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In this paper, the security strength of a phase-only asymmetric cryptosystem based on interference and phase-truncated Fourier transforms (PTFTs) has been evaluated. Compared to the conventional PTFTs-based scheme where the plaintext is directly encoded into two phase masks (PMs) and the ciphertext, here the plaintext is firstly converted to the phase-only distribution by PTFTs-based encryption process I, and then modulated by the encryption process II with the aid of two masks generated by a carrier image. The security strength of this cryptosystem has been enhanced by an additional secure layer for the output of PTFTs-based structure. Moreover, the four masks generated in the encryption processes I and II are required for the decryption also, it enlarges the key space which further ensures the security strength of the improved cryptosystem. However, we noticed that the carrier image used to generate one of private keys is same as the ciphertext when the input of the encryption is the zero matrix. Thus, the amplitude mask (AM) as the private key could be recovered by the designed chosen-plaintext attack, and then it can be used as the known parameter in the iterative attacks. Employing the recovered mask, two specific attacks with different constraints are designed to break the cryptosystem based on interference and PTFTs successfully. Based on our cryptoanalysis, it is found that most information of the plaintexts were encoded into the AM and the PM in the encryption process I, and silhouette problem would be caused when one of these keys is known. Numerical simulations have been carried out to validate the feasibility and effectiveness of proposed hybrid attacks. [ABSTRACT FROM AUTHOR]

A novel asymmetric cryptosystem for optical image is proposed using fingerprint based on iterative fractional Fourier transform. To enhance the security, a hyperchaotic phase generated by a 4D Lorenz system is considered as the public key in the proposed encryption system, while the private key is emerged by the retrieved phase and fingerprint. In the encryption process, the secret information is hid into the hyperchaotic phase. Subsequently, the private key can be obtained by a reversible operation. To decrypt the original image, the ciphertext and private key are imported into the input plane of fractional Fourier system. This system is also applicable for information authentication because the fingerprint is used both in encryption and decryption approach. Some numerical simulations have been done to test the validity and capability of the encryption system. [ABSTRACT FROM AUTHOR]

We present an analysis of the noise properties in a ghost telescope and a ghost Fourier telescope imaging systems with shaped incoherent light. By using the analytical result of the point spread function and the numerical simulations, the effects from the shaped incoherent light on the noise and resolution are discussed. Furthermore, we also analyze the effect from the position change of the reference detector. Compared with the widely used Gaussian light source, we find that for both ghost imaging and Fourier-transform ghost diffraction, a cosine-Gaussian source can lead to degradation of the noise and the resolution. However, the noise is increased with a improving resolution when the Gaussian source is modulated by hyperbolic cosine functions. Our results show that one can obtain a good imaging resolution with a relatively small noise by choosing a suitable position of the reference detector. [ABSTRACT FROM AUTHOR]

An analytical expression of a Generalized Bessel–Laguerre–Gaussian (GBLG) beam passing through a paraxial ABCD optical system is developed by using the generalized Huygens–Fresnel diffraction integral. This result is regarded as the main finding of this paper. Several studies such as the propagation of fundamental Gaussian, flat-topped Gaussian, Bessel–Gaussian, Generalized Bessel–Gaussian and Laguerre–Gaussian beams, through an ABCD optical system, are derived as particular cases of our principle investigation. Numerical simulations are performed, in this work, to illustrate the propagation properties of GBLG beam through a free space, a thin lens, a Fractional Fourier transform system and a quadratic graded-index system. [ABSTRACT FROM AUTHOR]

In this paper, a hybrid iris biometric protection scheme using 4D hyperchaotic system by means of coherent superposition and modified equal modulus decomposition in hybrid multi-resolution wavelet domain is proposed. The 4D hyperchaotic framework is employed for producing the permutation keystream for pixel swap-over mechanism. The hybrid multi-resolution is produced by means of Kronecker product of Walsh transform and fractional Fourier transform of different orders. Fractional orders of the hybrid multiresolution wavelet along with the parameters and initial conditions of the 4D hyperchaotic framework, later fill in as additional keys, thus enhancing the key space of the proposed mechanism. The proposed scheme has nonlinear characteristics and has high robustness against brute-force attack attributable to its enormous key-space. Numerical simulations have been carried out on grayscale images to prove the authenticity and efficacy of the proposed cryptosystem. The functioning of the proposed cryptosystem is investigated against various attacks including special attack. Outcomes display that the proposed iris template protection scheme not only has higher robustness against noise attack but is also unassailable to the iterative transform-based attacks. [ABSTRACT FROM AUTHOR]

In this paper, we study an appropriate mathematical model of dark-hollow beam by concerning double-half inverse Gaussian hollow (DHIGH) beams passing through fractional Fourier transform (FRFT) optical systems. Based on Collins integral formula and using the expression of the hard-edged aperture function into a finite sum of complex Gaussian functions, analytical expressions for the propagation properties of DHIGH beams through the FRFT optical systems without and with apertures have been derived in detail. Some numerical simulations are given to illustrate the normalized intensity distribution of DHIGH beams in a FRFT system by studying the important factors of both incident beams order and the FRFT order. Our results obtained by using an approximate analytical formula, are in a good agreement with those obtained by using numerical integral method. The results show that the FRFT optical system is a convenient way for DHIGH beams shaping. [ABSTRACT FROM AUTHOR]