Timing for securing the biometric template transformation based on supervised learning using Double Random Phase Encoding Method

In conventional symmetric encryption, it is common for the encryption/decryption key to be reused for multiple plaintexts. This gives rise to the concept of a known-plaintext attack. In optical image encryption systems, such as double random phase encoding (DRPE), this is also the case. With optical encryption, if one knows a plaintext-ciphertext pair, one can carry out a known-plaintext attack more efficiently than a bruteforce attack, using heuristics based on phase retrieval or simulated annealing. However, it is more likely that an attacker will find an imperfect encryption/decryption key using such heuristics. Such an imperfect key will work for the known plaintext-ciphertext pair, but not an arbitrary unseen plaintext-ciphertext pair using the original key. In this paper, we illustrate the problem and attempt to characterise the increase in security it affords optical encryption.

Most of the existing selective encryption schemes are based on image processing and cannot be realized by optical structures, so their practicality is limited. Combining the optical design, a local hybrid optical encryption system based on double random phase encoding is proposed. The system proposed in this paper possesses a common aperture and dual optical path structure, which is widely used in optical design and can effectively improve the practicality of optical encryption system. First, important information and non-important information in the original image are separated by a selective beam splitter. Then light waves carrying important information enter into the 4<i>f</i> system for encryption, and light waves carrying non-important information enter into the diffraction system for encryption. Finally, part of the diffraction system ciphertext is replaced with 4<i>f</i> system ciphertext to obtain the final encrypted image. Decryption is the reverse process of encryption. First, the 4<i>f</i> system ciphertext is cut out from the final ciphertext. Then the 4<i>f</i> system ciphertext is used to restore the information replaced in the diffraction system ciphertext, thereby obtaining the complete diffraction system ciphertext. Finally, the two ciphertexts go through the reverse process of their respective systems to complete the decryption. By comparing the statistical characteristics and mean square error of the original image and the encrypted image, the effectiveness of the proposed system's encryption process is proved. By analyzing the peak signal-to-noise ratio of the original image and the decrypted image, the effectiveness of the proposed system's decryption process is proved. The sensitivity of each key of the system is analyzed to prove the security of the system. Especially the system is highly sensitive to selective encryption key, which proves the effectiveness and security of the proposed system for selective encryption. Through simulation, it is verified that the proposed system is very resistant to diffraction attacks. Even if he can obtain all the diffraction keys, the attacker still cannot obtain the selectively encrypted information. Finally, through simulation, it is verified that the proposed system has good noise resistance and crop resistance, and high robustness as well. The proposed system can realize the selective encryption through optical structure, which is safe, effective and highly robust, and thus improving the practicality of selective optical encryption system.

Double random phase encoding (DRPE) is a typical optical encryption technique, in which the cipher key is allowed to include redundancy between encryption and decryption. It has been shown that phase-only DRPE has the robust to known-plaintext attacks using a phase retrieval algorithm. In addition, it has been also shown that phase only DRPE can decrypt the encrypted image successfully with the singular key that is completely different from the encryption key. In this study, we analyzed the distribution of the key-space in the phase-only DRPE by means of calculating the Euclidean distance between the decryption key and the encryption key and counting the number of the correct decryption keys. As a result of the experiments, we confirmed that the distribution property of the correct keys in the phase-only DRPE is significantly different from the one in the conventional DRPE.

The present work is devoted to research the peculiarities of an authentication system of the technical devices with the use of an optical asymmetric holographic encryption on the basis of the Double Random Phase Encoding (DRPE). The series of the numerical experiments was performed to implement the encryption and the decryption of the initial image. The angular spectrum approach was used as a tool for the simulation of the propagation of the light in the free space forward and backward along the whole optical scheme of the DRPE. In the present work the particularities of the authentication system based on an asymmetric approach of the holographic encryption method DRPE were studied.

Full Poincaré beams, which cover all polarization states on the Poincaré sphere, provide a unique and complete degree of freedom for polarization manipulation in optical encryption. This paper introduces a novel optical image encryption method based on double random phase encoding (DRPE) system with multi-dimensional keys of full Poincaré beam. The encryption process begins by preprocessing the full Poincaré beam with a polarizer, followed by loading the image to be encrypted along this polarization direction, and finally performing encryption via the DRPE system. The scheme integrates conventional optical keys, such as wavelength, topological charge, amplitude, and phase, with the complete polarization dimension afforded by the full Poincaré beam, as well as the spatial loading dimension of the image placed behind the lens. By synergistically combining these multi-dimensional keys, the encryption system significantly expands the key space. Additionally, the dual random phase modulation capability of the DRPE system further enhances information security. This work establishes a new paradigm for high-security optical encryption.

The principle of ptychography is applied in known plain text attack on the double random phase encoding (DRPE) system. We find that with several pairs of plain texts and cipher texts, the model of attack on DRPE can be converted to the model of ptychographical imaging. Owing to the inherent merits of the ptychographical imaging, the DRPE system can be breached totally in a fast and nearly perfect way, which is unavailable for currently existing attack methods. Further, since the decryption keys can be seen as an object to be imaged from the perspective of imaging, the ptychographical technique may be a kind of new direction to further analysis of the security of other encryption systems based on double random keys.

