基于压缩感知的光学图像加密技术研究

提出了一种基于压缩感知的光学数字图像加密方案,利用压缩感知理论及特点,借助双随机相位编码技术,实现了对数字图像的多重加密。通过压缩感知使用随机测量矩阵作为密钥对原始图像加密,然后对加密图像利用Arnold变换置乱二次加密,并通过4f光学系统进行双随机相位编码再次对图像加密,从而实现了对图像的多次加密。考虑实际应用中传输过程的安全性,将加密图像融合于载体图像。在接收端,对加密图像进行解密重构。实验结果表明,该加密方案能够有效降低采样数据量,具有高稳健性,对密钥响应敏感并可以抵御较强的攻击。     

基于双随机相位编码的非线性双图像加密方法

提出了一种基于双随机相位编码技术的非线性双图像加密方法,并分析了其安全性。在该方法中,加密过程和解密过程以及加密密钥和解密密钥均不相同。加密过程具有非线性,解密过程则是线性的。将两幅待加密图像复合为复振幅图像,并利用双随机相位编码技术和切相傅里叶变换进行加密,加密过程中生成两个解密密钥,解密过程则在经典的基于4f系统的双随机相位编码系统中完成。相比经典的双随机相位加密技术和基于切相傅里叶变换的单图像加密技术,该加密方法的安全性更高,它能够抵御最近提出的基于两步振幅相位恢复算法的特定攻击。理论分析和仿真实验结果都证明了此加密方法的可行性和安全性。     

基于变形分数傅里叶变换的六重密钥图像加密

提出一种利用变形分数傅里叶变换和双随机相位编码对图像加密的方法.对要加密的图像分别进行两次变形分数傅里叶变换和两次随机相位函数调制,使加密图像的密钥由原来两重增加到六重.利用全息元件,可以用光学系统实现这种加密和解密变换.计算机模拟结果表明,只有当六重密钥都完全正确时,才能准确地重建原图像,这种六重密钥加密方法提高了图像信息的安全保密性.     

基于计算鬼成像的双密钥光学加密方案

提出了一种基于计算鬼成像(CGI)的Toeplitz矩阵和轴向距离的双密钥光学加密方案。在该方案中,只需发送一个相位掩模密钥,就可以产生多种不同的随机散斑,大大减少了密钥的传输量;在接收端采用压缩感知技术进行解密。数值仿真和实验结果表明,密钥合法用户能完全恢复物体图像,而窃听者在窃听率即使达到60%的情况下,也不能获得图像的任何信息。双密钥的使用有效地提高了方案的安全性。     

基于压缩全息和空分复用的多彩色图像加密

针对现有光学加密方法进行彩色图像加密时加密容量低、解密图像失真度高等问题,提出一种基于压缩全息和空分复用的多彩色图像加密方法.在光学加密阶段,结合改进的Mach-Zehnder干涉仪与空分复用技术,通过不同的随机相位掩膜对多幅彩色图像进行同时加密,仅需单次曝光即可得到由多幅彩色图像加密的全息图.在解密过程中,由于记录全息图的过程可建模为压缩感知过程,使用两步迭代收缩/阈值算法即可求解.实验结果表明,提出的加密系统加密容量大,解密重建图像质量高,结合压缩感知理论,有效地消除了同轴全息中平方场项对解密重建性能的影响,解密图像平均峰值信噪比仅下降约2～5dB;密钥安全性高,随机相位掩膜与传播距离均起到密钥的作用,在随机相位掩膜错误或传播距离仅偏移0.25%时,便无法解密出原始彩色图像;且对噪声与遮挡性攻击具有良好的鲁棒性,解密重建性能随噪声增大下降趋势缓慢,加密全息图80%信息受到遮挡性攻击时,仍可取得良好的解密重建结果.     

