Digital encryption with undercover multiplexing by scaling the encoding mask

We introduce the technique to get the undercover multiplexing of a set of encrypted data. We base the general encryption approach on the double-random phase encoding method. We made the encoding phase masks with scaled versions of a master speckle pattern. A fake object is encrypted using a master mask made with the master speckle pattern. Each subsequent object to be hidden is associated to a suitable different scaled version of the original master mask. We apply the term suitable referring to avoid a possible cross-talk in the final decrypted images. All encrypted data are multiplexed to form a single message. This operation enables the true information undercover. We openly send this undercover message along with the master mask. Via separated private channels, we send the information on the actual scaling for each encrypting mask to the authorized users. Unauthorized users attempting to recover the information by using the master mask alone, get the fake object. During decryption of the multiplexed message, we only reconstruct the object that matches the predetermined scaled version of the master mask used to encode it. We show results that confirm our approach.     

Encrypted optical memory system using three-dimensional keys in the Fresnel domain

An encrypted optical memory system using double random phase codes in the Fresnel domain is proposed. In this system, two random phase codes and their positions form three-dimensional keys for encryption of images and are used as keys to recover the original data. The third dimension is the positions of the codes, which can have as many as three degrees of freedom. Original images encrypted by use of the two phase codes located in the Fresnel domain are stored holographically in a photorefractive material. We demonstrate in preliminary experiments encryption and decryption of optical memory in a LiNbO(3) :Fe photorefractive crystal by use of angular multiplexing.     

Multiplexing encryption-decryption via lateral shifting of a random phase mask

We present an holographic memory optical arrangement based on the successive shifting of a random pure-phase mask to achieve encrypted images multiplexing. The input images are encrypted to a stationary white noise using the usual double random encoding in the Fresnel domain. The encrypted information is imaged in a photorefractive crystal where also a reference beam impinges. In the holographic memory, a BSO crystal is used to provide both a recording medium and a phase conjugate mirror. The combination of these two features supplies at the same time the necessary exact cancellation of the random pure-phase mask as well as allows a real-time decryption process. Successive images are encrypted and position-encoded by speckle patterns arising from the random pure-phase mask in-plane shifting between exposures. We include experimental results to corroborate the multiplexing capability and the read-out fidelity of the proposed arrangement.     

Multiple-encoding retrieval for optical security

We propose a method for image encryption by multiple-step random phase encoding with an undercover multiplexing operation. The true image is stored in a multiple record we call encodegram; and then we can reconstruct it by the use of the appropriate random phase masks and a retrieval protocol. To increase the security of the true hidden image and confuse unauthorized receivers, we add to the encodegram an encoded fake image with different content. This fake image has only a small effect on the retrieval of the true hidden image, owing to the specific property of this protocol. In the decryption step, we can reveal the true image by applying the inverse protocol to two cyphertexts, one the encodegram containing the true image along with the fake image; and the other helping to get the random phase key to achieve the true image. Computer simulations verify the validity of this method for image encryption. Digital implementation of the method makes it particularly suitable for the remote transmission of information.     

Multiplexing encryption technique by combining random amplitude and phase masks

We propose and demonstrate an encryption-selectable undercover multiplexing. We encrypt and multiplex images for storage by means of a random phase mask common to every image, covered with random amplitude masks different for each image. In order to get a correct decryption of the encoded information, we have to use the appropriate random amplitude mask; otherwise fake information is recovered. We employ a phase conjugation scheme to generate the recovering wavefronts. We analyze and compare the different alternatives and degrees of complexity this combination of masks brings to enhance the security of optical encrypting techniques. We also include an analysis on the advantages and disadvantages this undercover multiplexing protocol offers. We present digital simulations to demonstrate the soundness of the proposal.     

Three-dimensional key in a modified joint transform correlator encryption scheme

We propose a modified encryption joint transform correlator scheme that introduces an additional random phase mask. The positions of both the conventional and the new mask are crucial for successful recovery of the original data. Although the two random phase masks are 2D, variation of their relative distance constitutes an additional dimension. Consequently by including this notion, both random phase masks act as a 3-dimensional (3D) key code increasing thereby the security with respect to the conventional JTC encryption scheme. We employ this scheme to multiplex encrypted data, displacing the encoding masks. During decryption of the multiplexed information, we only reconstruct the object that matches the correct predetermined 3D key code, i.e. that matches the random masks positions in the encryption step. We present actual experimental results, by using BSO crystal as recording medium, as well as their respective analysis.     