Compared with digital methods, image hiding methods by optical ways have many advantages such as high processing speed, high parallel, high encryption dimension etc al. A novel efficient image encryption and hiding method applied by double random phase encoding technique is discussed in this paper. First, the performance of existing optical image hiding systems is analyzed; then specific statistical detection methods to the optical image hiding system are discussed; then extracting attacks to the optical image hiding system are analyzed; finally novel optical image hiding methods by technique of double random phase encoding and digital holography are given out.

A security-enhanced multiple-image encryption method is proposed based on quick response (QR) codes and modified double random phase encoding (DRPE) in the fractional Fourier transform (FrFT) domain in this paper, where each plaintext is first converted into QR code, and then each QR code is employed to generate the corresponding binary key for decryption with the help of random binary plaintext (RBP). Subsequently, the used RBP is encrypted into noise-like ciphertext by using the modified DRPE in the FrFT domain. In the modified DRPE method, the first random phase mask is activated by the initial FrFT with chaotic phase, and the wavelength of light and the fractional orders as well as the focal lengths of lenses are all used as digital keys to expand the key space. Moreover, the sensitivities of these digital keys are extremely high because the digital keys are closely mapped with the initial values of the chaotic system in the encryption process, which contributes to an extremely high security of the multiple-image encryption method. Furthermore, the high feasibility and strong robustness of the proposed security-enhanced multiple-image encryption method are also demonstrated by using computational simulations.

Amplitude based keyless optical encryption system using deep neural network

In this paper, a proposed cancellable biometric scheme is based on multiple biometric image identifiers, Arnold’s cat map and double random phase encoding (DRPE) to obtain cancellable biometric templates. The proposed segmentation scheme that is used to select the region of interest for generating cancelable templates is based on chaos entropy low correlation statistical metrics. The objective of segmentation is to reduce the computational cost and reliability of template creation. The left and right biometric (iris, fingerprint, palm print and face) are divided into non-overlapping blocks of the same dimensions. To define the region of interest (ROI), we select the block with the highest entropy. To shorten the registration process time and achieve a high level of security, we select 25% of the image volume of the biometric data. In addition, the low-cost security requirement lies in the use of selective encryption (SE) technology. The step of selecting the maximum entropy is executed on all biometric blocks. The maximum right and left multi-biometric blocks are arranged in descending order from the entropy perspective and select 50% of each biometric couple and store the single matrix. The obtained matrix is scrambled with a certain number of iterations using Arnold’s Cat Map (ACM).The obtained scrambled matrix is encrypted with the DRPE to generate the cancellable biometric templates, which are further concatenated. The simulation results display better performance of the suggested cancellable biometric system in noise scenarios using the area under the receiver operating characteristic (AROC). The strength of the suggested technique is examined with correlation, irregular deviation, maximum difference and maximum deviation. The recommended proposed approach shows that the ability to distinguish the authentic and imposter biometrics of user seven in different levels of the noise environment.

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

With the advancement of multimedia technology and coming of big data era, the size of image data is significantly increased. However, the traditional image encryption methods cannot solve the emerging problems of efficient compression. To settle with this challenge, an effective content-adaptive image compression and encryption method based on compressive sensing and double random phase encoding (DRPE) is proposed in this paper. The original image is converted to one low-frequency part and three high-frequency parts by DWT and then permutated by sorting-based chaotic sequences. Afterward, a novel measurement matrix optimization algorithm based on adaptive step size is presented to measure the high-frequency components. To enhance the security of the scheme, the DRPE, quantization, and diffusion are successively performed on the complex matrix composed of the shuffled low-frequency component and three measurement value matrices to obtain the cipher image. Logistic-Sine chaotic system is utilized to produce the chaotic keystreams for the encryption process, and its system parameter and initial value are determined by the information entropy of the plain image and external key parameters, so that the proposed cipher can withstand known-plaintext and chosen-plaintext attacks effectively. Numerical experiments demonstrate the effectiveness of the proposed image compression and encryption algorithm.

A use of liquid crystal panels (LCPs) as a random phase modulator in the optical encryption system based on the double random phase coding (DRPC) [Optics Letters, Vol.20, 767(1995)] is considered in the present paper. Required phase modulation property of LCPs as random phase modulators in the DRPC are investigated by computer simulations. It is found from simulation results that the required number of independent patches for phase modulations must be greater than 128 × 128 pixels for LCPs with the maximum phase modulation of 1.55π radians. It is also found that the required maximum phase modulation can be reduced to 1.25π radians by increasing the number of independent patches to 1024 × 1024 pixles. Experimental study using a commercially available LCP (EPSON, HTPS LCP, L3P14Y-55G00) verified partially these simulation results.

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.

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.