Optical image encryption based on coherent diffractive imaging using multiple wavelengths

Coherent diffractive imaging is an optical technique in which the information of an object is encoded in the diffraction intensity using a single-path wave propagation strategy. In recent years, coherent diffractive imaging has attracted much attention in many fields due to its marked advantages, such as robustness to vibration and the suitability for various wavelengths. In this paper, we propose to apply coherent diffractive imaging using multiple wavelengths for optical image encryption. A light wavelength is tuned during the encryption, and a series of diffraction intensity maps (i.e., ciphertexts) is sequentially recorded in the Fresnel domain. During image decryption, an iterative retrieval algorithm is further developed, and cryptosystem security and robustness of the proposed method are also analyzed. Numerical simulation results are presented to demonstrate feasibility and effectiveness of the proposed method.     

Optical image encryption based on interference

We proposed a novel architecture for optical image encryption based on interference. The encryption algorithm for this new method is quite simple and does not need iterative encoding. The parameters of the configuration can also serve as additional keys for encryption. Numerical simulation results demonstrate the flexibility of this new proposed method.     

Structured-illumination-based lensless diffractive imaging and its application to optical image encryption

In this paper, we propose a new method in the structured-illumination-based lensless diffractive imaging using variable grating pitches. When a phase grating pitch is sequentially changed, a series of diffraction patterns can be recorded by a charge-coupled device (CCD) camera. Subsequently, a phase retrieval algorithm with a rapid convergence rate is developed to recover a high-quality object from the recorded diffraction patterns. The proposed method is further applied to optical image encryption, and simulation results are presented to demonstrate validity of the proposed method.     

Optical image encryption based on multifractional Fourier transforms

We propose a new image encryption algorithm based on a generalized fractional Fourier transform, to which we refer as a multifractional Fourier transform. We encrypt the input image simply by performing the multifractional Fourier transform with two keys. Numerical simulation results are given to verify the algorithm, and an optical implementation setup is also suggested.     

基于不对称非标准傅里叶变换的光学图像加密

针对以往光学图像加密系统中输入面和频谱面对称性的缺点，在不增加系统元件的基础上，利用球面波照射不对称非标准傅里叶变换系统进行图像加密。通过把相位掩模置于该系统的傅里叶变换平面，利用不对称非标准傅里叶变换系统的输入面和频谱面的不对称性以及频谱面对于点光源相关参数的依赖性，克服了以前光学加密系统中输入面和频谱面的对称性所带来的安全隐患，并且获得了除相位掩模以外的另外四重密匙。理论分析和模拟实验表明：该方法不仅可行，而且多增加了几重密匙，增强了系统的安全性能。     

Optical image encryption based on two beams’ interference

We proposed a method for optical image encryption on the basis of interference theory. An optical image can be produced by the interference of two beams passed two different masks. One of the masks can only modulate the phase of the beam and another can only modulate the amplitude of the beam. The encryption method is quite simple and does not need iterative algorithm. The results of simulation coincide with our method and demonstrate the feasibility of this method.     

Optical image encryption based on the multiple-parameter fractional Fourier transform

A novel image encryption algorithm is proposed based on the multiple-parameter fractional Fourier transform, which is a generalized fractional Fourier transform, without the use of phase keys. The image is encrypted simply by performing a multiple-parameter fractional Fourier transform with four keys. Optical implementation is suggested. The method has been compared with existing methods and shows superior robustness to blind decryption.     

Optical encryption scheme based on ghost imaging with disordered speckles

An optical encryption scheme based on a ghost imaging system with disordered speckles is proposed to obtain a higher security with a small key. In the scheme, Alice produces the random speckle patterns and obtains the detection results with the help of a computational ghost imaging(CGI) system. Then Alice permutes the order of the random speckle patterns and shares the permutation sequence as a secure key to the authorized users. With the secure key, Bob could recover the object with the principle of the CGI system, whereas, the unauthorized users could not obtain any information of the object. The numerical simulations and experimental results show that the proposed scheme is feasible with a small key, simultaneously,it has a higher security. When the eavesdropping ratio(ER) is less than 40%, the eavesdropper cannot acquire any useful information. Meanwhile, the authorized users could recover completely with the secure key.     

基于分频域和菲涅耳域的光学图像加密方法

结合分数傅里叶变换及菲涅耳变换,在光学图像加密系统中分别具有多密钥性和无透镜性的优点,提出了基于分频域和菲涅耳域的光学图像加密方法。基于分数傅里叶变换的光学加密系统,引入菲涅耳变换及全息技术,使原有的加密系统在不增加光学元件的基础上提高了系统的安全性。理论分析和计算机仿真模拟证明了这种方法的可行性。     

Optical color image encryption based on Arnold transform and interference method

In this paper, we propose a novel method to encrypt a color image based on Arnold transform (ART) and interference method. A color image is decomposed into three independent channels, i.e., red, green and blue, and each channel is then encrypted into two random phase masks based on the ART and interference method. Light sources with corresponding wavelengths are used to illuminate the retrieved phase-only masks during image decryption. The influence of security parameters on decrypted images is also analyzed. Numerical simulation results are presented to illustrate the feasibility and effectiveness 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.     

