Vinod Patidar

Image encryption using chaotic logistic map

Abstract In recent years, the chaos based cryptographic algorithms have suggested some new and efficient ways to develop secure image encryption techniques. In this communication, we propose a new approach for image encryption based on chaotic logistic maps in order to meet the requirements of the secure image transfer. In the proposed image encryption scheme, an external secret key of 80-bit and two chaotic logistic maps are employed. The initial conditions for the both logistic maps are derived using the external secret key by providing different weightage to all its bits. Further, in the proposed encryption process, eight different types of operations are used to encrypt the pixels of an image and which one of them will be used for a particular pixel is decided by the outcome of the logistic map. To make the cipher more robust against any attack, the secret key is modified after encrypting each block of sixteen pixels of the image. The results of several experimental, statistical analysis and key sensitivity tests show that the proposed image encryption scheme provides an efficient and secure way for real-time image encryption and transmission.

Discrete chaotic cryptography using external key

Abstract In this Letter, we propose a symmetric key block cipher algorithm utilizing the essence of chaos. The proposed cryptosystem does not use explicitly the system parameter or initial condition of the chaotic map as a secret key. However, these parameters are generated by an external secret key of variable length (maximum 128-bits) and used in our algorithm. The encryption of each block of plaintext has been made dependent on the secret key and the cryptosystem is further made robust against any reasonable attack by using the feedback technique. Simulation results show that the proposed cryptosystem requires less time to encrypt the plaintext as compared to the existing chaotic cryptosystems and further produces the ciphertext having flat distribution of same size as the plaintext.

A Random Bit Generator Using Chaotic Maps

Chaotic systems have many interesting features such as sensitivity on initial condition and system parameter, ergodicity and mixing properties. In this paper, we exploit these interesting properties of chaotic systems to design a random bit generator, called CCCBG, in which two chaotic systems are cross-coupled with each other. To evaluate the randomness of the bit streams generated by the CCCBG, the four basic tests: monobit test, serial test, auto-correlation, Poker test and the most stringent tests of randomness: the NIST suite tests have been performed. As a result no patterns have been observed in the bit streams generated by the proposed CCCBG. The proposed CCCBG can be used in many applications requiring random binary sequences and also in the design of secure cryptosystems.

Diffusion-substitution based gray image encryption scheme

In this paper, an encryption algorithm for gray images using a secret key of 128-bits size is proposed. Initially, visual quality of image is degraded by the mixing process. Resultant image is partitioned into key dependent dynamic blocks and, further, these blocks are passed through key dependent diffusion and substitution processes. Total sixteen rounds are used in the encryption algorithm. Proposed technique is simple to implement and has high encryption rate. Simulation experiment results have been given to validate the high security features and effectiveness of proposed system.

Suppression of chaos using mutual coupling

We demonstrate in this communication the suppression of chaos in a chaotic oscillator by establishing mutual coupling with an another weak periodic oscillator of the same kind. We have chosen specific locations of the state variable for the mutual coupling and the suppression of chaos is observed via period halving route as a result of increase in mutual coupling strength between the oscillators. The technique developed does not require any prior knowledge of the system dynamics and the system parameters are not changed explicitly. The method is expected to be useful for those physical chaotic systems in which direct accessibility of its parameters is either difficult or not possible.

Medical image protection using genetic algorithm operations

The security of digital medical images has attracted much attention recently, especially when these images are sent through the communication networks. An image encryption technique tries to convert an image to another image that is hard to understand. In this communication, we propose an encryption method for gray scale medical images based on the features of genetic algorithms. Performance analysis show that the proposed scheme has good statistical character, key sensitivity and can resist brute-force attack, differential attack, plaintext attack and entropy attack efficiently.

Image Encryption through a Novel Permutation-Substitution Scheme Based on Chaotic Standard Map

A novel permutation-substitution scheme, which is based on chaotic standard map, for the image encryption is proposed. It is loss-less symmetric block cipher and specifically designed for the colour images. The initial condition & system parameter of the chaotic standard map, number of iterations and number of rounds constitute the secret key of the algorithm. Firstly we mix all three colour layers (3 D matrix) of the plain image and convert them into a 2D matrix. Each encryption round comprises of three stages: permutation rounds, substitution rounds and again permutation rounds. To increase the speed of encryption, the permutation and substitution are done row-by-row and column-by-column instead of pixel-by-pixel. The permutation process is controlled through the pseudo random number sequences (PRNS) generated from the discretization of chaotic standard map, however in the substitution, the properties of rows and column pixels of various layers are mixed with the PRNS generated from the standard map. The security of the proposed image encryption has been analyzed thoroughly using various statistical analysis, key sensitivity analysis, differential analysis, key space analysis, etc. Results suggest that the proposed image encryption technique can be used for the real time secure image and video communication applications.

(e, 2e) triple differential cross sections of Ca atoms at low energies

Recently, several theoretical studies (Hitawala et al 2008 J. Phys. B: At. Mol. Opt. Phys. 41 035205; Khajuria and Deshmukh 2008 Phys. Rev. A 78 024702; Chauhan et al 2005 Phys. Rev. A 71 032708) have been reported to analyze the measurements of triple differential cross section (TDCS) for (e, 2e) processes on Ca (4s2) atom in coplanar geometry (Murray 2005 Phys. Rev. A 72 062711). In this paper, the (e, 2e) TDCS of the Ca atom has been revisited with the inclusion of correlation-polarization potential and post-collision interaction in the distorted wave Born approximation formalism. We note that the present attempt significantly improves the understanding of (e, 2e) processes at low energies on Ca atom. Still there are several discrepancies between the experimental and theoretical results that require more theoretical attempts to explain them properly.

Block cipher using 1D and 2D chaotic maps

In this paper, we present a new chaotic block cipher in which a logistic map, Henon map, and secret key are used. In the proposed chaotic cipher, the confusion and diffusion are achieved respectively with the help of chain block ciphering and secret key dependent permutation boxes. Due to the excellent confusion and diffusion properties, the proposed chaotic cipher is extremely robust. The results of the statistical analysis show that the chaotic cipher posses all features needed for a secure system and useable for the security of communication system.

Bifurcation and Chaos in Periodically Forced and Nonlinearly Damped Pendulum

Abstract In this communication, we mainly focus our attention on the global dynamical behavior of forced and nonlinearly damped pendulum. We consider the nonlinear damping term proportional to the power of velocity (v|v|p−1). Analytically we obtain the threshold condition for the occurrence of homoclinic bifurcation using Melnikov technique. We carry out the bifurcation analysis to identify the route to chaos for various cases of damping (p = 1, 2 and 3) and analyze the topological shape and fractalness of phase space attractor by computing Kaplan-Yorke dimension and Correlation dimension. We identify the regions of 2D parameter space (consists of external forcing amplitude and damping coefficient) corresponding to various types of asymptotic dynamics through extensive Lyapunov exponent calculation and analyze the fragileness and globalness of chaos in the parameter space with the introduction of nonlinear damping. We also analyze the complexity of basin of attraction for all three cases (p = 1, 2 and 3) and compute the correlation dimension to quantify the fractalness of basin boundaries.