双随机相位编码光学加密系统的唯密文攻击

针对双随机相位编码光学加密系统的安全性分析表明，该系统属于线性对称分组密码系统，其线性性质为安全性留下极大隐患.在唯密文攻击下，仅根据密文估计出物面波函数的“支撑”(support)，然后利用迭代相位恢复算法获得物面波函数(其振幅是明文信息)，再根据物面波函数与频域密文的关系可推导出频谱平面的解密密钥.由于估计出来的物面波函数的“支撑”相对于真实的物面波函数的“支撑”有一定的平移，使得恢复的物面波函数与真实的物面波函数之间无论在振幅上还是相位上都存在平移，导致用推导出来的解密密钥去解密其他密文时所获得的明文与原始明文之间存在明显平移.然而，可依照这一先验信息，将估计出来的物面波函数的“支撑”在物面内遍历，从而找到逼近真实解密密钥的解.利用此解密密钥去解密其他密文时获得更好的解密效果. 关键词： 光学信息安全 双随机相位编码 唯密文攻击 函数支撑     

On the security of a class of discrete-time chaotic cryptosystems

In this Letter we analyze the security of some recently proposed chaotic cryptosystems and give methods to break the cipher to reveal the encrypted information. The method exploits the dependencies between the parameters and the output sequence of a dynamical system to reveal the secretly shared system parameters. For each encryption scheme a known plaintext attack and a ciphertext only attack are given.     

Comments on “Color image encryption using Choquet fuzzy integral and hyper chaotic system”

An image encryption system whose cipher code stream only controlled by the secret key, but has nothing to do with the plaintext, is vulnerable to chosen plaintext attacks. Recently, an image encryption scheme using Choquet fuzzy integral and hyper chaotic Lorenz system has been proposed Liu et al. (2013), which employed plaintext-independent cipher code stream, then should be subjected to chosen plaintext attack. This paper cryptanalyzed the aforesaid encryption scheme using chosen plaintext attack, and pointed out that even if possessing good pseudorandom cipher code generation method, the encryption system is still insecure with unreasonable designed encryption scheme.     

Cryptanalysis and improvement of a digital image encryption method with chaotic map lattices

A digital image encryption scheme using chaotic map lattices has been proposed recently. In this paper, two fatal flaws of the cryptosystem are pointed out. According to these two drawbacks, cryptanalysts could recover the plaintext by applying the chosen plaintext attack. Therefore, the proposed cryptosystem is not secure enough to be used in the image transmission system. Experimental results show the feasibility of the attack. As a result, we make some improvements to the encryption scheme, which can completely resist our chosen plaintext attack.     

An enhanced sub-image encryption method

Recently a parallel sub-image encryption method is proposed by Mirzaei et al., which is based on a total shuffling and parallel encryption algorithm. In this paper, we firstly show that the method can be attacked by chosen plaintext attack and then propose an enhanced sub-image algorithm, which can completely resist the chosen plaintext attack. Moreover, our improved algorithm can reduce the encryption time dramatically. The experimental results also prove that the improved encryption algorithm is secure enough. So the improved method can be used in image transmission system.     

一种超混沌图像加密算法的安全性分析及其改进

根据Kerckhoff准则, 从选择明文攻击和选择密文攻击出发, 对一种超混沌图像加密算法进行分析,结果表明该算法密钥流与明文无关,并且一个明文字节只能影响一个密文字节,导致利用选择明文攻击和选择密文攻击能够以很小的计算代价破译密文.基于此,本文提出一种改进的超混沌图像加密算法,并进行了统计分析、差分分析、相关性分析及密钥敏感性测试.理论分析及仿真结果表明,改进算法不仅可以抵御选择明文攻击和选择密文攻击,而且具有较好的统计特性及差分特性等密码学特性. 关键词： 超混沌 选择明文攻击 选择密文攻击 Matlab分析     

An image encryption scheme based on the MLNCML system using DNA sequences

We propose a new image scheme based on the spatiotemporal chaos of the Mixed Linear–Nonlinear Coupled Map Lattices (MLNCML). This spatiotemporal chaotic system has more cryptographic features in dynamics than the system of Coupled Map Lattices (CML). In the proposed scheme, we employ the strategy of DNA computing and one time pad encryption policy, which can enhance the sensitivity to the plaintext and resist differential attack, brute-force attack, statistical attack and plaintext attack. Simulation results and theoretical analysis indicate that the proposed scheme has superior high security.     

