An experimental digital communication scheme based on chaotic time-delay system

We develop an experimental system for secure communication with nonlinear mixing of information signal and chaotic signal of a time-delay system. The proposed scheme is based on programmable microcontrollers with digital transmission line. The scheme allows one to transmit and receive speech and musical signals in real time without noticeable distortion. A high quality of extraction of hidden information signal is achieved due to the use of digital elements in the scheme, which ensures identity of the parameters and high stability to noise. We study a possibility of hidden message extraction from a chaotic carrier by a third party in the case of mismatch of the receiver and transmitter parameters.     

An efficient chaotic image encryption based on alternate circular S-boxes

A novel and efficient image encryption algorithm based on chaos and multiple S-boxes is proposed in this paper, in which a set of S-boxes is initially constructed using a chaotic system, and each of the S-boxes is considered as a circular sequence with a head pointer. For each image pixel, an S-box is chosen from the set of S-boxes and used to substitute for the plain pixel to get a cipher pixel, and then the chosen S-box is updated by moving its head pointer forward according to the cipher pixel and a random number. In order to increase the plaintext sensitivity of encryption, the substitution processes are performed in forward direction and backward direction, respectively. This scheme not only offers the high security by employing two directional substitutions and using the different S-boxes for each pixel but also achieves high encryption speed by constructing only a few S-boxes and updating the S-box dynamically and easily. The performance of the proposed algorithm is evaluated using a variety of analysis. Experimental results show that the proposed image encryption algorithm is secure and efficient.     

A novel technique for the construction of strong S-boxes based on chaotic Lorenz systems

In cryptographic systems, the encryption process relies on the nonlinear mapping of original data or plaintext to the secure data. The mapping of data is facilitated by the application of the substitution process embedded in the cipher. It is desirable to have resistance against differential cryptanalysis, which assists in providing clues about the composition of keys, and linear secret system, where a simple approximation is created to emulate the original cipher characteristics. In this work, we propose the use of nonlinear functional chaos-based substitution process which employs a continuous time Lorenz system. The proposed substitution system eliminates the need of independent round keys in a substitution-permutation network. The performance of the new substitution box is evaluated by nonlinearity analysis, strict avalanche criterion, bit independence criterion, linear approximation probability, and differential approximation probability.     

An adaptive observer synchronization using chaotic time-delay system for secure communication

Nonlinear Dynamics - Recently, the time delay has considerable attention in the existence of chaos in the nonlinear dynamical systems. In this paper, we therefore develop a new cascade-coupled...     

Image encryption algorithm based on PGL(2,GF(28)) S-boxes and TD-ERCS chaotic sequence

In this article, we propose a novel image encryption algorithm by using the linear fractional transformation (LFT) substitution boxes and tangent-delay for elliptic reflecting cavity (TD-ERCS) chaotic sequence. In addition, we apply the proposed approach to an image and come to know that the correlation analysis, UACI analysis, and NPCR analysis of proposed algorithm are much improved than many existing techniques and very easy to put into practice.     

A new spatiotemporal chaotic system based on two-dimensional discrete system

Nonlinear Dynamics - Chaos maps are widely used in information security due to some attractive properties, but many low-dimensional chaotic maps have several disadvantages such as small parameter...     

An image encryption scheme based on time-delay and hyperchaotic system

In this paper, a novel image encryption scheme based on time-delay and hyperchaotic system is suggested. The time-delay phenomenon is commonly observed in daily life and is incorporated in the generation of pseudo-random chaotic sequences. To further increase the degree of randomness, the output of the hyperchaotic system is processed before appending to the generated sequence. A novel permutation function for shuffling the position index, together with the double diffusion operations in both forward and reverse directions, is employed to enhance the encryption performance. Experimental results and security analyses show that the proposed scheme has a large key space and can resist known-plaintext and chosen-plaintext attacks. Moreover, the encryption scheme can be easily modified to adopt other hyperchaotic systems under the same structure.     

