[Show abstract][Hide abstract] ABSTRACT: A security enhanced double random phase-amplitude encryption (DRPAE) scheme is immune against the powerful known-plaintext attack, due to the insertion of an undercover amplitude random mask at the Fourier plane in the conventional double random phase encryption (DRPE) scheme. However, DRPAE, which nullifies the high level known-plaintext attack, is found to be susceptible to a simple impulse function attack. Information about the exact distribution of the amplitude mask as well as that of the Fourier plane random phase mask is divulged from an impulse function attack. A variant form of the impulse function attack is also able to show that the DRPAE scheme is as linear as the conventional DRPE scheme. Numerical simulation results validate the effectiveness of the simple impulse attack on the DRPAE scheme.
Full-text · Article · Dec 2012 · Journal of optics
[Show abstract][Hide abstract] ABSTRACT: The security enhanced double random phase-amplitude encryption (DRPAE) scheme which has been shown to be resistant to the known plaintext attack, is found susceptible to a simple point spread function (PSF) attack, as in case of the DRPE. Analogy of the DRPAE scheme with the 4-f imaging system is utilized to search for the required PSF, and an a priori knowledge of the amplitude mask is not required. Numerical simulations validate the efficacy of our proposed attack. Existence of the linearity in the DRPAE scheme is also examined.
No preview · Article · Sep 2012 · Optics and Lasers in Engineering
[Show abstract][Hide abstract] ABSTRACT: Interference-based optical encryption schemes have an inherent silhouette problem due to the equipollent nature of the phase-only masks (POMs) generated using an analytical method. One of the earlier methods suggested that removing the problem by use of exchanging process between two masks increases the computational load. This shortcoming is overcome with a noniterative method using the jigsaw transformation (JT) in a single step, with improved security because the inverse JT of these masks, along with correct permutation keys that are necessary to decrypt the original image. The stringent alignment requirement of the POMs in two different arms during the experiment is removed with an alternative method using a single spatial light modulator. Experimental results are provided to demonstrate the decryption process with the proposed method.
[Show abstract][Hide abstract] ABSTRACT: A technique for simultaneous encryption of a color and a gray-scale image is proposed, using single-channel double random-phase encoding in the fractional Fourier domain. Prior to the encryption, the segregated red, green, and blue components of the color image and the gray-scale image are encoded into a single image after changing their bit formats. The format of the encoded image is such that it cannot be perceived by the human eye. The fractional orders of the fractional Fourier transform and two random-phase masks act as key parameters for the encryption. Performance of the scheme is verified against chosen plain-text and known plain-text attacks, respectively. The effect of noise on the performance of the proposed technique is analyzed.
No preview · Article · Apr 2011 · Optical Engineering
[Show abstract][Hide abstract] ABSTRACT: This chapter describes certain speckle coding techniques for optical and digital data security applications. It reviews various optical encryption and decryption methods. To make the optical data more secure, double random patterns may be used. In the double random phase encoding (DRPE) method, two statistically independent random phase masks are used for encryption, one in the input plane and another in the Fourier plane of a 4-f imaging setup. These have been used as a coding tool for storing data. The chapter provides the results of investigation of an encryption technique using phase image for encryption and a sandwich phase mask made by using elongated speckle patterns as the key. It also provides the results of multiplexing in optical encryption of two dimensional (2D) images using an aperture system in the Fourier plane of a DRPE system. encoding; security of data; speckle
[Show abstract][Hide abstract] ABSTRACT: In an optical image encryption system based on the interference principle, two pure phase masks are designed analytically to hide an image. These two masks are illuminated with a plane wavefront to retrieve the original image in the form of an interference pattern at the decryption plane. Replacement of the plane wavefront with convergent random illumination in the proposed scheme leads to an improvement in the security of interference based encryption. The proposed encryption scheme retains the simplicity of an interference based method, as the two pure masks are generated with an analytical method without any iterative algorithm. In addition to the free-space propagation distance and the two pure phase masks, the convergence distance and the randomized lens phase function are two new encryption parameters to enhance the system security. The robustness of this scheme against occlusion of the random phase mask of the randomized lens phase function is investigated. The feasibility of the proposed scheme is demonstrated with numerical simulation results.
No preview · Article · Sep 2010 · Journal of optics
[Show abstract][Hide abstract] ABSTRACT: A new method for image encryption using integral order radial Hilbert transform (RHT) filter in the fractional Fourier transform (FRT) domain has been proposed. The technique is implemented using the popular double random phase encoding method in the fractional Fourier domain. The random phase masks (RPMs), integral orders of the RHT, fractional orders of FRT, and indices of the Jigsaw transform (JT) have been used as keys for encryption and decryption. Simulation results have been presented and the schematic representation for optical implementation has been proposed. The mean-square-error and signal-to-noise ratio between the decrypted image and the input image have been calculated for the correct as well as incorrect orders of the RHT. Effect of occlusion and noise on the performance of the proposed scheme has also been studied. The robustness of the technique has been verified against attack using partial windows of the correct random phase masks. Similar investigations have also been carried out for the chosen-, and the known-plain-text attacks.
