital domain time–frequency encryption (DDTFE) simultaneously. The ADPE is carried out by the privately chaotic signal driving the phase modulator (PM), which realizes chaotic phase encryption. The chaotic circuit comprehends highly complex nonlinear dynamics. Its size is 10 cm × 5 cm, which has the characteristics of small size and low cost. The DDTFE is performed by the frequency–time encryption of signals in the digital domain. The experimental results show that the optical physical layer encryption scheme based on analog and digital combination can successfully mask the original data. The driving signal of PM is that generated by the chaotic circuit and needs to be privately synchronized, so that the legal receiver may accurately decrypt the encrypted data and the eavesdropper is unable to intercept a valuable message. If the chaotic driving circuit produces a delay of 3 s, the bit error rate (BER) reaches more than 0.3 at the receiver. The results of experiment verify that the scheme can transmit 13.3 Gb/s 16 quadrature amplitude modulation orthogonal frequency division multiplexing (16QAM-OFDM) signal over 25 km standard single mode fiber (SSMF). This scheme achieves low-cost, high-security communication, making it a suitable foundation for high-speed, secure optical communication at the physical layer.

Optical non-orthogonal multiple access based on amino acids and extended zigzag.

We propose a novel security-enhanced power division multiplexing (SPDM) optical non-orthogonal multiple access scheme in conjunction with seven-core optical fiber in this paper. This scheme could improve the security of data transmission at the physical layer and the split ratio of the access network, ensuring more users can be served at the same time. Additionally, multiple signals can be superimposed in the digital domain, leading to a significant improvement in spectral efficiency. We have further experimentally demonstrated the transmission of 47.25 Gb/s SPDM orthogonal frequency division multiplexing (OFDM) signals in a 2 km seven-core fiber system. The experimental results confirm that our scheme can increase the number of access users by 14 times without influencing the privacy of different users. It is worth mentioning the signal encryption method based on amino acids combine with extended zigzag is proposed for the first time as we know. Meanwhile, the key space reaches 10182, indicating that the data transmission process can be effectively protected from the attack of stealers. The proposed security-enhanced power division multiplexing space division multiplexing passive optical network (SPDM-SDM-PON) support multi-threading and multi-functions, showing a great potential to be applied in the future telecommunication systems.

Autonomous jerk oscillator with sine nonlinearity and logistic map for sEMG encryption

This research discusses the dynamical behaviors of the autonomous jerk oscillator with sine nonlinearity (AJOSN) and its application to secure s-EMG (Surface ElectroMyoGraphic) data. The AJOSN has two or no-equilibrium points, and the stability of the two equilibrium points indicates that one is stable and the other is unstable. The AJOSN reveals fast-spiking and periodic bursting, relaxing and periodic oscillations, hidden chaotic attractors and coexisting attractors. The numerical analysis results are validated by the Field Programmable Gate Array (FPGA) implementation. Finally, the AJOSN’s chaotic behavior coupled with the logistic map is exploited to encrypt the s-EMG signals. The proposed encryption and decryption method consists of simultaneously encrypting the sEMG signal. The sEMG signal, once transformed into 2D as a grayscale image, undergoes first encryption based on the chaotic signal generated by the AJOSN (Autonomous jerk oscillator with sine nonlinearity) model. The encrypted signal obtained from this first part is called ‘Jerk encrypted signal.’ The second part is to encrypt the ‘Jerk Encrypted Signal’ by the chaotic logistics map. The encryption and decryption results obtained are quite encouraging and offer a great prospect.

