Optical encryption scheme for multiple-image based on spatially angular multiplexing and computer generated hologram

A novel optical double-image encryption scheme based on Gaussian apertured reality-preserving fractional Mellin transform (GARPFrMT) is proposed. In terms of optical image encryption, GARPFrMT has several attractive advantages: (1) The GAPRFrMT can be used to scramble the value of two images simultaneously; (2) GARPFrMT is constructed in diffraction domain to ensure that the ciphertext is real; (3) Owing to the nonlinearity, this transform can ensure that the proposed encryption system can be kept from the potential insecurity; and (4) A Gaussian lens is applied to improve intensity distributions of the output light. Experimental results demonstrate that the proposed algorithm is feasible and robust by a lot of attack analysis, i.e. sensitivity attack analysis (>99.60%), differential attack analysis (NPCR >99.6072 and UACI >33.5681%), entropy values (almost 7.99928), statistical attack (correlation coefficient values are almost 0), noise attack, cropping attack and NIST analysis.

Most of existing optical color image encryption schemes have born security risks due to the adoption of linear transform, and data redundancy for the generation of complex image. To settle these problems effectively, a self-adaptive scheme for double color-image encryption is proposed in this paper. In this scheme, each RGB color component of two secret color images is first compressed and encrypted by 2D compressive sensing (CS) in which measurement matrices are generated by compound chaotic systems. Then, the two measured images are regarded as the real part and imaginary part, constituting a complex image to reduce data redundancy caused by following optical encryption. In the end, the complex image is reencrypted by self-adaptive random phase encoding and discrete fractional random transform (DFrRT) to obtain the final encrypted data. In the process of DFrRT and random phase encoding, the correlations between R, G, B components are adequately utilized. The production of key streams not only depends on the initial value but also on plain-text, and the three color components affect each other to enhance the ability against the known plaintext attack. The projection neural network algorithm is adopted to obtain the decryption images. Simulation results also verify the validity and security of the proposed method.

High-efficiency optical image authentication scheme based on ghost imaging and block processing

Intensive studies have been done to get robust encryption algorithms. Due to the importance of image information, optical encryption has played a vital role in information security. Many optical encryption schemes have been proposed but most of them suffer from poor robustness. In this paper six proposed algorithms will be presented for optical encryption to be robust to severe attacks: composite attack. Three of these approaches are based on one level Discrete Wavelet Transform (DWT) and the others are based on Wavelet Packet (WP). Not only will new techniques be presented but also a new proposed chaotic map has been developed as random keys for all algorithms. After extensive comparative study with some traditional techniques, it has been found that the novel algorithms have achieved better performance versus conventional ones. Also it has been found that WP based algorithms have achieved better performance than DWT based ones against severe composite attacks.

A hybrid digital watermarking and encryption technique based on the Computer Generated Holography (CGH) and fractional Fourier transform (FRFT) combined with singular value decomposition (SVD) algorithm is proposed for securing three-dimensional (3D) information. Initially, hierarchical 3D information is encrypted using the angular spectrum diffraction method and a random phase key. This process yields a binary real valued CGH, where incorporating a random phase key broadens the key space and adds complexity, effectively scrambling and concealing the 3D information. Subsequently, the encrypted binary real valued CGH is embedded into the host image as a watermark using the FRFT-SVD algorithm. This hybrid approach enhances the security of the watermarking process. In the final step, the CGH watermark is extracted using the inverse operation of the embedding algorithm. Applying the correct optical key and angular spectrum inverse algorithm successfully reconstructs the 3D information. The watermark algorithm’s efficiency significantly improves by leveraging the rapid computational speed and high focusing capabilities of the FRFT. Additionally, integrating SVD enhances the image’s resistance to geometric attacks, thereby improving the algorithm’s invisibility and robustness. The proposed scheme effectively achieves the encryption and digital watermarking of 3D information. Simulation results substantiate the presented watermarking scheme’s efficacy and robustness.