基于压缩感知及光学理论的图像信息加密

针对信息加密系统中信息安全性不理想的问题,提出一种基于压缩感知的光学图像信息加密方法.在发送端,自然图像经稀疏表示、随机投影实现图像信息加密;然后将降维后的观测值通过4F双随机相位编码光学系统进行二次加密并将其融入宿主图像,实现信息加密及隐藏.在接收端,图像信息经双随机相位编码技术解码,通过正交匹配追踪算法实现原始图像信息重构.该系统能有效降低数据传输量、减小随机相位板大小.且收发方只需按照规则生成密钥而不需传输密钥,保证了密钥的安全性.仿真结果表明:解密恢复图像质量理想,峰值信噪比为30.899 1dB,且系统能较好地抵抗裁剪、噪音污染、高通滤波、旋转等攻击,鲁棒性强,安全性高.     

一种基于迭代振幅-相位恢复算法和非线性双随机相位编码的图像加密方法

提出了一种基于迭代振幅-相位恢复算法和非线性双随机相位编码的图像加密方法。该方法利用两个公开密钥和一幅"假图像"在非线性双随机相位加密系统中生成密文,接着利用迭代非线性双随机相位编码生成两个私有密钥。待加密图像和密文作为迭代加密方法中的两个限定值。解密过程则可以在经典的基于4f系统的线性的光学双随机相位编码系统中完成。该加密方法具有迭代收敛速度快、安全性高的优点。迭代该图像加密方法能够抵御最近提出的基于改进的振幅-相位恢复算法的攻击。理论分析和仿真实验都证明了此方法的有效性和可靠性。     

基于联合变换相关器光学加密和离散余弦变换的数字水印

提出了一种以联合变换相关器和离散余弦变换为基础的数字水印方法。利用联合变换相关器光学加密系统对需要隐藏的信息进行加密,然后嵌入到宿主图像8×8分块的离散余弦变换中频系数上。与其他基于双随机相位编码的数字水印技术相比,该技术在加密阶段和解密阶段的密钥相同,省去了制作复共轭密钥的麻烦。数值仿真结果表明,这种数字水印技术具有很好的不可见性和很高的安全性,对JPEG压缩、剪切、滤波和加噪声等多种数字图像处理操作都具有很强的鲁棒性。     

基于矢量运算和副像相位掩模的遥感图像加密技术

针对遥感图像及彩色图像传输过程中的信息安全问题,提出了一种利用矢量运算和副像相位掩模对彩色遥感图像加密的方法.在加密过程中,利用光学相干叠加原理将原始图像矢量分解,并叠加到R、G、B三个通道上的两个相位板当中;然后,使用副像相位掩模在菲涅尔域中双随机相位编码对其中一个相位板加密;最后,利用两个随机矩阵的Kronecker积对编码图像进行进一步随机化处理,实现彩色遥感图像的多级加密.实验结果表明:该算法的密钥敏感度高,在强度系数小于0.04的高斯噪声攻击和统计分析攻击下具有良好的稳健性;密文能够抵御选择明文攻击,相比于传统的双随机相位编码算法具有更强的安全性.解密遥感图像的峰值信噪比和相关系数可达31.92dB和0.9888.该加密方法为大量相同尺寸遥感图像的加密提供了新的思路.     

基于相移干涉与分数傅里叶变换的纯相位图像加密

只有两步的正交相移干涉方法,只需记录两幅干涉图,不需要记录物光波和参考光波的强度信息,就可以再现没有零级像和共轭像的再现像.结合分数傅里叶变换和双随机相位编码,提出一种纯相位光学图像加密技术.解密时,只要获得正确的密钥,经过简单的计算就可以重建清晰的原始图像.模拟实验验证了它的可行性和有效性,并分析了抗裁剪和噪声的鲁棒性以及参考光强度大小对加密解密的影响.     

Novel hybrid image compression–encryption algorithm based on compressive sensing

A new hybrid image compression–encryption algorithm based on compressive sensing is proposed, which can accomplish image encryption and compression simultaneously. The partial Hadamard matrix is adopted as measurement matrix, which is controlled by chaos map. The measurement is scrambled. Compared with the methods adopting the Gaussian random matrix as measurement matrix, and those using the whole measurement matrix as key, the proposed algorithm reduces the burden of transferring key and is more practical. The proposed algorithm with sensitive keys and nice image compression ability can resist various attacks. Simulation results verify the validity and reliability of the proposed algorithm.     