基于菲涅耳域的双随机相位编码系统的选择明文攻击

用密码分析学的方法对菲涅耳域双随机相位加密系统进行了安全性分析，并提出了一种选择明文攻击的方法，利用多个冲击函数作为选择的明文，成功破解了菲涅耳域的双随机相位加密系统，并给出了密钥的解析式.此方法最大的优点在于解密的无损性，并从理论上加以证明，给出了模拟实验结果. 关键词： 信息光学 双随机相位加密 选择明文攻击 菲涅耳变换     

Novel image encryption algorithm based on cycle shift and chaotic system

In this paper, a novel image encryption algorithm is proposed. The cycle shift in bits of pixels and the chaotic system are employed for the encryption of the proposed scheme. For cycle shift operations, random integers with the same size of the original image are produced to scramble the plaintext image. Moreover, the scrambled image effects the initial values of the chaotic system for the further encryption process, which increases the sensitivity of plaintext images of the scheme. The scrambled image is encrypted into the ciphered image by the keys which are produced by the chaotic system. The simulation experiments and theoretical analyses indicate that the proposed scheme is superior and able to resist exhaustive attack and statistical attack.     

A self-cited pixel summation based image encryption algorithm

In this paper, a novel image encryption algorithm is presented based on self-cited pixel summation. With the classical mechanism of permutation plus diffusion, a pixel summation of the plain image is employed to make a gravity influence on the pixel positions in the permutation stage. Then, for each pixel in every step of the diffusion stage, the pixel summation calculated from the permuted image is updated. The values from a chaotic sequence generated by an intertwining logistic map are selected by this summation. Consequently, the keystreams generated in both stages are dependent on both the plain image and the permuted image. Because of the sensitivity of the chaotic map to its initial conditions and the plain-image-dependent keystreams, any tiny change in the secret key or the plain image would lead to a significantly different cipher image. As a result, the proposed encryption algorithm is immune to the known plaintext attack (KPA) and the chosen plaintext attack (CPA). Moreover, experimental simulations and security analyses show that the proposed permutation-diffusion encryption scheme can achieve a satisfactory level of security.     

基于相位恢复算法的单强度记录光学加密系统

在传统的双随机相位光学加密系统的基础上,提出一种新的单强度记录光学加密技术。在加密时,将原始图像置于4-f系统的输入平面上进行双随机相位光学加密,利用CCD等感光器件记录输出平面上的光强分布作为密文,该光学加密过程只需一次曝光,在解密时,利用相位恢复算法进行迭代计算就可以由密文恢复原始图像。由于解密过程采用数字方式,因此可以在解密过程中引入各种数字图像处理技术来抑制散斑噪声,进一步改善解密图像质量。通过一系列仿真实验,证明该光学加密系统可以实现对二值图像和灰度图像的光学加密,并且能够很好地抵御已知明文攻击、选择明文攻击等方法的攻击。理论分析和计算机仿真表明,该光学加密技术系统结构简单,实现方便,并且不易受到各种攻击,安全性较高。     

An improved method to enhance the security of double random-phase encoding in the Fresnel domain

Optical encryption technique based on double random-phase encoding in the Fresnel domain (named as FrDRPE) has been shown to be vulnerable to the chosen-plaintext attack owing to the linear property of the Fresnel transform. To negate such an attack, different phase-masks (i.e. part of the encryption keys of FrDRPE) are used in our system to encrypt different plaintexts while the number of the transmitted keys is not increased. In this case, a plurality of plaintext–ciphertext pairs corresponding to the same encryption key that are needed in the chosen-plaintext attack cannot be acquired by our improved system. Accordingly, this system can successfully resist the chosen-plaintext attack. Some numerical simulations are performed to validate the feasibility of our proposed scheme.     

