In recent years, a large amount of work on chaos-based cryptosystems have been published. However, many of the proposed schemes fail to explain or do not possess a number of features that are fundamentally important to all kind of cryptosystems. As a result, many proposed systems are difficult to implement in practice with a reasonable degree of security. Likewise, they are seldom accompanied by a thorough security analysis. Consequently, it is difficult for other researchers and end users to evaluate their security and performance. This work is intended to provide a common framework of basic guidelines that, if followed, could benefit every new cryptosystem. The suggested guidelines address three main issues: implementation, key management and security analysis, aiming at assisting designers of new cryptosystems to present their work in a more systematic and rigorous way to fulfill some basic cryptographic requirements. Meanwhile, several recommendations are made regarding some practical aspects of analog chaos-based secure communications, such as channel noise, limited bandwith and attenuation.

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Some basic cryptographic requirements for chaos-based cryptosystems

In this paper, a fast chaos-based image encryption system with stream cipher structure is proposed. In order to achieve a fast throughput and facilitate hardware realization, 32-bit precision representation with fixed point arithmetic is assumed. The major core of the encryption system is a pseudo-random keystream generator based on a cascade of chaotic maps, serving the purpose of sequence generation and random mixing. Unlike the other existing chaos-based pseudo-random number generators, the proposed keystream generator not only achieves a very fast throughput, but also passes the statistical tests of up-to-date test suite even under quantization. The overall design of the image encryption system is to be explained while detail cryptanalysis is given and compared with some existing schemes.

A fast image encryption system based on chaotic maps with finite precision representation

When chaotic systems are realized with finite precisions in digital computers, their dynamical properties are often found to be entirely different from the original versions in the continuous setting. In the literature, there does not seem to be much work on quantitative analysis of such degradation of digitized chaos and how to reduce its negative influence on chaos-based digital systems. Focusing on 1D piecewise linear chaotic maps (PWLCM), this paper reports some findings on a new series of dynamical indicators, which can quantitatively reflect the degradation effects on a digital PWLCM realized with a fixed-point finite precision. On top of that, the paper introduces a new method for studying digital chaos from an algorithmic point of view. In addition, the theoretical results obtained in this paper should be very helpful for the consideration of reducing negative influence of dynamical degradation in real design of various digital chaotic systems. As typical examples, the proposed dynamical indicators are applied to the performance comparison of different remedies for improving dynamical degradation, cryptanalysis of digital chaotic ciphers based on 1D PWLCM, and design of chaotic pseudo-random number generators with desired characteristics.

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On the dynamical degradation of digital piecewise linear chaotic maps

The security of digital images attracts much attention recently, and many image encryption methods have been proposed. In IS-CAS2000, a new chaotic key-based algorithm (CKBA) for image encryption was proposed. This paper points out CKBA is very weak to the chosen/known-plaintext attack with only one plain-image, and its security to brute-force ciphertext-only attack is overestimated by the authors. That is to say, CKBA is not secure at all from cryptographic viewpoint. Some experiments are made to show the feasibility of the chosen/known-plaintext attack. We also discuss some remedies to the original scheme and their performance, and we find none of them can essentially improve the security of CKBA.

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Cryptanalysis of a chaotic image encryption method

Chaotic cryptology is widely investigated recently. This paper reviews the progress in this area and points out some existent problems in digital chaotic ciphers. As a comprehensive solution to these problems, a novel pseudo-random bit generator based on a couple of chaotic systems called CCS-PRBG is presented. Detailed theoretical analyses show that it has perfect cryptographic properties, and can be used to construct stream ciphers with higher security than other chaotic ciphers. Some experiments are made for confirmation. Finally, several examples of stream ciphers based on digital CCS-PRBG are given, and their security is discussed.

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Pseudo-random Bit Generator Based on Couple Chaotic Systems and Its Applications in Stream-Cipher Cryptography

The applications of digital chaotic maps in discrete-time chaotic cryptography and pseudo-random coding are widely studied recently. However, the statistical properties of digital chaotic maps are rather different from the continuous ones, which impedes the theoretical analyses of the digital chaotic ciphers and pseudo-random coding. This paper detailedly investigates the statistical properties of a class of digital piecewise linear chaotic map (PLCM), and rigorously proves some useful results. Based on the proved results, we further discuss some notable problems in chaotic cryptography and pseudo-random coding employing digital PLCM-s. Since the analytic methods proposed in this paper can essentially extended to a large number of PLCM-s, they will be valuable for the research on the performance of such maps in chaotic cryptography and pseudo-random coding.

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Statistical Properties of Digital Piecewise Linear Chaotic Maps and Their Roles in Cryptography and Pseudo-Random Coding

Pseudo-random bit generator based on couple chaotic systems and its applications in stream-cipher cryptography

A technique for extending the dynamic range of medical X-ray image that uses multi-scale image decomposition is proposed to extend the dynamic range of digital radiology equipment with either image intensifier or charge coupled device.Two images obtained at different tube voltages are decomposed by multi-scale image decomposition,and the resulting components are then recombined to reconstruct an image with extended dynamic range.Experiments show that the image processed by the technique contains 3 or more regions of interest(ROI) regions while the original image contains 2 ROI regions.Total surface dose in two exposures is 2.646×10-4 Gy/cm2 that does not cause any increase in patient dose.The technique can improve the utilization of digital radiology equipment using either image intensifier or charge couple device.

A Technique For Extending Dynamic Range of Medical X-Ray Image

An algorithm for multi-scale nonlinear X-ray chest radiography contrast enhancement based on edge(MSCE) is presented to overcome the drawback of introducing visible artifacts in conventional methods.Images are decomposed within the multi-scale decomposition architecture,and then local contrast of images is obtained based on edge information.The enhancement coefficient is calculated from image's local contrast information,and the enhanced image is then obtained.The MSCE algorithm can provide a smooth enhancement of large structures to avoid these visible artifacts,and to maintain the same detail enhancement ability.Experimental results show that the average local variance in the edge region(ALVE) decreases about 36.78% and 29.64% with almost the same detail enhancement ability comparing with the Vuylsteke and Stahl's methods,and that the proposed method can achieve better perceptual quality.

Mou Xuanqin

Papers

Pseudo-random Bit Generator Based on Couple Chaotic Systems and Its Applications in Stream-Cipher Cryptography

Statistical Properties of Digital Piecewise Linear Chaotic Maps and Their Roles in Cryptography and Pseudo-Random Coding

Pseudo-random bit generator based on couple chaotic systems and its applications in stream-cipher cryptography

A Technique For Extending Dynamic Range of Medical X-Ray Image

Nonlinear Multi-Scale Contrast Enhancement for X-Ray Chest Radiography