Secret shared multiple-image encryption based on row scanning compressive ghost imaging and phase retrieval in the Fresnel domain

A multiple-image encryption method is proposed that is based on row scanning compressive ghost imaging, (t, n) threshold secret sharing, and phase retrieval in the Fresnel domain. In the encryption process, after wavelet transform and Arnold transform of the target image, the ciphertext matrix can be first detected using a bucket detector. Based on a (t, n) threshold secret sharing algorithm, the measurement key used in the row scanning compressive ghost imaging can be decomposed and shared into two pairs of sub-keys, which are then reconstructed using two phase-only mask (POM) keys with fixed pixel values, placed in the input plane and transform plane 2 of the phase retrieval scheme, respectively; and the other POM key in the transform plane 1 can be generated and updated by the iterative encoding of each plaintext image. In each iteration, the target image acts as the input amplitude constraint in the input plane. During decryption, each plaintext image possessing all the correct keys can be successfully decrypted by measurement key regeneration, compression algorithm reconstruction, inverse wavelet transformation, and Fresnel transformation. Theoretical analysis and numerical simulations both verify the feasibility of the proposed method.     

Optical image encryption technique based on compressed sensing and Arnold transformation

A new optical image encryption method based on compressed sensing and Arnold transformation is proposed. First, dimensional reduction and random projection, the characteristics of compressed sensing, are utilized to compress and encrypt a digital image. Second, Arnold transformation is used to scramble the encryption image followed by compressed sensing with low data volume. Then, the encryption image is encrypted again by double random phase encoding optical encryption technique; two random phase masks generated by sequences of irrational number are been used as secret keys. In the end, the multi-encrypted information is embedded into the host image and transmitted. At the receiver, original image information is reconstructed approximately via orthogonal matching pursuit algorithm. The peak signal-to-noise ratio and the normalized cross-correlation between the original image and the decrypted one are used to calculate the quality of the decryption image. The experimental results demonstrate that our method is secure and robust.     

Attack on double-random-phase-encoding-based image hiding method

The double-random phase-encoding (DRPE) technique is a typical optical image encryption technique, which can also be used for image hiding. Usually, the secret image is encrypted with the DRPE technique and the encoded image is hidden into the host image via superimposition to obtain the stego-image. The attack technique on the DRPE-based image hiding method was proposed in this paper. Firstly, a randomly selected superimposition coefficient was used to approximate the original superimposition coefficient to extract the hidden encoded images from the stego-images approximately. Then, the chosen-plaintext attack technique on the DRPE-based optical image encryption technique was applied to recover the random phase masks used in the DRPE technique. The theoretical analysis indicated that, without considering the computational error, the recovered secret image via the proposed attack technique is identical to the original one. Even considering the computational error, it is identical to the secret image recovered with the original DRPE-based image hiding method, which demonstrates that the attack on the DRPE-based image hiding method is successfully achieved. The numerical simulation results demonstrated the correctness of the theoretical analysis.     

Multiple-image encryption by two-step phase-shifting interferometry and spatial multiplexing of smooth compressed signal

A multiple-image encryption method based on two-step phase-shifting interferometry(PSI) and spatial multiplexing of a smooth compressed signal is proposed. In the encoding and encryption process, with the help of four index matrices to store original pixel positions, all the pixels of four secret images are firstly reordered in an ascending order; then, the four reordered images are transformed by five-order Haar wavelet transform and performed sparseness operation. After Arnold transform and pixels sampling operation, one combined image can be grouped with the aid of compressive sensing(CS)and spatial multiplexing techniques. Finally, putting the combined image at the input plane of the PSI encryption scheme,only two interferograms ciphertexts can be obtained. During the decoding and decryption, utilizing all the secret key groups and index matrices keys, all the original secret images can be successfully decrypted by a wave-front retrieval algorithm of two-step PSI, spatial de-multiplexing, inverse Arnold transform, inverse discrete wavelet transform, and pixels reordering operation.     