No preview · Article · Jul 2010 · Optics and Lasers in Engineering
[Show abstract][Hide abstract] ABSTRACT: A digital technique for multiplexing and encryption of four RGB images has been proposed using the fractional Fourier transform (FRT). The four input RGB images are first converted into their indexed image formats and subsequently multiplexed into a single image through elementary mathematical steps prior to the encryption. The encryption algorithm uses two random phase masks in the input- and the FRT domain, respectively. These random phase masks are especially designed using the input images. As the encryption is carried out through a single channel, the technique is more compact and faster as compared to the multichannel techniques. Different fractional orders, the random masks in input-, and FRT domain are the keys for decryption as well as de-multiplexing. The algorithms to implement the proposed multiplexing-, and encryption scheme are discussed, and results of digital simulation are presented. Simulation results show that the technique is free from cross-talk. The performance of the proposed technique has also been analyzed against occlusion, noise, and attacks using partial windows of the correct random phase keys. The robustness of the technique against known-, and chosen plain-text attacks has also been explained.
No preview · Article · Jun 2010 · Optics Communications
[Show abstract][Hide abstract] ABSTRACT: We propose a method for image encryption using a radial Hilbert transform (RHT) filter bank in the factional Fourier transform (FRT) domain. The filter bank comprises of multiple integral order RHT filters. The scheme is implemented using the well-known double random phase encoding technique. The random phase functions, fractional orders of the FRT, and integral orders of the multiple RHT filters forming the filter bank are used as key parameters for encryption and decryption. Simulation results have been presented to analyze the performance of the proposed scheme with respect to variation in key parameters, and the schematic for its optical implementation has been presented. Effectiveness of the scheme is also shown against the noise, occlusion and attacks using partially correct random phase keys. The effect on decryption, of rotation of the RHT filter bank as well as some of the RHT filters of the filter bank has been studied. Simulation results are also presented to exhibit the performance of the technique against reshuffling the positions of the RHT filters during the decryption. Investigations have also been carried out to analyze the proposed technique against the chosen- and the known-plain-text attacks.
No preview · Article · May 2010 · Optics and Lasers in Engineering
[Show abstract][Hide abstract] ABSTRACT: The holographic search engine based on defocused recording is investigated under rational conditions. New data page modulation coding schemes are introduced for removing the ambiguous correlation characteristics and performing a reliable data search.
[Show abstract][Hide abstract] ABSTRACT: A digital holographic information system can process complex three-dimensional (3-D) object information. We demonstrate a scheme for securing complex and 3-D information in the context of in-line digital holography. Double random phase encoding in the free-space propagation domain of light is used to secure the complex information. Encrypted in-line digital holograms are recorded using the position-phase-shifting method. The encrypted complex image at the CCD recording plane is retrieved from the real-valued digital holograms, and is used for decryption. The robustness of the method has also been studied for various securing keys used in the method against blind decryption. A layer-by-layer information retrieval from the encrypted digital hologram is also discussed. The method can also be used to secure digital complex information in a virtual optics modality using holographic principles.
No preview · Article · Mar 2010 · Optics & Laser Technology
[Show abstract][Hide abstract] ABSTRACT: The impact of primary aberrations on the optical transfer function of an optical system with a vortex phase mask has been investigated in detail. The optical transfer function of such a system becomes negative in a certain frequency range even in the absence of aberrations, a feature different from the case of an optical system in which center of the point spread function is bright.
No preview · Article · Feb 2010 · Optics & Laser Technology
[Show abstract][Hide abstract] ABSTRACT: We investigate for suitable methods that enable reliable content-addressable data search in a defocused volume holographic data storage system. Two techniques have been introduced and are shown to overcome the shortcomings of the known methods used to perform content searching in defocused holographic recording geometry. In effect, we remove the deterministic errors that result because of the presence of nonmatching database records, producing almost the same correlation scores as the true targeted correlation scores. Such deterministic errors give rise to erroneous search outcomes and reduce the speed advantage of the parallel holographic data search. We present experimental results and discuss the improvements offered by the two introduced methods in terms of storage density and measured correlation scores. Both the methods of modified-balanced and 25% sparse modulation coded data pages are found to produce good results, negating the undesired correlation characteristics.
[Show abstract][Hide abstract] ABSTRACT: Conventionally a holographic data storage system uses binary digital data as the input pages. We propose and demonstrate the use of a holographic data storage system for the purpose of invariant pattern recognition of gray-scale images. To improve the correlation accuracy for gray-scale images, we present a coding technique, phase Fourier transform (phase-FT) coding, to code a gray-scale image into a random and balanced digital binary image. In addition to the fact that a digital data page is obtained for incorporation into a holographic data storage system, this phase-FT coded image produces dc-free homogenized Fourier spectrum. This coded image can also be treated as an image for further processing, such as synthesis of distortion-invariant filters for invariant pattern recognition. A space-domain synthetic discriminant function (SDF) filter has been synthesized using these phase-FT coded images for rotation-invariant pattern recognition. Both simulation and experimental results are presented. The results show good correlation accuracy in comparison to correlation results obtained for SDF filter synthesized using the original gray-scale images themselves.
