Cryptoanalysis on the optical image cryptosystem based on interference and unequal modulus decomposition.

In this paper, the security strength of an enhanced cryptosystem based on interference and the phase-retrieval technique is evaluated. The security strength of the optical cryptosystem was improved through the phase-retrieval technique used to generate a phase-only mask (POM) as the ciphertext. Due to the complex mathematical model of the phase-retrieval technique, it seems that a silhouette problem existing in the conventional interference-based scheme was removed. However, we noted that the random phase mask (RPM) regarded as the only private key was fixed in the encryption path, which is not related to the plaintext and makes it possible to be recovered using a known-plaintext attack (KPA). Moreover, we also found that the RPM has high key sensitivity, and it should be recovered precisely to retrieve information of plaintexts during the attack. Thus, a hybrid KPA where three pairs of known plaintexts and their ciphertexts are regarded as the amplitude and phase constraints to obtain the precise estimation of the RPM is proposed. Then, with the help of the estimated private key, information of the original plaintexts encoded using the cryptosystem under study could be retrieved from an arbitrarily given ciphertext without any knowledge of the private key. Our cryptoanalysis shows that the cryptosystem based on interference and the phase-retrieval technique is vulnerable to the proposed attack, and there is a security leak in it. Numerical simulations have been carried out to demonstrate the performance of our proposed attack.

We present a novel method for optical image encryption based on a modified radial shearing interferometer (MRSI), which is generally used for wavefront reconstruction. In this method, a plaintext image is first encoded into a phase-only mask (POM) and then modulated by a random phase mask (RPM), the result is regarded as the input of the radial shearing interferometer and is divided into two coherent lights, which interfere with each other, leading to an interferogram (ciphertext). The aforementioned encryption process can be achieved digitally or optically while the decryption process can only be analytically accomplished. Numerical simulation is provided to demonstrate the validity of this method.

A simplified and efficient technique of cryptography of an image will be developed. The technique will utilize two simple rounds to apply image encryption and decryption, each round will be implemented by performing a simple rows shuffling and columns shuffling, eliminating the need for computational logical and arithmetic operations required for other techniques of image encryption. Our approach, while simplifying computational demands by eliminating complex arithmetic and logical operations, maintains robust security through the integration of dual Chaotic Logistic Map Models (CLMM) to generate highly sensitive indices keys. These indices keys control row and column shuffling, which provides a high degree of permutation and resists known-plaintext and cipher text-only attacks. The technique will require two secret indices keys, these keys will be variable in the length and the contents and they will depend on the image to be encrypted-decrypted, generation of these keys will be very easy and simple. The shuffling operations will be implemented using two secret indices keys, and by implementing couple of chaotic logistic map these keys will be produced using selected chaotic parameters values included in the private key. The technique uses a 256-bit private key, chaotic logistic maps, and high sensitivity to parameter variations to achieve "Very strong" key space entropy, with encryption throughput of 19,540 KB/s and robust performance across diverse image sizes. The generated decrypted image may become so sensitive to chosen of private key values, and any little variation in the private key through the decryption task, it will be showed as a hacking try. The proposed technique will be flexible, it will be used to process every image with any size (gray and/or color), and image changing will not require any updating in the decryption and encryption processes. The developed technique will be efficient; it will decrease both the encryption and decryption times, and it lead to accelerate the image encryption process comparing with other techniques. The study systematically utilizes specific evaluation metrics to substantiate claims regarding the quality, security, and velocity of the proposed cryptographic technique. Quality is assessed by Mean Square Error (MSE) and Peak Signal-to-Noise Ratio (PSNR) metrics

Specific attack and security enhancement to optical image cryptosystem based on two random masks and interference

A novel asymmetric multiple-image encryption method using an octonion Fresnel transform (OFST) and a two-dimensional Sine Logistic modulation map (2D-SLMM) is presented. First, a new multiple-image information processing tool termed the octonion Fresneltransform is proposed, and then an efficient method to calculate the OFST of an octonion matrix is developed. Subsequently this tool is applied to process multiple plaintext images, which are represented by octonion algebra, holistically in a vector manner. The complex amplitude, formed from the components of the OFST-transformed original images and modulated by a random phase mask (RPM), is used to derive the ciphertext image by employing an amplitude- and phase-truncation approach in the Fresnel domain. To avoid sending whole RPMs to the receiver side for decryption, a random phase mask generation method based on SLMM, in which only the initial parameters of the chaotic function are needed to generate the RPMs, is designed. To enhance security, the ciphertext and two decryption keys produced in the encryption procedure are permuted by the proposed SLMM-based scrambling method. Numerical simulations have been carried out to demonstrate the proposed scheme's validity, high security, and high resistance to various attacks.

