A color information cryptosystem based on optical interference principle and spiral phase encoding is proposed. A spiral phase mask (SPM) is used instead of a conventional random phase mask because it contains multiple storing keys in a single phase mask. The color image is decomposed into RGB channels. The decomposed three RGB channels can avoid the interference of crosstalks efficiently. Each channel is encoded into an SPM and analytically generates two spiral phase-only masks (SPOMs). The two SPOMs are then phase-truncated to get two encrypted images and amplitude-truncated to produce two asymmetric phase keys. The two SPOMs and the two asymmetric phase keys can be allocated to four different authorized users. The order, the wavelength, the focal length, and the radius are construction parameters of the SPM (or third SPOM) that can also be assigned to the four other different authorized users. The proposed technique can be used for a highly secure verification system, so an unauthorized user cannot retrieve the original image if only one key out of eight keys is missing. The proposed method does not require iterative encoding or postprocessing of SPOMs to overcome inherent silhouette problems, and its optical setup alleviates stringent alignment of SOPMs. The validity and feasibility of the proposed method are supported by numerical simulation results.
A color information cryptosystem based on optical interference principle and spiral phase encoding is proposed. A spiral phase mask (SPM) is used instead of a conventional random phase mask because it contains multiple storing keys in a single phase mask. The color image is decomposed into RGB channels. The decomposed three RGB channels can avoid the interference of crosstalks efficiently. Each channel is encoded into an SPM and analytically generates two spiral phase-only masks (SPOMs). The two SPOMs are then phase-truncated to get two encrypted images and amplitude-truncated to produce two asymmetric phase keys. The two SPOMs and the two asymmetric phase keys can be allocated to four different authorized users. The order, the wavelength, the focal length, and the radius are construction parameters of the SPM (or third SPOM) that can also be assigned to the four other different authorized users. The proposed technique can be used for a highly secure verification system, so an unauthorized user cannot retrieve the original image if only one key out of eight keys is missing. The proposed method does not require iterative encoding or postprocessing of SPOMs to overcome inherent silhouette problems, and its optical setup alleviates stringent alignment of SOPMs. The validity and feasibility of the proposed method are supported by numerical simulation results.
A single channel asymmetric color image encryption scheme is proposed that uses an amplitude- and phase- truncation approach with interference of polarized wavefronts. Instead of commonly used random phase masks, wavelength-dependent structured phase masks (SPM) are used in the fractional Fourier transform domain for image encoding. The primary color components bonded with different SPMs are combined into one grayscale image using convolution. We then apply the amplitude and phase truncation to the fractional spectrum, which helps generate unique decryption keys. The encrypted image bonded with a different SPM is then encoded into a polarization selective diffractive optical element. The proposed scheme alleviates the alignment problem of interference and does not need iterative encoding and offers multiple levels of security. The effect of a special attack to the proposed asymmetric cryptosystem has been studied. To measure the effectiveness of the proposed method, we calculated the mean square error between the original and the decrypted images. The computer simulation results support the proposed idea.
A novel asymmetric color information cryptosystem based on an optical coherent superposition method and phase-truncated gyrator transform (GT) is proposed. In this proposal, an original color image is converted into three independent channels, i.e., red, green, and blue. Each channel is separated into a random phase masks (RPM) and a key phase mask (KPM) using a coherent superposition method. The KPM is a modulation of the RPM by the color channel and used as decryption key. The same RPM, which is independent of plaintext, can be chosen for different images of the same size; however, KPMs, which are related to the original color images, are different. The RPM and the KPM are independently gyrator transformed. Then two gyrator spectra are, respectively, phase truncated to obtain two encoded images and amplitude truncated to generate two asymmetric phase keys. The KPM and two phase keys provide asymmetric keys. The transformation angles of the GT give additional keys for each channel and thus offer a high-level robustness against existing attacks. The proposed optical design is free from axial movement. Numerical simulations are demonstrated to verify the flexibility and effectiveness of the proposed method.
Abstract We develop a novel method to encrypt a color image by combining enhanced optical interference with phase retrieval algorithm and linear phase color-blend (LPCB). In this method, the original color image is encoded into three phase only masks (POMs) with different Fresnel diffraction distances and one fixed random phase mask (RPM). For the decryption in an optical interference system, the three individual POMs are placed in the red, green and blue channels, respectively, and the RPM is placed in the public channel. Only if the right POMs and RPM are fixed in their positions properly, one could achieve the expected information. Compared with traditional interference based color image method, our method eliminates the silhouette problem fully. LPCB is also introduced to modulate the phase value of each pixel of the three POMs to further enhance the security. Numerical simulation results are presented to illustrate the feasibility and effectiveness of the proposed scheme.
This paper offers a security analysis of an optical image cryptosystem that integrates interference and unequal modulus decomposition (EMD). In contrast to the conventional interference-based cryptosystem, which utilizes a single phase-only mask (POM) derived from the encryption process as the private key, the enhanced cryptosystem employs two random phase masks (RPMs) and two POMs derived from the phase-reserved (PR) structure as private keys. This modification addresses the silhouette problem inherent in the conventional interference-based cryptosystem by expanding the key space, thereby enhancing security strength. However, it is determined that the RPM R 2 ( u , v ) and the POM P 2 ( x , y ) exhibited low key sensitivity, thereby limiting their impact on the security enhancement. Additionally, due to the independence from the plaintext, the RPMs employed as private keys can be recovered using a designed known-plaintext attack (KPA). Once the RPMs are recovered, the number of unknown keys is reduced to two. This enables the recovery of plaintext information from its ciphertexts via a subsequent ciphertext-only attack (COA) without any prior knowledge of the POMs. In light of these findings, a novel hybrid attack strategy, to our knowledge, is proposed, integrating four cascaded KPAs and a COA, to effectively compromise the advanced interference and EMD-based cryptosystem. To validate the feasibility and effectiveness of the proposed hybrid attack, numerical simulations have been conducted.
We propose a novel optical information encryption and authentication scheme that uses asymmetric keys generated by the phase-truncation approach and the phase-retrieval algorithm. Multiple images bonded with random phase masks are Fourier transformed, and obtained spectra are amplitude- and phase-truncated. The phase-truncated spectra are encoded into a single random intensity image using the phase-retrieval algorithm. Unlike most of the authentication schemes, in this study, only one encrypted reference image is required for verification of multiple secured images. The conventional double random phase encoding and correlation techniques are employed for authentication verification. Computer simulation results and theoretical explanation prove the effectiveness of the proposed scheme.
We propose an asymmetric optical image encryption scheme with silhouette removal by using interference and equal modulus decomposition (EMD). Plaintext is first separated into two complex value masks with the same modulus using EMD in the Fresnel transform domain. The two masks are encoded into four phase-only masks (POMs), two of which are treated as ciphertexts and other two as plaintext-dependent private keys by using the inverse Fresnel transform with different diffraction distances and interference-based encryption. Any information about the plaintext, including its silhouette, cannot be retrieved using one, two, or even three of the four POMs. Our scheme also avoids the constraint of the same modulus in EMD and eliminates the vulnerability against the iterative amplitude-phase attack and advanced iterative amplitude-phase attack. Numerical simulations were used to verify the validity and security of our proposed method.