基于联合菲涅耳变换相关器和矢量分解的光学加密方法研究

为提高光学图像加密系统的安全性,利用双光楔联合菲涅耳变换相关器和矢量分解设计了一种非线性光学图像加密系统。通过矢量分解将原始图像分解为两个相位模板,其中一个相位模板f1(x)放置于双光楔联合菲涅耳变换相关器物窗口实现图像加密;携带另一相位模板f2(x)信息的光束与解密系统输出的携带f1(x)信息的光束相干叠加得到解密图像。数值模拟了加密系统的加、解密过程,对于灰度图像和二值图像,当光楔楔角为1.8°和相位模板f1(x)与密钥k(x)的中心间距为18 mm时,解密图像与原始图像的相关系数分别为0.812 7和0.810 9;分析了密钥模板相位分布错误对解密效果的影响,验证了加密方法的可行性。模拟分析表明,密钥k(x)的位置和光楔楔角作为附加的密钥参量,有效扩展了加密系统密钥空间,并能抵御唯密文攻击、已知明文攻击和选择明文攻击。     

Cryptanalysis and improvement on a block cryptosystem based on iteration a chaotic map

Recently, a novel block encryption system has been proposed as an improved version of the chaotic cryptographic method based on iterating a chaotic map. In this Letter, a flaw of this cryptosystem is pointed out and a chosen plaintext attack is presented. Furthermore, a remedial improvement is suggested, which avoids the flaw while keeping all the merits of the original cryptosystem.     

Cryptanalysis of an ergodic chaotic encryption algorithm

In this paper, we present the results for the security and the possible attacks on a new symmetric key encryption algorithm based on the ergodicity property of a logistic map. After analysis, we use mathematical induction to prove that the algorithm can be attacked by a chosen plaintext attack successfully and give an example to show how to attack it. According to the cryptanalysis of the original algorithm, we improve the original algorithm, and make a brief cryptanalysis. Compared with the original algorithm, the improved algorithm is able to resist a chosen plaintext attack and retain a considerable number of advantages of the original algorithm such as encryption speed, sensitive dependence on the key, strong anti-attack capability, and so on.     

使用参考光波光学联合变换相关加密系统的选择明文攻击

证实了一种使用参考光波的光学联合相关变换加密系统对于选择明文攻击的脆弱性。在该加密系统中,通过选择一个透过率为零的特殊明文图像,记录其对应的联合功率谱,之后再通过遮挡输入面获取参考光波强度、遮挡参考光和明文获得加密密钥的傅里叶变换强度,根据获得的3幅图像,攻击者可以准确地获取加密所用的密钥,进而可以恢复出原始图像。理论分析和计算机模拟结果均证明所提攻击方法的有效性。     

Cryptanalysis on an image block encryption algorithm based on spatiotemporal chaos

An image block encryption scheme based on spatiotemporal chaos has been proposed recently.In this paper,we analyse the security weakness of the proposal.The main problem of the original scheme is that the generated keystream remains unchanged for encrypting every image.Based on the flaws,we demonstrate a chosen plaintext attack for revealing the equivalent keys with only 6 pairs of plaintext/ciphertext used.Finally,experimental results show the validity of our attack.     

Analysis and design of impulse attack free generalized joint transform correlator optical encryption scheme

We demonstrate in this paper that the generalized joint transform correlator (JTC) optical encryption method shows vulnerability to chosen-plaintext attacks. An unauthorized user, who has access to probe the encryption machine, can obtain the encryption keys with the help of the impulse function as chosen plaintext. The vulnerability of traditional joint transform correlator encryption is also analyzed in this paper. To prevent this attack, an enhanced angular multiplexing double-arm encryption solution is proposed. Cryptanalysis indicates that the improved scheme is robust to the chosen-plaintext attacks. Based on the analysis, a guideline for designing impulse attack free encryption system is discussed. Numerical simulation is also presented to show the validity of the proposed approach.     

一类改进的混沌迭代加密算法

指出了最近提出的一类混沌迭代分组密码算法的缺陷,通过选择明文攻击可以恢复出置换后的明文.算法中二进制序列的产生只依赖于密钥,而与明文无关,从而使算法容易造成信息泄露并遭受攻击.基于此,给出了一种可以抵御选择明文攻击的安全性更高的算法. 关键词： 混沌 混沌密码 攻击 安全性     

An improved image encryption algorithm based on chaotic maps

Recently, two chaotic image encryption schemes have been proposed, in which shuffling the positions and changing the grey values of image pixels are combined. This paper provides the chosen plaintext attack to recover the corresponding plaintext of a given ciphertext. Furthermore, it points out that the two schemes are not sufficiently sensitive to small changes of the plaintext. Based on the given analysis, it proposes an improved algorithm which includes two rounds of substitution and one round of permutation to strengthen the overall performance.