Chaotic image encryption based on circular substitution box and key stream buffer

A new image encryption algorithm based on spatiotemporal chaotic system is proposed, in which the circular S-box and the key stream buffer are introduced to increase the security. This algorithm is comprised of a substitution process and a diffusion process. In the substitution process, the S-box is considered as a circular sequence with a head pointer, and each image pixel is replaced with an element of S-box according to both the pixel value and the head pointer, while the head pointer varies with the previous substituted pixel. In the diffusion process, the key stream buffer is used to cache the random numbers generated by the chaotic system, and each image pixel is then enciphered by incorporating the previous cipher pixel and a random number dependently chosen from the key stream buffer. A series of experiments and security analysis results demonstrate that this new encryption algorithm is highly secure and more efficient for most of the real image encryption practices.     

An image encryption scheme based on irregularly decimated chaotic maps

An image encryption scheme provides means for securely transmitting images over public channels. In this work, we propose a robust shuffling–masking image encryption scheme based on chaotic maps. The shuffling phase permutes square blocks of bytes using a 3-dimensional chaotic cat map coupled with a zigzag scanning procedure. The masking phase then scrambles b-byte blocks of the shuffled image with combined outputs of three 1-dimensional chaotic skew tent maps, in such a way that the masking of every block is influenced by all previously masked blocks. Empirical results show that while the suggested scheme has good running speed, it generates ciphered images that exhibit (i) random-like behavior, (ii) almost flat histograms, (iii) almost no adjacent pixel correlation, (iv) information entropy close to the ideal theoretical value. Furthermore, this scheme has a large key space, strong sensitivity to the secret key, and is robust against differential attacks. On the basis of these results, this scheme can be regarded as secure and reliable scheme for use in secure communication applications.     

Cryptanalysis of an image encryption scheme with a pseudorandom permutation and its improved version

Under Kerckhoff principle, this paper discusses the security property of an image encryption scheme with a pseudorandom permutation. Some findings on the security problems of the algorithm are reported in the following: (1) If each row or column of the plain-image matrix is the same, the receiver cannot decrypt correctly. (2) Each plain-text word is correlated with single cipher-text word, but independent of other cipher-text word, which cannot meet the principles of algorithm design-diffusion and confusion. (3) If the cycle numbers β are relatively small, statistics attack can be used to reveal some visual information of any other plain-images encrypted with the same secret key. Considering the above problems, we propose an improved algorithm and then analyze its performance. Theoretical analysis and simulation results show that the improved algorithm can obtain better cryptographic properties, such as statistical characteristics, difference characteristics, and so on.     

A new color image encryption scheme based on DNA encoding and spatiotemporal chaotic system

In this paper, a new color image encryption scheme based on DNA operations and spatiotemporal chaotic system is presented. Firstly, to hide the distribution information of the plain image, we convert the plain image into three DNA matrices based on the DNA random encoding rules. Then, the DNA matrices are combined into a new matrix and is permutated by a scramble matrix generated by mixed linear-nonlinear coupled map lattices (MLNCML) system. In which, the key streams are associated with the secret keys and plain image, which can ensure our cryptosystem plain-image-dependent and improve the ability to resist known-plaintext or chosen-plaintext attacks. Thereafter, to resist statistical attacks, the scrambled matrix is decomposed into three matrices and diffused by DNA deletion-insertion operations. Finally, the three matrices are decoded based on DNA random decoding rules and recombined to three channels of the cipher image. Simulation results demonstrate that the proposed image cryptosystem has good security and can resist various potential attacks.     

A new image encryption scheme based on a chaotic function

In recent years, several methods of secure image encryption were studied and developed through chaotic processes or functions. In this paper, a new image encryption scheme based on a coupling of chaotic function and xor operator is presented. The main advantages of such a method are the abilities to produce a large key space to resist brute-force attacks, and to encrypt securely images with any entropy structure assuring indistinguishability, confusion and diffusion properties in the corresponding cipher-images. The results of several statistical analysis about randomness, sensitivity and correlation of the cipher-images show that the proposed cryptosystem is efficient and secure enough to be used for the image encryption and transmission. Moreover, the implementation of the corresponding algorithm is easy and only integers are used.     

