Strategy for cryptanalysis of optical encryption in the Fresnel domain

Integrating Fresnel diffraction, multi-phase retrieval, and hyperchaos mapping for color image encryption

This study proposes a color image encryption method combining Fresnel diffraction, multi-phase retrieval, and hyperchaotic mapping in two stages. First, the color image is converted into an amplitude-type computer-generated hologram (CGH) that overlaps in the frequency domain and separates in the spatial domain. The Gerchberg-Saxton (GS) multi-phase retrieval algorithm encrypts the CGH into a meaningless ciphertext in the second stage, scrambling/diffusing it further using four random sequences generated from the Lorenz hyperchaotic system. The experiment on public color images shows that the decrypted color images are highly consistent with plaintext images. This method's key has a large space (approximately 10^∧301) and a small volume. Slight changes to the plaintext completely alter the ciphertext, and its pixel values are statistically independent, thus securing the proposed method against chosen-plaintext attacks and chosen-ciphertext attacks.

Cryptanalysis for a light-field 3D cryptosystem based on M-cGAN

Integral imaging, as an excellent light-field three-dimensional (3D) imaging technique, is considered as one of the most important technologies for 3D encryption because of its obvious advantages of high robustness, security, and computational feasibility. However, to date, there is no effective cryptanalysis technology for the light-field 3D cryptosystem. In this Letter, a cryptanalysis algorithm based on deep learning for the light-field 3D cryptosystem is presented. The 3D image can be optically retrieved by the trained network model without encryption keys. The experimental results verify the feasibility and effectiveness of our proposed method.

Chosen-plaintext attack on the double random polarization encryption

Images can be optically encrypted by random encoding in the phase, the polarization, or even the coherence of a light field. It is important for these optical encryption methods to undergo rigorous cryptanalysis. However, only phase-encoding-based encryption has been rigorously analyzed to date. In this manuscript, we demonstrate that the double random polarization encryption (DRPolE) is vulnerable to chosen-plaintext attack (CPA). We show that the keys can be retrieved if one can choose the polarization states of two plaintext images and collect the corresponding cyphertext images. Our study reveals a serious concern regarding the DRPolE that should be addressed in the design of polarization-based optical encryption methods.

Security risk of diffractive-imaging-based optical cryptosystem

The well-known diffractive-imaging-based optical cryptosystem is breached in the paper. The decryption key of the system can be easily accessed by the opponent by using a new type of powerful phase retrieval method. Our result, to our best knowledge, is the first work to show the security risk of the diffractive-image cryptosystem. Meanwhile, we provide a set of numerical simulations to demonstrate the feasibility and robustness of the presented method.

Improved method of attack on an asymmetric cryptosystem based on phase-truncated Fourier transform

We propose an improved method of attack on an asymmetric cryptosystem based on a phase-truncated Fourier transform. With the proposed method of attack, an attacker is able to access the exact decryption keys and obtain precise attack results. The method is based on a novel median-filtering phase-retrieval algorithm. Compared with existing attacks, the proposed attack has the following advantages: (1) exact information of the original image can be obtained in gray-scale and binary forms; (2) better computing efficiency; (3) more robust against noise and occlusion contaminations. Numerical simulation results show the effectiveness and robustness of the proposed method. Based on the proposed method of attack, we further propose a new cryptosystem, which not only enhances the security of the system but also does not require truncated phases.

Nonlinear optical security system based on a joint transform correlator in the Fresnel domain

A new optical security system for image encryption based on a nonlinear joint transform correlator (JTC) in the Fresnel domain (FrD) is proposed. The proposal of the encryption process is a lensless optical system that produces a real encrypted image and is a simplified version of some previous JTC-based encryption systems. We use a random complex mask as the key in the nonlinear system for the purpose of increasing the security of the encrypted image. In order to retrieve the primary image in the decryption process, a nonlinear operation has to be introduced in the encrypted function. The optical decryption process is implemented through the Fresnel transform and the fractional Fourier transform. The security system proposed in this paper preserves the shift-invariance property of the JTC-based encryption system in the Fourier domain, with respect to the lateral displacement of the key random mask in the decryption process. This system shows an improved resistance to chosen-plaintext and known-plaintext attacks, as they have been proposed in the cryptanalysis of the JTC encrypting system. Numerical simulations show the validity of this new optical security system.

Image encryption by encoding with a nonuniform optical beam in gyrator transform domains

Based on an optical gyrator transform system, an image encryption algorithm is designed and studied. An original secret image is regarded as the output intensity of the second gyrator transform. A coherent nonuniform optical beam is converted into the input of the first gyrator transform. A Gerchberg-Saxton phase retrieval algorithm is employed for obtaining the compensation phases in the first gyrator transform pair. The compensation phases are regarded as the encrypted image and key in this algorithm. The parameters of the laser beam and gyrator transform can serve as the additional key of encryption method. The decryption process of this encryption algorithm can be achieved with an optical system. Numerical simulations are performed to test the validity and capability of the encryption algorithm.