Kehar Singh

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.

Double Random Phase Encoding Based Optical Encryption Systems Using Some Linear Canonical Transforms: Weaknesses and Countermeasures

During the last two decades or so, a large number of optical information security systems have been proposed by researchers, by exploiting various inherent advantages of optics, with a view to gaining superiority over the existing digital security systems. Among them, double random phase encoding (DRPE) scheme is the oldest and most exhaustively explored optical scheme. However, symmetric nature and linearity prove to be bane of the DRPE scheme, and give an open invitation to unauthorized users to crack the system by mounting different type of attacks. Due to this fact, security of the DRPE scheme has been compromised, making the system vulnerable to attacks. A number of schemes have also been introduced based on the use of fractional Fourier-, Fresnel-, gyrator-, Hartley-, and other transforms. However, vulnerabilities are not limited only to the Fourier domain based systems. Fresnel- and fractional Fourier domain based systems have also been found weak against the chosen-, and the known-plaintext attacks. Resistance of many of the security enhanced DRPE schemes in some other linear canonical transform domains has also been found to be weak against these attacks or their modified forms. When linearity is claimed to be broken with introduction of an amplitude mask at the Fourier plane, the DPRE scheme is able to nullify the high level known-plaintext attack but susceptibility is found against a simple impulse function attack. Recently, some strategies have been adopted to improve the resistance of the DRPE based schemes against the impulse function attacks. Some aspects of the problem have been discussed in the present chapter.

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 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.