Image encryption using exclusive-OR with DNA complementary rules and double random phase encoding

We propose an optical image encryption scheme based on the Deoxyribonucleic Acid (DNA) theory and the double random phase encoding (DRPE) technique. The piecewise linear chaotic map (PWLCM) is used to generate key images and random phase masks, and to determine DNA encoding rules. In order to achieve ultra-fast DNA encryption, we propose using an optical exclusive-OR (XOR) gate to achieve XOR operation in DNA encryption. Different plaintexts use different initial values of PWLCM, which are generated by Message Digest Algorithm 5 (MD5). The plaintext is encrypted by two rounds of DNA and then by DRPE to form a ciphertext. Numerical simulation and the analysis of attacks on encrypted image are implemented to demonstrate the security and validity of the proposed approach.     

Encryption by using matrix-added, or matrix-multiplied input images placed in the input plane of a double random phase encoding geometry

In this paper, we describe image encryption by combining the images with several matrices made with letters/numerals and placed in the input plane of a double random phase encoding (DRPE) system. Addition or multiplication of several such matrices with an input image provides a modified image pattern which is encrypted in a DRPE system utilizing the 4-f geometry. For gray scale images, the results of encryption in case of addition of matrices are found more reliable and secure as compared to the results of multiplication. Simulation results are presented in support of the idea. Reliability of the technique has been established by evaluating the mean square-error (MSE) between the decrypted and the original image.     

Linear exchanging operation and random phase encoding in gyrator transform domain for double image encryption

We present an optical method for double image encryption by using linear exchanging operation and double random phase encoding (DRPE) in the gyrator transform (GT) domain. In the linear exchanging operation, two primitive images are linearly recombined via a random orthogonal transform matrix. The resultant blended images are employed to constitute a complex-valued image, which is then encoded into a noise-like encrypted image by a DRPE structure in the GT domain. One can recover the primitive images exactly with all decryption keys correctly applied, including the transform orders, the random phase masks and random angle function used for linear exchanging operation. Computer simulations have been given to demonstrate that the proposed scheme eliminates the difference in key spaces between the phase-based image and the amplitude-based image encountered in the previous schemes. Moreover, our scheme has considerably high security level and certain robustness against data loss and noise disturbance.     

Securing image information using double random phase encoding and parallel compressive sensing with updated sampling processes

Recently, a new kind of image encryption approach using compressive sensing (CS) and double random phase encoding has received much attention due to the advantages such as compressibility and robustness. However, this approach is found to be vulnerable to chosen plaintext attack (CPA) if the CS measurement matrix is re-used. Therefore, designing an efficient measurement matrix updating mechanism that ensures resistance to CPA is of practical significance. In this paper, we provide a novel solution to update the CS measurement matrix by altering the secret sparse basis with the help of counter mode operation. Particularly, the secret sparse basis is implemented by a reality-preserving fractional cosine transform matrix. Compared with the conventional CS-based cryptosystem that totally generates all the random entries of measurement matrix, our scheme owns efficiency superiority while guaranteeing resistance to CPA. Experimental and analysis results show that the proposed scheme has a good security performance and has robustness against noise and occlusion.     

Secure orthogonal time-frequency multiplexing with two-dimensional encryption for optical-wireless communications

This paper firstly, to the best of our knowledge, proposed two-dimensional(2D) encryption based on the Arnold transformation for implementing a secure DC-biased optical orthogonal time-frequency multiplexing(DCO-OTFM) in optical-wireless communications(OWCs). The encrypted data is transformed to the particular 2D matrix and decrypted by the only key to get the correct information. Meanwhile, the number of keys in 2D encryption is enormous, which prevents eavesdroppers from exhaustively searching secret keys rapidly to find the right decryption. Numerical results demonstrate that the secure DCO-OTFM based on 2D encryption can effectively prevent signal decryption from the eavesdropper, which has good secure performance for applying in OWC.