Secondary-encryption optical chaotic communication system based on one driving laser and two responding lasers

This paper theoretically investigates a secondary-encryption optical chaotic communication system scheme based on an optical injection structure with single optical feedback and dual-dispersion optical feedback lasers. In the scheme, a fiber reflector (FR) and Fabry–Perot interferometer (FPI) are selected as the laser feedback cavity and effectively conceals time delay signatures (TDSs) of the generated chaotic signals. By switching the responding laser connected to the driving laser with the message feeding method, messages directly participating in the process of encryption signal generation are avoided to generate the first encrypted chaotic sequence that can characterize a message. Subsequently, chaotic phase disturbance technology is used to complete the secondary encryption. By virtue of the spectral broadening effect of chaotic phase disturbance, the message rate and the randomness of the encrypted signal can be effectively enhanced. We use the synchronous power error to decrypt the message at the receiver, which simplifies the system structure and realizes the scheme with low hardware costs. The proposed scheme overcomes the shortcomings of existed schemes, which generate chaotic signal sensitive to channel noise and have complex system structures. In addition, the proposed scheme shows good robustness in terms of handling noise for transmitting digital signals, a bit error rate (BER) of 6.7 × 10−4 at a simulation signal-to-noise ratio of 10 dB, and good application prospects in harsh transmission environments, such as submarine optical fiber transmission.

Nonlinear Control and Circuit Implementation in Coupled Nonidentical Fractional-Order Chaotic Systems

In this paper, circuit implementation and anti-synchronization are studied in coupled nonidentical fractional-order chaotic systems where a fractance module is introduced to approximate the fractional derivative. Based on the open-plus-closed-loop control, a nonlinear coupling strategy is designed to realize the anti-synchronization in the fractional-order Rucklidge chaotic systems and proved by the stability theory of fractional-order differential equations. In addition, using the frequency-domain approximation and circuit theory in the Laplace domain, the corresponding electronic circuit experiments are performed for both uncoupled and coupled fractional-order Rucklidge systems. Finally, our circuit implementation including the fractance module may provide an effective method for generating chaotic encrypted signals, which could be applied to secure communication and data encryption.

Demonstration of the high-security 3D-CAP scheme in multi-core fiber transmission

In this paper, the high-security three-dimensional (3D) carrier-less amplitude-phase (CAP) modulation based on 3D space constellation masking in multi-core fiber (MCF) transmission is proposed. Logistic Map model and Four-wing hyper-chaotic systems are employed to implement bit-level encryption, displacement masking, and space masking. This way, we achieved a key space of 1 × 1083 size, which resists violent attacks, and improves the physical layer security of the system. The superposition combined two chaotic models reduces the difficulty of implementation and enables more security for constellation encryption. A 280 Gb/s encrypted 3D-CAP32 signal transmission over 2.5 km MCF is experimentally demonstrated. The experimental results show that the proposed scheme can effectively resist illegal attack from an un-authorized optical network unit (ONU), and compared with an unencrypted 3D-CAP32 signal, the encrypted 3D-CAP32 signal has a receiver sensitivity penalty of 0.38 dB in a back-to-back configuration at a BER of 1 × 10−3. It is a strong candidate for the future highly-secured optical access network.

Secure OFDM-PON using three-dimensional selective probabilistic shaping and chaos.

In this paper, a novel three-dimensional selective probabilistic shaping (3D-SPS) and chaos-based multi-stage encryption scheme is proposed for physical layer security enhancement and transmission performance improvement in orthogonal frequency division multiplexing-based passive optical network (OFDM-PON). On the basis of inherent randomness of symbol sub-sequences with low granularity, the SPS algorithm is performed on the employed cubic constellation within each sub-sequence. Consequently, the probability distribution of inner points significantly increases after the constellation region exchange according to various rules. The generated compressed shaping information (CSI) is encrypted and used as the synchronization head for transmission. Furthermore, 3D scrambling is performed while maintaining the shaping effect. The encrypted signals of 35.3 Gb/s are successfully transmitted over a 25-km standard single-mode fiber (SSMF) and a back-to-back (BTB) system. The results show that by selecting the appropriate system parameter, the proposed scheme can provide about 2.4 dB modulation gain on the received optical power at a bit error rate (BER) of 10‒3 compared with a conventional quadrature amplitude modulation (QAM) signal under the same bit rate, and 0.9 dB shaping gain is brought due to the SPS. The encryption method possesses a relatively low computational complexity and sufficient key space of 10120 is introduced to resist exhaustive attack.