A fast encryption algorithm of color image based on four-dimensional chaotic system

As the low complexity of low-dimensional chaotic system and the slow speed of image encryption, this paper proposes a fast encryption algorithm of color image based on four-dimensional chaotic system. Firstly, we propose a new method of designing four-dimensional chaotic system based on the classical equations of three-dimensional chaotic system, to increase the complexity and key space of the encryption algorithm. Secondly, according to the nature of color images’ pixels channel, we design a new pseudo-random sequence generator and reuse the random sequence, to improve the speed of image encryption. Finally, the methods of row-major and column-major are used to diffuse the original image and the cat map with parameter is used to scramble the image pixels, respectively, to achieve the effect of encryption. The results of simulation and security analysis show that the proposed encryption algorithm is of good performance on security, robustness and high encryption speed.     

基于物理混沌的混合图像加密系统研究

文章分析了基于物理混沌的混合图像加密系统,分析了系统加密原理,并对硬件系统和软件系统进行了设计。     

基于五维混沌系统的图像加密研究

随着计算机技术、信息技术和通讯技术等高科技技术在近年来的迅猛发展,信息加密越来越受到人们的重视,提出了基于五维混沌系统用来实现图像加密的方法,并利用迭代次数和方式作为密码,实现了图像加密和解密,为信息加密提供了一种新方法。     

Novel hyper chaotic color image encryption based on pixel and bit level scrambling with diffusion

In this paper, a novel method for symmetric image encryption using Lorenz chaotic system is proposed. The main operations performed in the proposed system are keystream generation, permutation, and diffusion. In the permutation phase, both pixel-level and bit-level scrambling are performed to achieve the double scrambling property. The pixel-level scrambling is implemented by a novel approach using two different keystreams. Also, the bit-level scrambling is realized with a novel approach using cyclic shift operation and a keystream. Thus, the double scrambling ensures higher security in the permutation process. The images are encrypted by an enhanced diffusion process using another keystream. The permutation and diffusion processes use different keystreams generated from the Lorenz system with chaotic behavior. A novel method is adopted for the keystream generation phase. The security of the proposed cryptosystem has been assessed by various evaluation metrics like sensitivity analysis on key and cipher images, information entropy analysis, occlusion attack, and diverse statistical explorations such as correlation and histogram analyses. The experimental results show the supremacy and better performance of the proposed cryptosystem compared to several state-of-the-art techniques.     

An efficient and secure cipher scheme for images confidentiality preservation

In this paper, a novel image encryption scheme based on two rounds of substitution–diffusion is proposed. Two main objectives have guided the design of this scheme: (a) robustness against the most known type of attacks (statistical, chosen/known plaintext, ciphertext-only and brute force attacks) and (b) efficiency in terms of computational complexity (i.e., execution time reduction) in order to meet recent mobiles’ applications’ requirements. First, a dynamic key, changed for every input image is generated and used as the basis to construct the substitution and diffusion processes. Then, the encryption process is performed by the transmitter based on a non-linear S-box (substitution) and a matrix multiplication (diffusion), applied on each sub-matrix of the image. At the destination side, decryption is applied in the reverse order. We have conducted several series of experiments to evaluate the effectiveness of the proposed scheme. The obtained results validated the robustness of our scheme against all considered types of attacks and showed an improvement in terms of execution time reduction compared to the recent existed image-encryption schemes.     

An image encryption algorithm based on the mixed chaotic sequence

Chaos-based algorithms are proven to have advantages in image encryption. In this paper, a new algorithm mixing Logistic map, Henon map and Lorenz system is presented. Signals from two discrete chaotic maps, Logistic map and Henon map, are mixed proportionately and sent to a continuous Lorenz system to generate a chaotic sequence. Then, by masking the image data with this sequence, the encryption is realized fast and simply. Experimental tests are carried out with detailed analysis, which demonstrates the large key space, the good sensitivity to the key, the perfect diffusion and confusion properties of this new scheme.     