Hiding data with simplified diffractive imaging based hybrid method

Comparable Encryption proposed by Furukawa (ESORICS 2013, CANS 2014) is a variant of order-preserving encryption (OPE) and order-revealing encryption (ORE); we cannot compare a ciphertext of v and another ciphertext of v', but we can compare a ciphertext of v and a token of b and compare a token of $b$ and another token of b'. Comparable encryption allows us to implement range and point queries while keeping the order of v's as secret as possible. Recently, Karras, Malhotra, Bhatt, Nikitin, Antyukhov, and Idreos independently re-define comparable encryption and propose two schemes, a basic one and an one, based on linear algebra~(SIGMOD 2016). The basic scheme is just comparable encryption. To hide the order revealed by tokens, they also proposed an ambiguous scheme where each ciphertext has two interpretations v and vdummy. In the context of an indexed database, this means that every encryption has two places in the database corresponding to the two interpretations, masking the correct placement in the database unless the dummy value is detectable. They assessed that their basic scheme (and ambiguous scheme upon the basic scheme) is secure against known-plaintext attacks; the adversary will require O(l) plaintext-ciphertext pairs to recover secret key, where l is a security parameter. This paper cryptanalyzes their comparable encryption schemes by using simple linear algebra. We show that a few tokens and a few plaintext-ciphertext pairs instead of O(l) pairs allow us to mount several attacks efficiently. Our attacks are summarized as follows: Attacks against the basic scheme: -A ciphertext-only attack using two tokens orders the ciphertexts correctly. -A known-plaintext attack using two tokens and two plaintexts reveals exact value of v. Attacks against the ambiguous scheme: -A ciphertext-only attack using two tokens orders the ciphertexts with a constant probability. -A known-plaintext attack using three tokens and three plaintexts reveals exact value of v.

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

An encryption system that combines compressive sensing (CS) and two‐step parallel phase shifting digital holography (PPSDH) using double random phase encoding (DRPE) is presented in this paper. The two‐step PPSDH is a linear inline holographic scheme and is much suitable for encrypting the 2D/3D information in a single exposure. The distribution of random phase mask (RPM) in the DRPE is implemented using circular harmonic key which increases the security of the encryption process. In this system, the keys used to encrypt are spatial positions of the planes, wavelength, and rotation of the circular harmonics in RPMs, and CS acts as an additional key that makes the system more secure than the conventional optical encryption methods. At the transmission end, two‐step PPSDH is applied to encrypt the object information in single hologram. The digital mirror device (DMD) is placed between the object and a single‐pixel detector for acquiring fewer hologram measurements. At the receiver end, the single digital hologram is numerically recovered by using a CS optimization problem. The original complex object field is decrypted from the CS recovered holograms by the inversion of two‐step PPSDH process with the help of the correct keys. The numerical simulations are presented for complex 2D and 3D objects to test the feasibility of the proposed encryption and decryption system. The proposed method carried out intensity and phase reconstruction of the original object field using single‐pixel compressive imaging. The computer simulation results demonstrated that the encrypted information is highly secured with the rotation of the circular harmonic key. The sensitivity of the decrypted intensity and phase images is also studied with variations of the encrypted keys. The obtained results show that the proposed encryption scheme is feasible and has better security performance and robustness.

Digital images play an important role, both in daily life applications such as satellite television, magnetic resonance imaging, computer tomography as well as in the areas of engineering, research and technology. So, image security is an important part and issue in information exchange. In this paper, we present encryption of images using discrete fractional transform techniques, discrete fractional fourier transform (DFrFT), discrete fractional cosine transform (DFrCT). These techniques uses cascaded multi stages of discrete fractional fourier transforms with a random phase mask (RPM) at each stage. In decryption, at receiver all the keys and RPM should correctly known to user. Numerical simulations are presented for sensitivity of keys and their effect on mean square error (MSE).

Experimental optical secret sharing via an iterative phase retrieval algorithm

Optical encryption has been extensively researched in the field of information security due to its characteristics of being parallel and multi-dimensionsal. However, most of the proposed multiple-image encryption systems suffer from a cross-talk problem. Here, we propose a multi-key optical encryption method based on a two-channel incoherent scattering imaging. In the encryption process, plaintexts are coded by the random phase mask (RPM) in each channel and then coupled by an incoherent superposition to form the output ciphertexts. In the decryption process, the plaintexts, keys, and ciphertexts, are treated as a system of two linear equations with two unknowns. By utilizing the principles of linear equations, the issue of cross-talk can be mathematically resolved. The proposed method enhances the security of the cryptosystem through the quantity and order of the keys. Specifically, the key space is significantly expanded by removing the requirement of uncorrected keys. This approach provides a superior method that can be easily implemented in various application scenarios.

Secret shared multiple-image encryption based on row scanning compressive ghost imaging and phase retrieval in the Fresnel domain

Based on the chaos and phase retrieval algorithm, a hierarchical multiple binary image encryption is proposed. In the encryption process, each plaintext is encrypted into a diffraction intensity pattern by two chaos-generated random phase masks (RPMs). Thereafter, the captured diffraction intensity patterns are partially selected by different binary masks and then combined together to form a single intensity pattern. The combined intensity pattern is saved as ciphertext. For decryption, an iterative phase retrieval algorithm is performed, in which a support constraint in the output plane and a median filtering operation are utilized to achieve a rapid convergence rate without a stagnation problem. The proposed scheme has a simple optical setup and large encryption capacity. In particular, it is well suited for constructing a hierarchical security system. The security and robustness of the proposal are also investigated.

In conventional interference-based optical encryption schemes, a potential cracker can retrieve partial information (silhouette) of the secret image using only one phase-only mask (POM). We resolve this drawback using a phase-blend operation and piecewise linear chaotic map (PWLCM) to further encode the POMs. One cannot recover a secret image visibly when inverse phase-blend operation and inverse chaotic permutation are not carried out with the correct decryption keys. Chaotic parameters of PWLCM, and random phase-angle function in the phase-blend operation enlarge the key space and improve the security of the proposed system greatly. Numerical simulations and optoelectronic experiments are performed to verify the effectiveness of the proposed scheme.