In this paper, we propose a novel input wave front modulation method to enhance the security level of a Mach-Zender interferometer-based Fourier encryption system. The input data is encoded in the two wave fronts propagated in the arms of the interferometer. Both arms contain a 4f setup, and two independent Fourier keys are used to encrypt these wave fronts. During decryption the encrypted wave fronts are propagated through the interferometer. In the case when correct Fourier keys are used for decryption, the reconstructed data page is shown by the interference pattern of the output. We propose a method to synthesize two phase modulated input images for this cryptosystem. The modulation method has a user defined phase parameter. We prove that the security level of the proposed cryptosystem can be significantly improved compared with previous solutions, by using an optimally chosen phase parameter.
In this paper, we propose a novel input wave front modulation method to enhance the security level of a Mach-Zender interferometer-based Fourier encryption system. The input data is encoded in the two wave fronts propagated in the arms of the interferometer. Both arms contain a 4f setup, and two independent Fourier keys are used to encrypt these wave fronts. During decryption the encrypted wave fronts are propagated through the interferometer. In the case when correct Fourier keys are used for decryption, the reconstructed data page is shown by the interference pattern of the output. We propose a method to synthesize two phase modulated input images for this cryptosystem. The modulation method has a user defined phase parameter. We prove that the security level of the proposed cryptosystem can be significantly improved compared with previous solutions, by using an optimally chosen phase parameter.
Our goal is to enhance the security level of a Fourier optical encryption system. Therefore we propose a Mach–Zehnder interferometer based encryption setup. The input data is organized in a binary array, and it is encoded in the two wave fronts propagated in the arms of the interferometer. Both input wave fronts are independently encrypted by Fourier systems, hence the proposed method has two encryption keys. During decryption, the encrypted wave fronts are propagated through the interferometer setup. The interference pattern of the output shows the reconstructed data in cases where the correct decryption Fourier keys are used. We propose a novel input image modulation method with a user defined phase parameter. We show that the security level of the proposed cryptosystem can be enhanced by an optimally chosen phase parameter.
In this paper, we propose an improved optical security system using three phase-encoded images and the principle of interference. This optical system based on a Mach-Zehnder interferometer consists of one phase-encoded virtual image to be encrypted and two phase-encoded images, en-crypting image and decrypting image, where every pixel in the three images has a phase value of '0'and' π '. The proposed encryption is performed by the multiplication of an encrypting image and a phase-encoded virtual image which dose not contain any information from the decrypted im-age. Therefore, even if the unauthorized users steal and analyze the encrypted image, they cannot reconstruct the required image. This virtual image protects the original image from counterfeiting and unauthorized access. The decryption of the original image is simply performed by interfering between a reference wave and a direct pixel-to-pixel mapping image of the en crypted image with a decrypting image. Computer simulations confirmed the effectiveness of the proposed optical technique for optical security applications.
In this paper, the security of a cryptosystem based on phase truncation and a designed amplitude modulator (AM) is evaluated. In the cryptosystem, an undercover AM used as an additional key is added to modulate the amplitude information of the spectrum in the Fourier plane. Compared to the conventional phase-truncated Fourier transform (PTFT)-based cryptosystem, the security of the cryptosystem is improved by increasing the number of unknown keys. However, it is found that the designed AM is irrelative to the plaintext, and one of the parameters in the designed AM contributes less to the security enhancement of the cryptosystem due to low key sensitivity. Based on the analysis, a special attack containing two iterative processes is proposed to crack the cryptosystem, in which the known-plaintext-attack-based iterative process I with a specific normalization operator is used to retrieve the designed AM and the amplitude-phase-retrieval-technique-based iterative process II is used to retrieve the corresponding plaintext from the arbitrarily given ciphertext with the help of the retrieved AM. In addition, an inherent drawback widely existing in PTFT-based cryptosystems is reported for the first time: most information of the original image could be retrieved using two correct phase keys (or only the first phase key) generated in the encryption process, even without the corresponding ciphertext in PTFT-based cryptosystems. To address this issue, a security-enhanced cryptosystem is proposed in this paper. Numerical simulation is carried out to demonstrate the effectiveness and feasibility of the proposed attack and cryptosystem.
The security strength of an interference-based optical image cryptosystem with a designed amplitude modulator (AM) is evaluated. Compared to previous improved interference-based cryptosystems in which iterative or post-processing algorithms are involved, to remove the silhouette problem, a pre-designed AM is placed at the image plane to modulate the plaintext directly, which eliminates this drawback. Moreover, the AM is used as an additional private key, which enlarges the key space and further enhances the security system. However, we have noticed that one of the designed parameters in the AM has a low key sensitivity, which is fault-tolerant and is not required for precise reconstruction. Additionally, the AM is plaintext-independent, which means that the AM can be recovered first by using a pair of chosen plaintexts and the corresponding ciphertext. Based on these findings, we propose a hybrid algorithm that includes two chosen-plaintext attacks (CPAs) and a ciphertext-only attack (COA) to break the enhanced cryptosystem. Specially, CPAs with an impulse function and an arbitrarily given plaintext are proposed to retrieve two parameters in the AM. With the retrieved AM, information on the plaintext can be recovered from the corresponding ciphertext by two kinds of COAs without any knowledge of the private keys. To the best of our knowledge, this is the first time that the interference-based cryptosystem with a designed AM has been cracked successfully, which may provide potential evidence for further security improvements. Numerical simulations are carried out to validate the feasibility of the proposed attacks.
Abstract We propose a comprehensive and efficient optical-cryptographic encryption scheme to improve the security of vulnerable optical encryption systems. Based on cryptography theory, we increase data protection using diffusion-confusion processes acting in the input and output of the optical encryption scheme. The new enhanced ciphertext has attributes of a one-way function that is easy to achieve but almost impossible to revert without the correct random phase masks used for diffusion-confusion operations. Despite the straightforward design, combining optical, cryptographic, and chaos methods increases the number of encryption–decryption keys raising two significant concerns. First, the management and transmission of several keys carry a high storage footprint, and second, it impairs the optical high-speed information processing capability. We overcome these two drawbacks by applying a new optical keystream synthesizer based on the stochastic speckle nature and a maximum entropy constraint in a forward–backward propagation algorithm. This new approach quickly replicates the necessary keystream in the encryption–decryption stations offering higher security and efficiency than other reported systems. We validate the feasibility of this proposal by synthesizing an experimental keystream and performing 24-bit data encryption–decryption. Then, we verify the security improvement of two vulnerable cryptosystems and their robustness against cryptanalysis attacks. Finally, we perform experimental encryption–decryption.
A hybrid cryptosystem is proposed, in which one image is encrypted to two interferograms with the aid of double random-phase encoding (DRPE) and two-step phase-shifting interferometry (2-PSI), then three pairs of public–private keys are utilized to encode and decode the session keys (geometrical parameters, the second random-phase mask) and interferograms. In the stage of decryption, the ciphered image can be decrypted by wavefront reconstruction, inverse Fresnel diffraction, and real amplitude normalization. This approach can successfully solve the problem of key management and dispatch, resulting in increased security strength. The feasibility of the proposed cryptosystem and its robustness against some types of attack are verified and analyzed by computer simulations.