A. K. Yadav

Fully phase image encryption using double random-structured phase masks in gyrator domain

We propose a method for fully phase image encryption based on double random-structured phase mask encoding in the gyrator transform (GT) domain. The security of the system is strengthened by parameters used in the construction of a structured phase mask (SPM) based on a devils vortex Fresnel lens (DVFL). The input image is recovered using the correct parameters of the SPMs, transform orders of the GT, and conjugate of the random phase masks. The use of a DVFL-based SPM enhances security by increasing the key space for encryption, and also overcomes the problem of axis alignment associated with an optical setup. The proposed scheme can also be implemented optically. The computed values of mean squared error between the retrieved and the original image show the efficacy of the proposed scheme. We have also investigated the schemes sensitivity to the encryption parameters, and robustness against occlusion and multiplicative Gaussian noise attacks.

Devil's Vortex Phase Structure as Frequency Plane Mask for Image Encryption Using the Fractional Mellin Transform

A frequency plane phase mask based on Devil’s vortex structure has been used for image encryption using the fractional Mellin transform. The phase key for decryption is obtained by an iterative phase retrieval algorithm. The proposed scheme has been validated for grayscale secret target images, by numerical simulation. The efficacy of the scheme has been evaluated by computing mean-squared-error between the secret target image and the decrypted image. Sensitivity analysis of the decryption process to variations in various encryption parameters has been carried out. The proposed encryption scheme has been seen to exhibit reasonable robustness against occlusion attack.

Optical Image Encryption Using Devil’s Vortex Toroidal Lens in the Fresnel Transform Domain

We have carried out a study of optical image encryption in the Fresnel transform () domain, using a random phase mask (RPM) in the input plane and a phase mask based on devil’s vortex toroidal lens (DVTL) in the frequency plane. The original images are recovered from their corresponding encrypted images by using the correct parameters of the and the parameters of DVTL. The use of a DVTL-based structured mask enhances security by increasing the key space for encryption and also aids in overcoming the problem of axis alignment associated with an optical setup. The proposed encryption scheme is a lensless optical system and its digital implementation has been performed using MATLAB 7.6.0 (R2008a). The scheme has been validated for a grayscale and a binary image. The efficacy of the proposed scheme is verified by computing mean-squared-error (MSE) between the recovered and the original images. We have also investigated the scheme’s sensitivity to the encryption parameters and examined its robustness against occlusion and noise attacks.

Watermarking in gyrator domain using an asymmetric cryptosystem

A watermarking scheme is proposed based on optical asymmetric cryptography using double random phase encoding in the gyrator transform domain. It is based on the phase and amplitude truncation during the encryption process. The scheme is validated through computer simulations showing the schemes sensitivity to decryption keys and orders of the gyrator transform. The occlusion and noise attacks have also been analysed. The proposed scheme is significantly resistant to both these attacks.

Optical image encryption in the fractional Hartley domain, using Arnold transform and singular value decomposition

A new scheme for image encryption is proposed, using fractional Hartley transform followed by Arnold transform and singular value decomposition in the frequency domain. As the plaintext is an amplitude image, the mask used in the spatial domain is a random phase mask (RPM). The proposed scheme has been validated for grayscale images and is sensitive to the encryption parameters such as order of Arnold transform and fractional orders of the Hartley transform. We have also evaluated the scheme’s resistance to the well-known noise and occlusions attacks.

Optical Cryptography and Watermarking Using Some Fractional Canonical Transforms, and Structured Masks

We have carried out a few studies on image encryption and watermarking in various transform domains, for amplitude and phase images. We have used structured phase masks (SPM) based on devil’s vortex Fresnel lens (DVFL) to enhance security by increasing the key-space. The proposed schemes have been validated by computer simulations and their efficacy is evaluated by computing mean-squared-error (MSE) between the original image and the decrypted image. They have been examined for their sensitivity to various encryption parameters, and robustness to noise and occlusion attacks.

Asymmetric cryptosystem using double random-decomposition in fractional Fourier transform domain

Motivated by recent research on asymmetric cryptosystems, a novel asymmetric scheme for image encryption that uses double random-decomposition technique in the fractional Fourier transform domain is proposed. The scheme endures the Special Attack as against conventional asymmetric cryptosystems based on phase-truncated Fourier transform (PTFT), and equal modulus decomposition. In the proposed scheme, an input image is bonded with a random phase mask and then it is subjected to a fractional Fourier transform. The resulting image is decomposed into two components using the random-decomposition technique. One of them will act as the first private key and the other component is subjected to the second fractional Fourier transform followed by another random-decomposition. Again, two new components are obtained, one will act as the second private key and the other is phase-truncated before subjecting it to LU decomposition followed by affine transform to get the encrypted image. The new scheme possesses enlarged key-space consisting of private keys obtained from random-decomposition, orders of fractional Fourier transform, affine transform parameters and permutation matrix of LU decomposition, thereby having a much greater capability to resist brute force attack. A sensitivity analysis has been carried out with respect to the encryption parameters. In addition to its resistance to the Special Attack, the scheme is immune to the basic attacks such as known-plaintext attack, chosen-plaintext attack, ciphertext-only attack, by virtue of its asymmetric nature. The above analysis along with statistical analysis through 3D plots and correlation distribution establish the strength of the proposed cryptosystem.