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Applied Optics

Color information cryptosystem based on optical superposition principle and phase-truncated gyrator transform

Muhammad Rafiq Abuturab

Published Nov 20, 2012• 52 citations
Publisher

Abstract

A novel asymmetric color information cryptosystem based on an optical coherent superposition method and phase-truncated gyrator transform (GT) is proposed. In this proposal, an original color image is converted into three independent channels, i.e., red, green, and blue. Each channel is separated into a random phase masks (RPM) and a key phase mask (KPM) using a coherent superposition method. The KPM is a modulation of the RPM by the color channel and used as decryption key. The same RPM, which is independent of plaintext, can be chosen for different images of the same size; however, KPMs, which are related to the original color images, are different. The RPM and the KPM are independently gyrator transformed. Then two gyrator spectra are, respectively, phase truncated to obtain two encoded images and amplitude truncated to generate two asymmetric phase keys. The KPM and two phase keys provide asymmetric keys. The transformation angles of the GT give additional keys for each channel and thus offer a high-level robustness against existing attacks. The proposed optical design is free from axial movement. Numerical simulations are demonstrated to verify the flexibility and effectiveness of the proposed method.

DOI
10.1364/ao.51.007994

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Abstract We develop a novel method to encrypt a color image by combining enhanced optical interference with phase retrieval algorithm and linear phase color-blend (LPCB). In this method, the original color image is encoded into three phase only masks (POMs) with different Fresnel diffraction distances and one fixed random phase mask (RPM). For the decryption in an optical interference system, the three individual POMs are placed in the red, green and blue channels, respectively, and the RPM is placed in the public channel. Only if the right POMs and RPM are fixed in their positions properly, one could achieve the expected information. Compared with traditional interference based color image method, our method eliminates the silhouette problem fully. LPCB is also introduced to modulate the phase value of each pixel of the three POMs to further enhance the security. Numerical simulation results are presented to illustrate the feasibility and effectiveness of the proposed scheme.
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We propose an improved method of attack on an asymmetric cryptosystem based on a phase-truncated Fourier transform. With the proposed method of attack, an attacker is able to access the exact decryption keys and obtain precise attack results. The method is based on a novel median-filtering phase-retrieval algorithm. Compared with existing attacks, the proposed attack has the following advantages: (1) exact information of the original image can be obtained in gray-scale and binary forms; (2) better computing efficiency; (3) more robust against noise and occlusion contaminations. Numerical simulation results show the effectiveness and robustness of the proposed method. Based on the proposed method of attack, we further propose a new cryptosystem, which not only enhances the security of the system but also does not require truncated phases.