[Show abstract][Hide abstract] ABSTRACT: The phase reconstruction in a digital in-line holographic microscopy is compared using two numerical reconstruction methods. The first method uses one Fourier transform and second one uses three Fourier transforms. It is shown that the latter method gives improved object phase reconstruction as compared to the former.
No preview · Article · Jan 2010 · Optics and Lasers in Engineering
[Show abstract][Hide abstract] ABSTRACT: Gray-level data pages enhance the storage capacity of holographic data storage systems. A balanced three gray-scale data page in phase mode produces a homogenized Fourier spectrum which is regarded to be necessary for suitable exploitation of the holographic recording medium. A commercially available transmission type twisted nematic liquid crystal display has been characterized for use as a phase spatial light modulator with phase modulation in the range 0–3π/2 at 532 nm wavelength, such that it may be used for holographic data storage with binary as well as three gray-level phase-modulated data pages. Experimental results of the phase and amplitude modulation characteristics of the SLM, Fourier plane homogeneity, and recording of phase-modulated binary, three gray-level data pages and their reconstruction with a real-time holographic interferometric method are presented.
No preview · Article · Nov 2009 · Optics and Lasers in Engineering
[Show abstract][Hide abstract] ABSTRACT: In this paper, we describe image encryption by combining the images with several matrices made with letters/numerals and placed in the input plane of a double random phase encoding (DRPE) system. Addition or multiplication of several such matrices with an input image provides a modified image pattern which is encrypted in a DRPE system utilizing the 4-f geometry. For gray scale images, the results of encryption in case of addition of matrices are found more reliable and secure as compared to the results of multiplication. Simulation results are presented in support of the idea. Reliability of the technique has been established by evaluating the mean square-error (MSE) between the decrypted and the original image.
No preview · Article · Nov 2009 · Optics and Lasers in Engineering
[Show abstract][Hide abstract] ABSTRACT: In the present paper, we describe the encryption and decryption of two-dimensional images. The encryption is done by employing a sandwich phase diffuser made by using two elongated speckle patterns, and placed in the Fourier plane of a double random phase encoding system. After encryption, the two constituent phase diffusers of such a sandwich diffuser are separated. During decryption, if the conjugate of either of the two elongated phase speckle patterns is used, the image cannot be retrieved. Correct decryption is also not possible if a sandwich diffuser with any of the phase speckle patterns is shifted in position with respect to the other. For decryption, the encrypted image is Fourier transformed and multiplied by the conjugate of the sandwich diffuser, and then the product is further Fourier transformed. It is possible to generate the image only if both the elongated phase speckle patterns are matched point-to-point and then the proper conjugate is made. The use of elongated speckle patterns in constituting a sandwich phase diffuser makes the system less complicated as compared to the use of a sandwich diffuser made with normal speckle patterns, enabling an easy alignment of the random phase diffuser at the time of rejoining the constituent diffusers for making the right key. The ease of alignment is due to the reduction of the requirement of 360° scanning at the time of rejoining these diffusers with little reduction in the security of the system. Simulation results are presented in support of the proposed idea. For optical implementation, the decrypted image may be obtained by generating a phase conjugate wave by the phase conjugation technique, and passing through the same sandwich phase diffuser. To evaluate the reliability of the technique, mean square error (MSE) between the decrypted and original image has been calculated.
No preview · Article · Nov 2009 · Optik - International Journal for Light and Electron Optics
[Show abstract][Hide abstract] ABSTRACT: We propose a method for implementation of gray-scale sparse block modulation codes with a single spatial light modulator in phase mode for holographic data storage. Sparse data pages promise higher recording densities with reduced consumption of the dynamic range of the recording material and reduced interpixel cross talk. A balanced sparse-gray-level phase data page gives a homogenized Fourier spectrum that improves the interference efficiency between the signal and the reference beams. Construction rules for sparse three-gray-level phase data pages, readout methods, and interpixel cross talk are discussed extensively. We also explore theoretically the potential storage density improvement while using low-pass filtering and sparse-gray-level phase data pages for holographic storage, and demonstrate the trade-off between code rate, block length, and estimated capacity gain.
[Show abstract][Hide abstract] ABSTRACT: A double random phase encoding based digital phase encryption technique for colored images is proposed in the Fourier domain.
The RGB input image is brought to HSV color space and then converted into phase, prior to the encryption. In the decryption
process the HSV image is and converted back to the RGB format. The random phase codes used during encryption are prepared
by stacking three two-dimensional random phase masks. These random phase codes serve as keys for encryption and decryption.
The proposed technique carries all the advantages of phase encryption and is supposedly three-dimensional in nature. Robustness
of the technique is analyzed against the variations in random phase codes and shuffling of the random phase masks of a given
phase code. Performance of the scheme is also verified against occlusion of Fourier plane random phase code as well as the
encrypted image. Effects of noise attacks and attacks using partial windows of correct random phase codes have also been checked.
Digital simulations are presented to support the idea.