The diffraction efficiency, defined as the ratio of diffracted power to incident power, is one of the key working indicators for a computer-generated hologram (CGH). The CGH with high diffraction efficiency could suppress stray light and eliminate ghost images, thus improving interferometric performance in aspherical testing of low-reflectivity or large off-axis distance surfaces. However, the high-efficiency CGH is hard to precisely fabricate by traditional reactive ion etching and focusing ion beam, because it requires high etching depth with a high uniformity and sub-nanometric roughness in the glass, especially in the fabrication of a large CGH with an aperture of up to 300 mm. In this study, fabrication of the above-mentioned CGH was demonstrated via what we believe to be a new method called scanning homogenization etching (SHE), in which the ion source with a Gaussian energy distribution accurately scans the glass surface to realize homogenization etching. Different from controlling dwell time at each etching point, this paper proposes to control the scanning rate to achieve not only uniform but also quantitative depth removal in a single scan. Moreover, the depth errors in deep etching across the whole glass surface can be remarkably reduced due to homogenization effects introduced by multiple scanning etching. Finally, the target etching depth of 692.3 nm with an etching uniformity of 2.2% in the etching of a 300 mm CGH was achieved. The roughness of the etched and unetched area both have Ra values of 0.3 nm. The diffraction efficiency of working order is 39.998%, achieving 98.6% of the theoretical diffraction efficiency. In addition, the SHE is not limited by the aperture of the ion source, so it can achieve even larger diffractive optical elements with high diffraction efficiency and high accuracy.

Scanning ion beam etching: A method for the fabrication of computer-generated hologram with nanometric accuracy for aspherical testing

With the rapid development of computer network technology, information security has attracted increasing attention. Due to the characteristics of multi-dimensional operation and parallel processing capability, optical image encryption techniques have been receiving more and more attention. Since the well-known double random phase encoding technique was proposed, many other methods based on optical information processing means such as the use of optical transform, interference, and polarized light encoding, have been proposed for optical image encryption. However, recent researches have demonstrated that traditional optical encryption techniques are symmetric cryptosystems, in which decryption keys are identical to encryption keys and they have been found to be vulnerable to different types of attacks, such as known plaintext and chosen plaintext attacks. To overcome this shortcoming, asymmetric cryptosystems based on nonlinear phase-truncation techniques and phase retrieval algorithm have been proposed. Asymmetric cryptosystem is a cryptographic system in which encryption keys are different from decryption keys. The encryption keys are used as public keys which are disseminated widely, and the decryption keys are used as private keys which are known only to the authorized users. So, asymmetric cryptosystem can offer a higher-level security than symmetric cryptosystem. However, asymmetric cryptosystems based on phase retrieval algorithms require a lot of computational time, and asymmetric cryptosystems based on phase-truncated Fourier transforms have been found to be vulnerable to special attack. Therefore, in this paper, a novel asymmetric image encryption method is proposed by using the gyrator transform and vector operation. The original image is encrypted into two phase masks with vector operation. One is a random phase mask and the other is a phase mask related to the original image. In the encryption process, the random phase mask is used as a phase key and the other phase mask is transformed by gyrator transform. The transform result is performed by Fourier transform after being modulated by a phase distribution. The ciphertext is the amplitude of the above result. Compared with previous encryption schemes, the suggested method has two advantages. Firstly, we have proposed a new asymmetric encryption method based on the gyrator transform and vector operation. The decryption process is different from the encryption process. The gyrator transform and Fourier transform are used in the encryption process, while only the inverse operation of Fourier transform is employed in the decryption process. In addition, the decryption keys produced in the encryption process are different from the encryption keys. Therefore, the proposed scheme has high resistance against the conventional attacks. Secondly, the encrypted result is real-valued, which is convenient for display, transmission and storage.Numerical simulations illustrate the feasibility and effectiveness of the proposed encryption scheme.