An efficient approach for the construction of LFT S-boxes using chaotic logistic map

In this paper, we synthesize substitution boxes by the use of chaotic logistic maps in linear fractional transformation. In order to introduce randomness in the construction of S-boxes, the data from the chaotic system is used in linear fractional transformation to add additional unpredictable behavior. The proposed S-box is tested for its strength in encryption applications. The nonlinearity characteristic of the proposed S-box is studied, and the strength of the cipher is quantized in terms of this property. In addition, the behavior of bit changes at the output of the cipher in comparison with the input is also studied. Similarly, the input/output differential is also evaluated for different bit patterns. The results of statistical analyses show superior performance of the proposed S-boxes.     

Implementation of chaotic circuits with a digital time-delay block

In this paper, the implementation of time-delay chaotic circuits is investigated. To implement the time-delay block, a solution based on a digital circuitry has been adopted. This solution leads to a programmable hardware which can be realized by using available field programmable gate arrays. In this paper, issues raised from this implementation such as the behavior of the system with respect to the precision and the sampling rate of the conversion process have been investigated. The synchronization error is proposed as an indicator of the accuracy of the whole implementation.     

Linear feedback controller design method for time-delay chaotic systems

Based on the stability theory of time-delay systems, this paper discusses chaos control and synchronization problem of time-delay chaotic systems. Through the combining of a new theorem and the characters of the chaotic system, we have designed a linear controller to realize chaos control and synchronization for Lorenz system with time-varying lags. Finally, numerical simulations are provided to verify the effectiveness and feasibility of the developed method.     

Designing a multi-scroll chaotic system by operating Logistic map with fractal process

Recently, chaotic systems have been widely investigated in several engineering applications. This paper presents a new chaotic system based on Julia’s fractal process, chaotic attractors and Logistic map in a complex set. Complex dynamic characteristics were analyzed, such as equilibrium points, bifurcation, Lyapunov exponents and chaotic behavior of the proposed chaotic system. As we know, one positive Lyapunov exponent proved the chaotic state. Numerical simulation shows a plethora of complex dynamic behaviors, which coexist with an antagonist form mixed of bifurcation and attractor. Then, we introduce an algorithm for image encryption based on chaotic system. The algorithm consists of two main stages: confusion and diffusion. Experimental results have proved that the proposed maps used are more complicated and they have a key space sufficiently large. The proposed image encryption algorithm is compared to other recent image encryption schemes by using different security analysis factors including differential attacks analysis, statistical tests, key space analysis, information entropy test and running time. The results demonstrated that the proposed image encryption scheme has better results in the level of security and speed.     

Lag synchronization for fuzzy chaotic system based on fuzzy observer

A new fuzzy observer for lag synchronization is given in this paper. By investi- gating synchronization of chaotic systems, the structure of drive-response lag synchronization for fuzzy chaos system based on fuzzy observer is proposed. A new lag synchronization criterion is derived using the Lyapunov stability theorem, in which control gains are obtained under the LMI condition. The proposed approach is applied to the well-known Chen＇s systems. A simulation example is presented to illustrate its effectiveness.     

Parameter estimation for time-delay chaotic systems by hybrid biogeography-based optimization

It is an important issue to estimate parameters of chaotic systems in nonlinear science. In this paper, delay time as well as parameters of time-delay chaotic system is considered by treating delay time as an additional parameter. The parameter estimation problem is formulated as a multidimensional optimization problem, and an effective hybrid biogeography-based optimization is developed to solve this problem. Numerical simulations are conducted on two typical time-delay chaotic systems to show the effectiveness of the proposed scheme.     

Synchronization between integer-order chaotic systems and a class of fractional-order chaotic system based on fuzzy sliding mode control

In this paper, we focus on the synchronization between integer-order chaotic systems and a class of fractional-order chaotic system using the stability theory of fractional-order systems. A new fuzzy sliding mode method is proposed to accomplish this end for different initial conditions and number of dimensions. Furthermore, three examples are presented to illustrate the effectiveness of the proposed scheme, which are the synchronization between a fractional-order Lü chaotic system and an integer-order Liu chaotic system, the synchronization between a fractional-order hyperchaotic system based on Chen??s system and an integer-order hyperchaotic system based upon the Lorenz system, and the synchronization between a fractional-order hyperchaotic system based on Chen??s system, and an integer-order Liu chaotic system. Finally, numerical results are presented and are in agreement with theoretical analysis.