Optical image encryption technique based on deterministic phase masks

Abstract

Abstract. The double random phase encoding (DRPE) scheme, which is based on a 4f optical correlator system, is considered as a reference for the optical encryption field. In this work, we propose a modification of the classical DRPE scheme based on the use of a novel class of structured phase masks, the deterministic phase masks. In particular, we propose to conduct the encryption process by using two deterministic phase masks, which are built from linear combinations of several sub-keys. For the decryption step, the input image is retrieved by using the complex conjugate of the deterministic phase masks, which were set in the encryption process. This new concept of structured masks gives rise to encryption-decryption keys which are smaller and more compact than those required in the classical DRPE. In addition, we show that our method significantly improves the tolerance of the DRPE method to shifts of the decrypting phase mask -when no shift is applied, it provides similar performance to the DRPE scheme in terms of encryption-decryption results-. This enhanced tolerance to the shift, which is proven by providing numerical simulation results for gray-scale and binary images, may relax the rigidity of an encryptiondecryption experimental implementation set-up. To evaluate the effectiveness of the described method, the meansquare-error (MSE) and the peak signal-to-noise ratio (PSNR) between the input images and the recovered images are calculated. Different studies based on simulated data are also provided to highlight the suitability and robustness of the method when applied to image encryption-decryption processes.

Watermarking image encryption using deterministic phase mask and singular value decomposition in fractional Mellin transform domain

“…The DPM of size (256 × 256) divided into 16 subkeys of size (64 × 64). The resulting DPM can be written as a linear combination of the stated 16 sub-masks M i, j as given by the following expression [37,38]:…”

“…Uses of SPM entail increases additional encryption keys, enlarges the key space which avoids problems arising from misalignment and has benefits of a higher space-bandwidth product. Recently, Zamrani et al [37] and Girija and Singh [38] proposed a class of SPM called deterministic phase mask (DPM) which is an order of encryption parameter m and a linear combination of several sub-keys (SKs). The result of their technique demonstrates several interesting features in comparison to the classical DRPE.…”

Optical triple random-phase encryption

“…4(b) and (c)) into the TRPE encryption process given in Eq. (10). By doing this, the Dirac delta function encrypted image e TRPE ( x , y ) | CPA was obtained for the TRPE case, which is pictured in figure 5(d).…”

“…In recent years, research on optical techniques for image encryption has gained a great potential owing to their high parallel processing speed and large storage memories [1][2][3][4][5][6][7][8][9][10]. The main motivation for using optics for information security is that optical waveforms possess many complex degrees of freedom such as amplitude, phase, polarization, large bandwidth, nonlinear transformations, quantum properties of photons, and multiplexing that can be combined in many ways to make information encryption more secure and more difficult to attack.…”

Optical image encryption using gamma distribution phase masks in the gyrator domain

“…For security enhancement, another alternative is to use structured phase key (SPK) in the encryption-decryption process instead of white-noised RPK. Several kinds of SPK have been constructed, such as fractal zone mask [32], linear phase mask [33], toroidal zone mask [34][35][36], spiral phase mask [37][38][39][40][41][42][43][44], etc. All these SPKs have shown significant simplicity and robustness to meet the requirements of high flexibility and safety.…”