Experimental Analysis of GPS L2C Signal Quality under Various Observational Conditions

To appropriately handle the GPS L2C signal for the future development of positioning algorithms, this contribution has endeavoured to figure out its features by computing some quality measures of all the modernised satellites (i.e., twenty-three as of January 2022) and comparing them with those of the C/A and P2(Y) code. A series of quality analyses have been carried out to GPS measurements at twenty-four continuously operating reference stations (CORS) equipped with eight receiver models. In addition, experimental data acquired by a combination of high-end and cost-effective receivers have been intensively assessed to characterise the relative signal quality of the L2C to the legacy codes. The observational conditions considered in this study include different multipath environments and receiver dynamics. The results of the analyses, in general, indicate that the quality of the L2C-derived measurements is equivalent to the legacy civilian code (i.e., C/A) but superior to the encrypted military signal (P2(Y)). Hence, it is expected that the new civilian GPS signal enhances the positioning performance of dual-frequency measurements with both high-end and cost-effective receivers.

Block compressive sensing chaotic embedded encryption for MCF-OFDM transmission system.

In this paper, we propose a block compressive sensing (BCS) based chaotic embedded encryption scheme for multi-core fiber orthogonal frequency division multiplexing (MCF-OFDM) system. BCS technology is used to recover the entire desired information from the small amounts of data. Meanwhile, a four-dimensional discrete chaotic encryption model generates four masking factors, which are respectively used for coefficient random permutation (CRP), measurement matrix, diffusion and singular value decomposition (SVD) embedding to achieve ultra-high security encryption of four different dimensions. In terms of compressive sensing, CRP can make the discrete cosine transform (DCT) coefficient distribute randomly to improve the sampling efficiency of BCS. Compared with the data without compressive sensing, the data volume is reduced by 75%. In chaotic encryption, SVD technology embeds secret images of noise-like after initial encryption into carrier images to generate encrypted images with visual security. The key space reaches 10120 and it realizes the dual protection of source image data and external representation. The proposed scheme using a 2km 7-core optical fiber achieves a 78.75 Gb/s transmission of encrypted OFDM signals. The received optical power is greater than -14 dBm, and the bit error rate (BER) of core1-core7 is lower than 10-3. When the compression ratio sets to 0.25 and the attack range of encrypted data is up to 30%, the image can still recover the outline and general information. The experimental results show that this scheme can improve the security performance and reduce the complexity of information transmission system. Furthermore, the scheme combines The BCS chaotic embedded encryption technology with MCF-OFDM system, which has a good application prospect in the future optical networks.

Secure OFDM transmission scheme based on chaotic encryption and noise-masking key distribution.

In this Letter, we propose a secure orthogonal frequency division multiplexing (OFDM) transmission scheme based on chaotic encryption and noise-masking key distribution. With the implementation of a three-dimensional digital chaotic system, the security performance is effectively enhanced by scrambling the phase, symbol, and subcarrier frequency of the OFDM signal. The proposed noise-masking key distribution can mask the key information of the chaotic system into noise and transmit it with the chaotic encrypted signal simultaneously. By this mechanism, the legal receiver can realize uninterrupted authentication and decryption even if the key is constantly updated. Transmission of a 62.2-Gb/s quadrature phase shift keying (QPSK) and 124.4-Gb/s 16 quadrature amplitude modulation (16QAM) OFDM signal over a 2-km 7-core fiber using the proposed scheme is experimentally demonstrated. The results show that the proposed scheme can realize security enhancement and cost-effective key distribution without significant bit error ratio (BER) performance degradation.

Image Encryption and Decryption Using Chua’s Circuits

In recent years, chaos studies have been developing tremendously. The importance of using chaos is its deterministic nature. Though the chaos is interpreted as random in nature but it is deterministic. This is a very useful aspect that can be used in encryption of signals. In this paper, the very well-known Chua’s circuit is used to generate random sequences based on initial conditions. These sequences are going to be used for encrypting and decrypting an image. The key is going to be encrypted using a function with a modulus operation then used as an initiation for Chua circuit. The output of Chua circuit is three arrays X, Y, and Z. The process can be divided into two steps. First, one of these sequences is going to be used to form 2D array and the other two sequences also form another 2D array where both have the same size. Then, it is going to be XORed with the image and then the rows and the columns are going to be swapped horizontally and vertically. Second, the other matrix coming from X-Y arrays after mod operation is going to be used as an index for the first processed image. Simulation results show that the scheme sensitivity and complexity to such factors. The importance of this method is that it has plenty of factors that can be unique during generating of these chaotic sequences which makes it very difficult to decrypt the message.

