Nitin Rawat

Compressive sensing based robust multispectral double-image encryption

We demonstrate a multispectral double-image-based cryptosystem that exploits only a tiny number of random white noise samples for proper decryption. Primarily, one of the two downsampled images is converted into the phase function after being shuffled by Arnold transform (AT), while the other image is modulated as an amplitude-based image after AT. Consecutively, a full double-image encryption can be achieved by employing classical double random phase encryption (DRPE) technique in the fractional Fourier transform domain with corresponding fractional orders. In this study, the encrypted complex data is randomly sampled via compressive sensing (CS) framework by which only 25% of the sparse white noise samples are being reserved to realize decryption with zero or small errors. As a consequence, together with correct phase keys, fractional orders and proper inverse AT operators, lpminimization must be utilized to decrypt the original information. Thus, in addition to the perfect image reconstruction, the proposed cryptosystem provides an additional layer of security to the conventional DRPE system. Both the mathematical and numerical simulations were carried out to verify the feasibility as well as the robustness of the proposed system. The simulation results are presented in order to demonstrate the effectiveness of the proposed system. To the best of our knowledge, this is the first report on integrating CS with encrypted complex samples for information security.

Optical image encryption via photon-counting imaging and compressive sensing based ptychography

In this study, we investigate the integration of compressive sensing (CS) and photon-counting imaging (PCI) techniques with a ptychography-based optical image encryption system. Primarily, the plaintext real-valued image is optically encrypted and recorded via a classical ptychography technique. Further, the sparse-based representations of the original encrypted complex data can be produced by combining CS and PCI techniques with the primary encrypted image. Such a combination takes an advantage of reduced encrypted samples (i.e., linearly projected random compressive complex samples and photon-counted complex samples) that can be exploited to realize optical decryption, which inherently serves as a secret key (i.e., independent to encryption phase keys) and makes an intruder attack futile. In addition to this, recording fewer encrypted samples provides a substantial bandwidth reduction in online transmission. We demonstrate that the fewer sparse-based complex samples have adequate information to realize decryption. To the best of our knowledge, this is the first report on integrating CS and PCI with conventional ptychography-based optical image encryption.

Enhancing the numerical aperture of lenses using ZnO nanostructure-based turbid media

Nanosheets, nanoparticles, and microstructures of ZnO were synthesized via a wet chemical method. ZnO films with a thickness of 44?46??m were fabricated by spray coating, and these have been investigated for their potential use in turbid lens applications. A morphology-dependent comparative study of the transmittance of ZnO turbid films was conducted. Furthermore, these ZnO turbid films were used to enhance the numerical aperture (NA) of a Nikon objective lens. The variation in NA with different morphologies was explained using size-dependent scattering by the fabricated films. A maximum NA of around 1.971 of the objective lens with a turbid film of ZnO nanosheets was achieved.

Controlling band gap and refractive index in dopant-free α-Fe2O3 films

Dopant-free hematite (a-Fe2O3) films are formed at a liquid-vapor interface by means of an easy method in order to control the band gap and refractive index of the films. The a-Fe2O3 films after being transferred to a glass substrate are studied for their structural and optical properties. Control over the thickness of the films in the range from 75 to 400 nm and the constituent nanocrystallite size from 3 to 46 nm is achieved by controlling the synthesis parameters. By controlling the film thickness, crystallite size, and crystallinity of dopant-free a-Fe2O3 films, the optical band gap is increased significantly (by ≈ 0.64 eV) from 2.30 to 2.94 eV, along with increase in the refractive index from 1.35 to 2.8. The observed increase in the optical band gap is explained on the basis of change in lattice symmetry (via change in the c/a ratio) of a-Fe2O3 crystallites.

Single-Pixel Based Double Random-Phase Encoding Technique

A new encryption technique based on single-pixel compressive sensing along with a Double Random-Phase encoding (DRPE) is proposed. As compared with the conventional way of image compression where the image information is firstly capture and then compress, the single-pixel compressive sensing collects only a few large coefficients of the data information and throws out the remaining which gives scrambled effect on the image. Further, to enhance the complexity of the image data, the double random phase encoding along with a fractional Fourier transform is implemented to re-encrypt it. The single-pixel based compressive sensing, DRPE and fractional Fourier transform act as a secret keys. At the receiver end, the original image data is reconstructed by applying the inverse of double random phase process and an \(l_{1}\)-minimization approach. The peak-to-peak signal-to-noise ratio and the minimum number of compressive sensing measurements to reconstruct the image are used to analyze the quality of the decryption image. The numerical results demonstrate the system to be highly complex, robust and secure.

Compressive sensing based ptychography image encryption

A compressive sensing (CS) based ptychography combined with an optical image encryption is proposed. The diffraction pattern is recorded through ptychography technique further compressed by non-uniform sampling via CS framework. The system requires much less encrypted data and provides high security. The diffraction pattern as well as the lesser measurements of the encrypted samples serves as a secret key which make the intruder attacks more difficult. Furthermore, CS shows that the linearly projected few random samples have adequate information for decryption with a dramatic volume reduction. Experimental results validate the feasibility and effectiveness of our proposed technique compared with the existing techniques. The retrieved images do not reveal any information with the original information. In addition, the proposed system can be robust even with partial encryption and under brute-force attacks.