A novel image encryption scheme based on a linear hyperbolic chaotic system of partial differential equations

Compared with general chaotic systems, a linear hyperbolic chaotic system of partial differential equations with nonlinear boundary conditions has larger parameter space, stronger sensitivity to initial condition and control parameter, better random-like behavior and so on, but it has not been employed in cryptography so far. Then using its significant properties, we present a new cryptosystem with coupled map lattices and time-varying delay. The proposed image encryption algorithm with permutation–diffusion architecture can overcome some drawbacks in the existing methods, because the sum of pixel value of original image is used for determining the permutation parameters and the previous cipher image information is utilized in the next diffusion. Theoretical analysis and computer experiments confirm that the new algorithm is efficient, practicable, and reliable, with high potential to be adopted for network security and secure communications.     

一种基于OFDM系统的无线图像的有效传输方法

本文提出一种基于OFDM多载波系统的无线图像传输的方法。该方法将基于FFT／IFFT变换的OFDM多载波调制与基于小波变换的SPIHT嵌入式零树编码相结合，首先将SPIHT输出码流分成若干数据块，然后根据各数据块视觉重要性的不同，给其分配相应的子信道和发送功率，使视觉重要性高的码流在较低的误比特率下进行传输，实现对视觉重要性不同的码流的不等错误保护。本文在瑞利平坦衰落信道下的仿真结果表明：在低信噪比下，采用本文提出的不等错误保护方法比等错误保护方法的峰值信噪比增益要高出15dB以上。     

On the security of a new image encryption scheme based on a chaotic function

This paper analyses the security of a recently proposed image encryption algorithm and shows a series of weaknesses that make it unusable in applications requiring medium or high levels of security. We show that the algorithm has some minor flaws, such as impractical decryption or impossibility to encrypt black images as well as a major flow, linearity, which makes it vulnerable to cryptanalysis. We present a chosen cipher text attack and show that, after the cryptanalysis, an attacker can successfully decrypt any cipher image, without knowledge of the secret key.     

A novel efficient image encryption algorithm based on affine transformation combine with linear fractional transformation

Multidimensional Systems and Signal Processing - Algebraic structures and their hardware–software implementation gain considerable attention in the field of information security and coding...     

一种对角线拉伸的混沌映射图像加密算法

利用双边对角线拉伸的思想,提出一种利用图像加密的可逆二维混沌映射.该映射由左映射和右映射2个子映射组成,通过对图像的拉伸和折叠处理,实现图像的混沌加密.左映射的过程为:首先利用图像性质,从左至右将每列的像素逐个插入到对应的每行像素之间;重复这样的过程,原始图像拉伸成为一条直线;最后,按照原始图像的大小,将这条直线折叠成为一个新的图像.右映射的方向是从左至右.映射置乱了像素的位置,过程是可逆的.推导出了映射的数学表达式,设计了密钥产生的方法,分析了图像加密算法的安全性问题,仿真验证了该图像加密算法的有效性.     

嵌入式系统的数据混沌加密算法研究

随着嵌入式系统的应用日益普及,嵌入式的数据安全问题也随之突出起来。我们经常需要一种措施来保护数据,防止被一些怀有不良用心的人所看到或者破坏。但常用的PC级别的加密算法由于计算量大,不适合用于嵌入式这种硬件条件相对较差的系统。本文介绍了一种基于混沌理论的简便加密算法,算法相对简单和多变,可满足各类复杂度的加密需要,并通过在图像加密中的应用,对该算法进行了详细的分析和测试。测试表明,该算法具有优秀的加密效果,且算法复杂度低,适合嵌入式系统级应用。     

基于仿射和复合混沌的图像自适应加密算法

基于有限整数域上的三维仿射变换和复合混沌,提出了一种新的数字图像加密算法,先置乱图像中像素的位置并根据像素坐标混合像素值,然后依次进行非线性的扩散、代换、再扩散,代换时用图像数据扰动耦合的多个混沌系统以进行自适应加密.算法如此迭代3轮,可有效地抵御选择明文攻击;密钥空间巨大,可抵御穷举攻击.其中的置乱操作可以直接作用于任意宽高比的图像,不需要进行预处理.构造的混沌系统形式简单,符合模块化设计思想,易于并行实现.     

基于五维混沌系统的信号加密研究

随着计算机技术、信息技术和通讯技术等高科技技术在近年来的迅猛发展,信息加密越来越受到人们的重视。提出了基于五维混沌系统用来实现通信加密的方法,该方法利用五维混沌源信号,对原始方波信号实现掩盖加密,利用迭代次数和混沌信号的加减手段设置密码,为信息加密提供了一种新方法。