Secure audio signal encryption based on triple compound-combination synchronization of fractional-order dynamical systems

Secure audio signal encryption based on triple compound-combination synchronization of fractional-order dynamical systems

Chaotic physical security strategy based on manifold learning-assisted GANs for SDM-OFDM-PONs.

In this paper, we propose a high-security spatial division multiplexing orthogonal frequency division multiplexing passive optical network (SDM-OFDM-PON) encryption scheme based on manifold learning-assisted generative adversarial networks (MFGANs). The chaotic sequences generated by MFGANs are applied to produce the masking vectors to encrypt the constellation and frequency. With the help of manifold learning, the proposed scheme can learn the complex structures from various chaotic models and makes use of more parameters than a single traditional model to achieve the large key space of 1 × 10183. A 70 Gb/s encrypted OFDM signal transmission over 2 km 7-core fiber was experimentally demonstrated. In addition, due to the capacity of parallel computing of graphics processing units (GPUs), the encryption time by the proposed scheme is around 1.38% of the conventional encryption scheme. It is therefore shown that the proposed encryption scheme can ensure both efficiency and security in SDM-OFDM-PON systems.

A deep learning based malicious module identification using stacked sparse autoencoder network for VLSI circuit reliability

The rate of development of technology and its associated security issues are increasing in integrated circuit industry. This provides a space for implanting dormant nature of threats, named Hardware Trojan (HT) in various process of integrated circuits (IC) design. The impact of HT’s emanates the encrypted signals, privacy disruption, performance degradation or denial of service. The threat models are unimaginable and it can be intruded at any stage which complicates the HT detection process. Therefore, a deep learning-based malicious module identification method is proposed in this work by implementing stacked autoencoder and stacked sparse autoencoder model. The simulation results shows that the proposed stacked sparse autoencoder outperforms the best in detecting the malicious modifications with an average accuracy of 97.53%, true positive rate of 93% and moreover the true negative rate achieved is 98.14% which proves the effectiveness of sparsity nature in extracting suitable features in the proposed schemes.

Simultaneous Realization of Dynamic and Hybrid Multiplexed Holography via Light‐Activated Chiral Superstructures

AbstractAs a well‐recognized technology for optical data encoding and extracting, holography has faced an ever‐growing pursuit in the miniaturization, multifunctionality, and tunability for today's abundant information. Despite infusive achievements in metahologram, simultaneous realization of dynamic tunability and high‐dimensional multiplexing is critical yet lagging behind, which becomes one bottleneck for this emerging frontier. Here, an innovative solution is proposed by integrating the limited penetration depth of light in chiral liquid crystals and their intrinsic stimuli‐responsive characteristics. Based on a photoactive chiral dopant and the asymmetric photopatterning boundary confined self‐organization, light‐activated spectrally tunable, polarization‐ and direction‐dependent holograms are created simultaneously. As a promising example for information technology, an encrypted signal light is demonstrated, where the wavelength, propagation direction, helicity of light, and reaction duration serve as customized keys for information decryption. This work extends the construction of soft hierarchical superstructures and offers a satisfactory and open‐ended scheme for the intelligent holography, inspiring advanced display, security, and communication.

IF-Over-Fiber Transmission of OFDM Quantum-Noise Randomized PSK Cipher for Physical Layer Encryption of Wireless Signals

This study proposes an intensity modulation/direct detection intermediate frequency-over-fiber (IFoF) system that generates a microwave orthogonal frequency-division multiplexing (OFDM) quantum-noise randomized phase-shift-keying (PSK) cipher. The system directly prevents wireless interception by an eavesdropper without a private key. We theoretically analyze the system and derive a fundamental tradeoff between the security and signal quality at an intermediate frequency (IF). The system achieves balanced security and signal quality. We experimentally demonstrate 4.09-Gbit/s PSK cipher generation at an IF of 3.6 GHz. The cipher has 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">16</sup> phase levels, and more than 100 adjacent signals are masked by quantum noise. The quantum-noise signal masking imposes irreducible uncertainty on illegitimate reception of the cipher, and a symbol error ratio (SER) that an eavesdropper can reach approaches 1. A lower bound of the SER is promised because truly random signal masking by quantum noise cannot be reduced. The error vector magnitude of the IF signals after decryption is maintained at a low value for wireless transmission. The cipher directly and effectively protects the wireless transmission of personal data from interception.

