Isha Mehra

Image fusion using wavelet transform and its application to asymmetric cryptosystem and hiding

Image fusion is a popular method which provides better quality fused image for interpreting the image data. In this paper, color image fusion using wavelet transform is applied for securing data through asymmetric encryption scheme and image hiding. The components of a color image corresponding to different wavelengths (red, green, and blue) are fused together using discrete wavelet transform for obtaining a better quality retrieved color image. The fused color components are encrypted using amplitude- and phase-truncation approach in Fresnel transform domain. Also, the individual color components are transformed into different cover images in order to result disguising information of input image to an attacker. Asymmetric keys, Fresnel propagation parameters, weighing factor, and three cover images provide enlarged key space and hence enhanced security. Computer simulation results support the idea of the proposed fused color image encryption scheme.

Collision in Fresnel domain asymmetric cryptosystem using phase truncation and authentication verification

Abstract. Collision is a phenomenon in which two distinct inputs produce an identical output, so if an attacker finds the encryption keys in such a way that when it is applied to an encrypted image, it produces an arbitrary image instead of original one. We propose collision in an asymmetric cryptosystem based on a phase-truncated Fresnel transform. For encryption, instead of using conventional random-phase masks, structured phase masks with desired construction parameters are used. The decryption keys are generated using the amplitude and phase truncation. An attacker generates an arbitrary (collision) image from the encrypted image using a modified Gerchberg-Saxton phase retrieval algorithm. Two different users, authorized and unauthorized user (attacker), can claim the retrieved image as the original data. The authorized user uses the correct decryption keys and retrieves the original image, while an unauthorized user uses the generated keys and retrieves the collision image. In order to verify the authenticity of the retrieved data, a joint transform correlator is used. A sharp auto-correlation peak is obtained when an image retrieved by authorized user is matched with the encrypted image. However, cross-correlation is obtained when an encrypted image is matched with the collision image. Results of computer simulation support the idea of the proposed collision.

Encrypting digital hologram of three-dimensional object using diffractive imaging

In this paper, we demonstrate three-dimensional (3D) object encryption using diffractive imaging and digital holography. For this purpose, a microlens array has been fabricated using the thermal reflow method, and then its digital hologram is recorded. The hologram of the microlens is encoded based on multiple intensity samplings of the complex-amplitude wave front with axial translation of the image sensor in the fractional Fourier transform domain. Then, the function is Fresnel propagated for three different positions of the camera, and the corresponding diffraction patterns are recorded as cipher-texts. For decryption, an iterative phase retrieval algorithm is applied to extract the hologram from corresponding encrypted images. The corresponding phase profile of the microlens array is then obtained. The simulation results demonstrate that the hologram is decrypted without any stagnation problem and with a rapid convergence rate. High security of the hologram has been achieved in the proposed digital holography-based diffractive imaging scheme. The correlation coefficient, a performance measurement parameter, has been calculated to check the effectiveness of the scheme. The proposed work has been validated through both experimental and simulation results.

Optical image encryption using equal modulus decomposition and multiple diffractive imaging

The equal modulus decomposition (EMD) is a novel asymmetric cryptosystem based on coherent superposition which was proposed to resist the specific attack. In a subsequent work, the scheme was shown to be vulnerable to specific attack. In this paper, we counter the vulnerability through an encoding technique which uses multiple diffraction intensity pattern recordings as the input to the EMD setup in the gyrator domain. This allows suppression of the random phase mask in the EMD path. As a result, the proposed scheme achieves resistance to specific attack. The simulation results and the security analysis demonstrate that EMD based on multiple intensity pattern recording is an effective optical asymmetric cryptosystem suitable for securing data and images.

Gyrator wavelet transform

The gyrator transform is a linear canonical transform, which generates the rotation of an optical signal in position-spatial frequency planes. Gyrator wavelet transform is a relatively newer optical information processing tool obtained by combining the gyrator transform with the wavelet transform. This combination provides multi-resolution analysis of an image which is twisted in spatial frequency planes. The proposed tool satisfies basic algebraic properties, such as the linearity property and Parsevals theorem. Considering the usefulness of this tool, here a study of features, applications, and implementation of the gyrator wavelet transform is presented. This work studies the features of the gyrator wavelet transform, which can find a role in different applications such as edge enhancement, image encryption, image hiding, and watermarking.

Pan-Sharpened Image Optical Encryption

Satellites often capture multispectral and panchromatic images. The fusion of these two images results into a high resolution pan-sharpened image. In this paper, we apply image encryption scheme on the pan-sharpened four color band image. We fuse the multispectral data with panchromatic data in order to form the high resolution pan-sharpened image. Then this pan-sharpened image is separated into four spectral bands. These bands are encrypted using amplitude-, and phase-truncation approach with different fractional Fourier transform orders.

Double image encryption using gyrator wavelet transform

In this paper, we implement a novel optical information processing tool termed as gyrator wavelet transform for the application of double image encryption using amplitude- and phase-truncation approach. This approach enhances the key space in an asymmetric cryptosystem by adding supplementary security layers, i.e., family of mother wavelet and the gyrator transform order. Double input images bonded with random phase masks are independently gyrator transformed. Amplitude truncation of obtained spectrum generates individual and universal keys while phase truncation generates two real-valued functions. Each of the retrieved amplitude function is discrete wavelet transformed, which results into four different frequency bands. We have fused the obtained wavelet spectrum of an individual image by again gyrator transforming them following amplitude- and phase truncation. The obtained real-valued functions corresponding to each image are bonded to form the encrypted image. After using the correct universal key, individual asymmetric key, type of wavelet, and correct gyrator transform order, the original images are retrieved successfully. Numerical simulation results prove that the proposed scheme is more flexible and effective than existing wavelet fusion schemes.

Plasmonics-based Keys for Optical Image Encryption

We have generated the encryption keys from a nanosphere using gyrator transform. Through these keys, an input image has been encrypted using double random amplitude encoding scheme. As a proof-of-concept the simulation results have been presented.

Optical Asymmetric Cryptosystem based on Axial Translation of Image Sensor

An optical asymmetric cryptosystem based on axial translation of charge coupled device (CCD) camera is presented. For decryption, an iterative phase retrieval algorithm is applied with a rapid convergence rate eliminating the stagnation issues.

Vulnerability of asymmetric cryptosystem based on spherical wave illumination against specific attack

In this paper, we claim that asymmetric cryptosystem using spherical wave illumination is vulnerable against specific attack. The combination of spherical wave parameters can easily be obtained in order to decrypt the image through specific attack. We also suggested an improvement so that asymmetric cryptosystem based on spherical wave illumination resists such attacks.