Optical image encryption with Hartley transforms

We propose a new method for image encryption based on Hartley transforms that is a real transform and can be realized by spatially incoherent or coherent illumination. The proposed optical implementation is based on a Michelson-type interferometer in which the pure random intensity is distributed at the Hartley plane in encryption. Computer simulations prove it is possible. A Hartley hologram method is also given and described to resolve the sign ambiguity problem that would be encountered in image reconstruction.     

Optical image encryption with silhouette removal based on interference and phase blend processing

To completely eliminate the silhouette problem that inherently exists in the earlier interference-based encryption scheme with two phase-only masks (POMs), we propose a simple new encryption method based on optical interference of one random POM and two analytically obtained POMs. Different from the previous methods which require time-consuming iterative computation or postprocessing of the POMs for silhouette removal, our method can resolve the problem during the production of the POMs based on interference principle. Information associated with the original image is smoothed away by modulation of the random POM. Illegal deciphers cannot retrieve the primitive image using only one or two of the POMs. Incorporated with the linear phase blend operation, our method can provide higher robustness against brute force attacks. Simulation results are presented to support the validity and feasibility of our method.     

Optical color image encryption based on an asymmetric cryptosystem in the Fresnel domain

In recent years, optical color image encryption has attracted much attention in the information security field. Some approaches, such as digital holography, have been proposed to encrypt color images, but the previously proposed methods are developed based on optical symmetric cryptographic strategies. In this paper, we apply an optical asymmetric cryptosystem for the color image encryption instead of conventional symmetric cryptosystems. A phase-truncated strategy is applied in the Fresnel domain, and multiple-wavelength and indexed image methods are further employed. The security of optical asymmetric cryptosystem is also analyzed during the decryption. Numerical results are presented to demonstrate the feasibility and effectiveness of the proposed optical asymmetric cryptosystem for color image encryption.     

Optical image encryption based on binary Fourier transform computer-generated hologram and pixel scrambling technology

A new method of optical image encryption with binary Fourier transform computer-generated hologram (CGH) and pixel-scrambling technology is presented. In this method, the orders of the pixel scrambling, as well as the encrypted image, are used as the keys to decrypt the original image. Therefore, higher security is achieved. Furthermore, the encrypted image is binary, so it is easy to be fabricated and robust against noise and distortion. Computer simulation results are given to verify the feasibility of this method and its robustness against occlusion and additional noise.     

Optical multi-image encryption based on frequency shift

We present a novel multi-image encryption and decryption algorithm based on Fourier transform and fractional Fourier transforms. Lower frequency parts of the original images are selected, frequency shifted and encrypted by using double phase encoding in fractional Fourier domains. Multiple images are encrypted together into a single one. A simple optical setup is given to implement the proposed algorithm. This scheme has features of enhancement in decryption accuracy and high optical efficiency. Numerical results have been given to verify the validity and efficiency of the proposed scheme.     

Optical image encryption with redefined fractional Hartley transform

A new method for optical image encryption is introduced on the basis of two-dimensional (2-D) generalization of 1-D fractional Hartley transform that has been redefined recently in search of its inverse transform. We encrypt the image by two fractional orders and random phase codes. It has an advantage over Hartley transform, for its fractional orders can also be used as additional keys, and that, of course, strengthens image security. Only when all of these keys are correct, can the image be well decrypted. The optical realization is then proposed and computer simulations are also performed to confirm the possibility of the proposed method.     

Comment on "Optical image encryption with Hartley transforms"

We numerically demonstrate that the image encryption algorithm with intensity random filtering in the Hartley domain proposed in a recent Letter by Chen and Zhao [Opt. Lett.31, 3438 (2006)] has the problem of low security. Original image information can be visually revealed only by an inverse Hartley transform without any decryption key.     

Optical image encryption based on multichannel fractional Fourier transform and double random phase encoding technique

The optical image encryption based on multichannel fractional Fourier transform (FRT) and double random phase encoding technique is proposed. Optical principles of encoding and decoding are analyzed in detail. With this method, one can encrypt different parts of input image, respectively. The system security can be improved to some extent, not only because fractional orders and random phase masks in every channel can be set with freedom, but also because the system parameters among all channels are independent. Numerical simulation results of optical image encryption based on four channel FRT and double random phase encoding are given to verify the feasibility of the method.     

Optical image encryption using improper Hartley transforms and chaos

We propose a new method for image encryption using improper Hartley transform and chaos theory. Improper Hartley transform is a Hartley transform in which the phase between the two Fourier transforms is a fractional multiple of π/2. This fractional order is called fractional parameter and serves as a key in the image encryption and decryption process. Four types of chaos functions have been used. These functions are the logistic map, the tent map, the Kaplan-Yorke map and the Ikeda map. Random intensity masks have been generated using these chaotic functions and are called chaotic random intensity masks. The image is encrypted by using improper Hartley transform and two chaotic random intensity masks. The mean square error has been calculated. The robustness of the proposed technique in terms of blind decryption has been tested. The computer simulations are presented to verify the validity of the proposed technique.