Multiplexing encrypted data by using polarized light

We investigate the feasibility of multiplexing, employing polarized light, a set of security encrypted data. The encryption approach is based on the double random pure-phase enciphering method. Phase conjugation operation is conducted in the reconstruction stage with the aid of a photorefractive crystal which stores the encrypted information. When storing each encrypted image, a polarization change is introduced in the system. This induces decorrelation on the speckle patterns inside the storing medium. We apply this approach for multiple image encryption. We show experimental results that confirm our approach.     

Image encryption based on extended fractional Fourier transform and digital holography technique

We present a new optical image encryption algorithm that is based on extended fractional Fourier transform (FRT) and digital holography technique. We can perform the encryption and decryption with more parameters compared with earlier similar methods in FRT domain. In the extended FRT encryption system, the input data to be encrypted is extended fractional Fourier transformed two times and random phase mask is placed at the output plane of the first extended FRT. By use of an interference with a wave from another random phase mask, the encrypted data is stored as a digital hologram. The data retrieval is operated by all-digital means. Computer simulations are presented to verify its validity and efficiency.     

Multiple image encryption using an aperture-modulated optical system

A multiple image cryptosystem based on different apertures in an optical set-up under a holographic arrangement is proposed. The system is a security architecture that uses different pupil aperture mask in the encoding lens to encrypt different images. Based on this approach multiple encryption is achieved by changing the pupil aperture arrangement of the optical system among exposures. In addition to the classical speckle phase mask, the geometrical parameters characterizing the apertures are introduced to increase the system security. Even when an illegal user steals the speckle phase mask, the system cannot be broken into without the correct pupil geometrical parameters. The experimental set-up is based on a volume photorefractive BSO crystal as storing device. Information retrieval is done via a phase conjugation operation. We also have to stress that the multiple storage under this scheme, is only possible with the help of the aperture mask. Simulation and experimental results are further introduced to verify the proposed method.     

光学图像加密中随机模板的特性比较

为比较光学图像加密中随机模板的特性,分别利用随机相位模板和随机振幅模板对几种典型的光学图像加密系统进行了光学图像加密的数值模拟和加密效果分析。模拟结果表明,将随机振幅模板用于基于光学傅里叶变换的双随机模板图像加密系统时,原始图像和加密图像的相关系数大于0.5,不能有效加密原始图。但将其用于基于菲涅耳变换全息的光学图像加密系统时,原始图像和加密图像的相关系数趋于0,可获得与使用随机相位模板时非常接近的加密效果。     

双随机相位图像加密的实值编码研究

提出了一种基于双随机相位的图像实值编码方法,该方法可应用于光学图像加密.要编码的纯相位图像分别在空间域和频域加入随机相位掩膜,其中在频域将编码范围扩大4倍,经过光学系统的变换,将生成的图像取实部作为编码图像.实值编码的图像利用与编码过程类似的方法进行解码,可以准确地重建原图像.该编译码方法简单,编码图像是一个近似随机噪声的实值图像,便于数字图像的传输与输出.     

基于gyrator变换和矢量分解的非对称图像加密方法

本文结合矢量分解和gyrator变换的数学实现得到了一种新的非对称图像加密算法,它将待加密图像先通过矢量分解加密到两块纯相位板中,然后利用从gyrator变换的数学实现中推导出来的加密算法加密其中一块相位板,获得最终的实值密文.另一块相位板作为解密密钥.算法的解密密钥不同于加密密钥,实现了非对称加密,加密过程中产生的两个私钥增大了算法的安全性.数值模拟结果验证了该算法的可行性和有效性.     