Metasurface‐enabled full‐polarization vectorial holography has attracted numerous attention due to the promising applications for multichannel displays, enhanced information capacity, and optical encryption. However, recently showcased design strategies suffer from undesirable cross‐talk resulting from interleaved meta‐atoms and are restricted to a two‐dimensional plane. This work presents a general approach for full‐polarization beam shaping in three‐dimensional space by completely exploiting the capacity of a noninterleaved metasurface. The noninterleaved metasurface is spin‐decoupled, which is capable of achieving independent phase control for the two orthogonal circular polarizations by combining both propagation and geometric phases. As a proof‐of‐concept, a three‐dimensional vectorial holography capable of converting the linear polarized light to holographic images with arbitrary spatial polarization distributions is experimentally demonstrated. Taking use of the extended dimension, the z‐axis distance, which provides a new degree of flexibility for boosting information capacity and security, a double‐level optical encryption scheme is implemented. This work provides a compact and general scheme for full‐polarization channel wavefront steering, unlocking a new door for designing planar polarization functionality devices.

Double optical image encryption using discrete Chirikov standard map and chaos-based fractional random transform

Optical encryption of information using Computer Generated Holograms (CGH) is a well-known discipline based on the modification of the phase pattern obtained from the calculation of the hologram from a scene. This paper presents an evolution of this technique adding random pixel permutation. The complete workflow is described starting from the synthesis of a 3D scene by Computer Graphics, its storage in a CGH, the encryption and decryption process, showing results obtained in the laboratory and by simulation. Special emphasis is given to the proposals related to the encryption phase, allowing the use, if desired, of a single key in the pixel permutation and phase modification processes to generate the encrypted CGH. The similarity between different encryption levels is used as a metric to evaluate the results obtained.

Optical color image encryption based on computer generated hologram and chaotic theory

We present a simple and fast calculation algorithm for a computer-generated hologram (CGH) by use of wavefront recording plane. The wavefront recording plane is placed between the object data and a CGH. When the wavefront recording plane is placed close to the object, the object light passes through a small region on the wave recording plane. The computational complexity for the object light is very small. We can obtain a CGH to execute diffraction calculation from the wavefront recording plane to the CGH. The computational complexity is constant. The total computational complexity is dramatically reduced in comparison with conventional CGH calculations.

It is known that chaotic, especially hyperchaotic system can be suitable for the application in image encryption owing to itself characteristics. While currently, certain improved chaotic or hyperchaotic systems are confronted with the security issue of encryption due to their less complex dynamical behaviors. To address the problem well, we introduce a novel two-dimensional (2D) crossed hyperchaotic map which is based on the logistic map and the infinite collapse map. The analysis of phase diagram and Lyapunov exponential spectrum demonstrate that the given system can exhibit extensive hyperchaotic behavior and good traversal properties. Moreover, the growing use of digital images has prompted demand for multi-image encryption scheme. For this reason, based on the given 2D crossed hyperchaotic map, a multiple image encryption (MIE) scheme that employs a cross-plane with the operation of simultaneous permutation and diffusion to modify the values of its positions and pixels across multiple images is proposed. A pixel blur preprocessing technique is introduced such that the efficiency of key calculation and the speed and safety of information encryption are greatly improved. Eventually, some simulation examples and security analysis reveal that the put forward encryption scheme is able to keep out kinds of attacks such as the selective plaintext attacks and data loss.

The paper presents an opto-double color image cipher using two dimensional (2D) chaotic Arnold transform (AT) as a preprocessing scrambling stage and 2D chaotic Logistic adjusted Sine map (LASM) phase masks in the Fresnel (Fr)-based Hartley Transform (HT). In the proposed opto-double color image cipher, the 2D chaotic LASM is utilized to create chaotic phase masks. The color plainimage red, green and blue channels are firstly scrambled with 2D chaotic AT. Then, the scrambled color plainimage red, green and blue R-G-B channels are modulated using the 2D chaotic LASM phase mask and transformed with the Fr-based HT. The transformed complex R-G-B channels distributions are secondly scrambled with the 2D chaotic AT, modulated secondly with the 2D chaotic LASM phase mask and transformed with Fr-based HT. The utilization of 2D chaotic LASM phase masks in addition to the 2D chaotic AT provides efficient key administration and communication. Also, optical geometric parameters are considered as extra additional keys that enhances the secrecy of the proposed scheme. A comprehensive security study is employed for the proposed scheme and test results verifies and ensures that the proposed scheme is highly immune and resistant against most potential attacks.