Josephson Junction Model: FPGA Implementation and Chaos-Based Encryption of sEMG Signal through Image Encryption Technique

The field programmable gate array (FPGA) implementation of the nonlinear resistor-capacitor-inductor shunted Josephson junction (NRCISJJ) model and its application to sEMG (Surface ElectroMyoGraphic) signal encryption through image encrypted technique are reported in this study. Thanks to the numerical simulations and FPGA implementation of the NRCISJJ model, different shapes of chaotic attractors are revealed by varying the parameters. The chaotic behaviour found in the NRCISJJ model is used to encrypt the sEMG signal through image encryption technique. The results obtained are interesting and open up many perspectives.

One-time pad scheme based on polar code and OFDM for MMW-RoF system at W-band.

The physical layer security of millimeter-wave radio-over-fiber (MMW-RoF) system at W-band is a promising topic. This paper experimentally demonstrates a one-time pad scheme based on polar code and orthogonal frequency division multiplexing (OFDM) for MMW-RoF system. In the proposed scheme, the initial key is obtained by looking-up table mapping randomly, and chaotic sequence is generated by using 4-D cellular neural network (CNN). The key for next frame is placed in the partial frozen bits of polar code, which can realize the one-time pad mechanism. The encrypted OFDM signal carried by 100GHz millimeter-wave is successfully transmitted over 50 km standard single-mode fiber (SSMF) and 5 m wireless channel in this experiment. The experimental results show that, compared with the traditional OFDM signal, the proposed scheme in SCL8 decoder can achieve ∼4.1 dB gain at the BER of 10-3, which can effectively use the frozen bits of polar code to transmit more information and improve the security and reliability of the whole system.

A new Secure Speech Communication Scheme Based on Hyperchaotic Masking and Modulation.

This paper presents a new, effective, simple, and more secure speech communication technique based on the combination of hyperchaotic masking and modulation. One hyperchaotic system is used for both masking and modulation operations. Speech communication techniques based on only chaotic masking have weak resistance to several attacks. So, further encryption is applied using chaotic modulation. Second-level encryption has enhanced the security of speech communication, as evidenced by the performance metrics. The encryption correlation coefficient between the original signal and the encrypted signal after chaotic masking is 0.0101. However, the correlation coefficient has become 0.0007 after the second level of encryption. Again, the speech signal segmental spectral signal to noise ratio (SSSNR) is -32.5160 dB after the first level of encryption, but the SSSNR becomes - 47.2612 dB after performing chaotic modulation in the second level of encryption. The decryption process is achieved successfully and the original speech signal is retrieved. The required synchronization is performed using an active controller.

A Secure Communication Scheme of Three-Variable Chaotic Coupling Synchronization Based on DNA Chemical Reaction Networks

Three-variable chaotic synchronization has been implemented based on DNA chemical reaction networks (CRNs) in previous works. However, it is still difficult to realize the encryption and decryption of continuous signals. A scheme of secure communication is proposed based on chaotic coupling synchronization by DNA CRNs in this paper. Firstly, the CRNs of two three-variable chaotic systems are constructed using bimolecular representation. Secondly, according to the design principle of the coupling term and the theory of stability, the CRNs of the coupling term are designed to realize the synchronization of two chaotic systems. Finally, the oblique wave, square wave, and staircase wave signals are added into chaotic systems to realize encryption and decryption. The dynamic behavior of a three-variable chaotic system is verified by Visual DSD and MATLAB software. The synchronization proof and the experimental results of encryption and decryption are given. The results indicate that the proposed secure communication scheme is effective. This paper provides an application method for studying secure communication in the DNA field.