Multiple images encryption based on Fourier transform hologram

A new optical encryption method is proposed in this paper to achieve multiple images encryption. We introduce reference waves with different incident angles and random amplitude masks into a Fourier transform hologram configuration to encrypt multiple images. In the encryption procedure, different random amplitude masks (RAMs) which are placed into the reference arm vertically admit the multiplexing capability. When decrypting one of the original images, reference wave with the same incident angle as encrypting the target image is used to illuminate the encrypted hologram with the insertion of random amplitude mask whose transmissivity is reciprocal of that of the encrypting random amplitude mask in the reference arm. We also simulate and analyze the influence of partly wrong decrypting key on the decrypted results. Numerical simulation proves that the proposed encryption method is valid and of high security level.     

基于全息技术的光学加密系统实值编码

提出一种基于全息技术用于光学图像加密的实值编码方法.待编码的数字图像与一个大小相同、灰度值为零的图像组成一幅新的图像,然后与一个随机相位掩膜一起通过光学透镜作傅里叶变换,取变换结果的实部作为编码输出图像.利用全息记录的方法解码,即编码输出图像和随机相位掩膜的傅里叶变换相加通过光学透镜作傅里叶反变换,记录反变换的光强分布,再通过非线性变换或灰度变换的方法可以恢复原图像.     

Double random phase encoding method using a key code generated by affine transformation

We present a 4f optical security scheme by using a key code mask generated by an affine transformation operation. The key encrypting code produced through a pseudo-random pattern generated from a source image depends on the affine transformation parameters and the iteration number that control its random properties. This procedure offers the advantage over the conventional double random phase mask encryption technique that we do not need to send the encrypting mask itself to the authorizer user, but the set of elements that leads to the construction of the key code mask.     

基于随机相位实值编码的光学图像加密

提出了一种用于图像加密的随机相位实值编码方法,待编码的纯相位图像与一个随机相位掩膜一起作傅里叶变换,取其实部作为编码图像.已编码的图像和随机相位掩膜的傅里叶变换相加作傅里叶反变换,反变换的光强可以准确地重建原图像.该编译码方法简单,编码图像是一个实值图像,便于计算机打印或显示输出.     

Signal and reference wave dually encrypted holographic memory with shift multiplexing

We propose a secure holographic storage system with signal and reference waves dually encrypted for shift multiplexing. Two random phase masks are used to encrypt the images in the input and the Fourier planes. The reference beam is phase encoded by a fiber optic faceplate. The encrypted data is stored in a LiNbO₃:Fe crystal and decrypted during the readout process. We experimentally demonstrate encryption and decryption of multiple images and the results show high quality and good fault tolerance.     

Multiple-image hiding based on interference principle

A method for hiding multiple images into one image is presented. The method is based on interference principle and double random phase mask method. A uniform plane wave interferes with two beams of light wave carrying information of two encrypted images on an output plane. The obtained interference distribution image contains information of two encrypted images. By using frequency spectrum center shift technique, the two encrypted images can be recovered successfully. Then, the interference distribution is encoded into an index matrix through a host image. The optical encryption system parameters and the host image can all be used as encryption keys, which make encrypted image information safer. Numerical simulation indicates that the method can encrypt more information into one image and reconstruct the encryption image information successfully.     

Deterministic Phase Encoded Holographic Data Storage Using Lenticular Lens Array

This work presents a novel optical holographic encrypted data storage approach based on a phase encoding multiplexed scheme. In the proposed data storage scheme, patterns to be encrypted are stored holographically in a photorefractive LiNbO₃:Fe crystal using a lenticular lens array (LLA) sheet phase-encoded multiplexing. Experimental results reveal that rotating an LLA placed as a phase modulator in the path of the reference beam is a simple but effective method of increasing the phase addresses for holographic memory in a crystal. Combining this rotational multiplexing with two-axis rotating multiplexing provides further data storage and data encryption capacity.     

Multiplexing of encrypted data using fractal masks

In this Letter, we present to the best of our knowledge a new all-optical technique for multiple-image encryption and multiplexing, based on fractal encrypting masks. The optical architecture is a joint transform correlator. The multiplexed encrypted data are stored in a photorefractive crystal. The fractal parameters of the key can be easily tuned to lead to a multiplexing operation without cross talk effects. Experimental results that support the potential of the method are presented.