Optical encryption using photon-counting polarimetric imaging

Optical phase-truncation-based double-image encryption using equal modulus decomposition and random masks

This work reports an optical double-image crosstalk free encryption scheme that employs equal modulus decomposition and random masks. For the encryption, two plaintexts by a random amplitude mask and a random phase mask have been encrypted into a single ciphertext mask and two private key masks. Owing to the two random masks introduced, the functional relation between the plaintext pair and the ciphertext indirectly cause the paucity of constraints employed for the specific attack. Unlike the traditional phase-truncation-based techniques, this scheme is immune to the information leakage and different types of attacks. Furthermore, the three different diffraction distances and the illuminating wavelength also function as four additional keys to significantly reinforce the security. Simulation results demonstrate the feasibility and validity of the proposal.

Secret sharing scheme based on spread spectrum ghost imaging

(n,n) secret sharing is a procedure for splitting the key into several pieces so that no subset is sufficient to read the encrypted message except the entire one. In this paper, we propose a novel, to the best of our knowledge, secret sharing scheme based on spread spectrum ghost imaging (SSGI). In the scheme, a dealer divides a secret key, which is obtained by a modulo 2 addition over n sequences from a Hadamard matrix, into n pieces to n participants, and then the dealer uses the secret key as a direct sequence code to encrypt an image using the SSGI method. The resultant bucket signal, as the ciphertext, is then shared with n participants, and the modulated speckle patterns in SSGI are also transmitted to nparticipants by private channels for preventing eavesdropping. An independent signal is used as a protective signal to prevent the information leakage in SSGI. In the decryption process, only if all participants are honest and cooperative, the secret key can be obtained; thus, the ciphertext can be decrypted to the correct image using the second-order correlation algorithm. Otherwise, the image information cannot be extracted. The theoretical analysis shows that the probability of finding out others' pieces for successfully reconstructing the image for one dishonest participant is (1/2^N)^n-1, where N is the length of the secret key, and n is the number of participants. The simulation and experimental results demonstrate that the proposed scheme has a stronger data security capacity in optical information encryption.

Bessel Beam: Significance and Applications-A Progressive Review

Diffraction is a phenomenon related to the wave nature of light and arises when a propagating wave comes across an obstacle. Consequently, the wave can be transformed in amplitude or phase and diffraction occurs. Those parts of the wavefront avoiding an obstacle form a diffraction pattern after interfering with each other. In this review paper, we have discussed the topic of non-diffractive beams, explicitly Bessel beams. Such beams provide some resistance to diffraction and hence are hypothetically a phenomenal alternate to Gaussian beams in several circumstances. Several outstanding applications are coined to Bessel beams and have been employed in commercial applications. We have discussed several hot applications based on these magnificent beams such as optical trapping, material processing, free-space long-distance self-healing beams, optical coherence tomography, superresolution, sharp focusing, polarization transformation, increased depth of focus, birefringence detection based on astigmatic transformed BB and encryption in optical communication. According to our knowledge, each topic presented in this review is justifiably explained.

Optical color image encryption based on chaotic fingerprint phase mask in various domains and comparative analysis

Random phase masks serve as secret keys and play a vital role in double random phase encoding architecture. In this paper, we propose a new, to the best of our knowledge, method to generate the random phase masks using the chaotic Henon map and fingerprint. We then extend the generated chaotic fingerprint phase masks to the Fourier transform domain, fractional Fourier transform domain, Fresnel transform domain, and Gyrator transform domain to encrypt color images. In these four color image encryption schemes, the fingerprint and chaotic parameters serve as secret keys directly, and the chaotic fingerprint phase masks are just used as interim variables and functions. If the sender and receiver share the fingerprint, only the chaotic parameters are needed to transmit over the network. Thus, the management and transmission of the secret keys in these four encryption schemes are convenient. In addition, the fingerprint keys which are strongly linked with the sender or receiver can enhance the security of these four encryption schemes greatly. Extensive numerical simulations have been carried out to verify the feasibility, security, and robustness of these four color image encryption schemes.

Cryptographic key distribution over a public network via variance-based watermarking in compressive measurements

Optical communication has an increasing need for security in public transmission scenarios. Here, we present a protocol for cryptographic key distribution over a public network via a photon-counting compressive imaging system with watermarking, which utilizes a watermarking technique to distribute secure keys, and uses reconstructed images for simultaneous identity authentication and tampering identification. The watermark is embedded in the rearranged compressed measurements of the object, and then the signal is transmitted through a public network. At the receiving terminal, legitimate users can easily extract the watermark as the cryptographic key by using initial keys and the variance characteristic of random measurements. Artificial tampering and attacks can be detected by accurately retrieved images. The realization of this protocol is a step forward toward practical applications, and will be beneficial for the broader fields of optical security in many ways.

Information encryption based on the customized data container under the framework of computational ghost imaging

In this paper, a novel information encryption scheme has been proposed based on the customized data container, where the primary information can be recovered completely from the ciphertext encrypted with computational ghost imaging. From two aspects, the proposed scheme solves the serious issues caused by the inherent linearity and mechanism of computational ghost imaging. First, the primary information to be encrypted is transformed into the bits of information, which is used to control the formation of the customized data container. Then, the exclusive-OR (XOR) operation is performed on it with a randomly generated data container, and the XOR encoding result is scrambled based on the random sequence engendered with the logistic map so that the linearity of the cryptosystem is destroyed. Second, instead of using random phase-only masks, a number of phase masks retrieved from 2D patterns derived from the rows of the designed Hadamard matrix are used to record the measured intensities. The redundancy between these phase masks is low, which can reduce the number of the required phase-only masks greatly. Meanwhile, the conditions of the logistic map are considered as the secret keys, which can enhance the security level greatly due to their high sensitivity to tiny variation. The validity and feasibility of the proposed method have been demonstrated with a set of numerical simulations.

Optical image hiding under framework of computational ghost imaging based on an expansion strategy

A novel optical image hiding scheme based on an expansion strategy is presented under the framework of computational ghost imaging. The image to be hidden is concealed into an expanded interim with the same size as the host image. This is implemented by rearranging the measured intensities of the original object after the process of ghost imaging. An initial Hadamard matrix is used to generate additional matrices by shifting it circularly along the column direction, so that enough 2D patterns are engendered to retrieve phase-only profiles for imaging. Next, the frequency coefficients of the host image are modified with that of the expanded interim by controlling a small weighting factor. After an inverse transform, the host image carrying the hidden information can be obtained with high imperceptibility. Security is assured by considering optical parameters, such as wavelength and axial distance, as secret keys due to their high sensitivity to tiny change. Importantly, differing from other computational ghost imaging based schemes, many phase-only profiles are used to collect the measured intensities to enhance the resistance against noise and occlusion attacks. The simulated experiments illustrate the feasibility and effectiveness of the proposed scheme.

Characterization of Spatial Light Modulator Based on the Phase in Fourier Domain of the Hologram and Its Applications in Coherent Imaging

Although digital holography is used widely at present, the information contained in the digital hologram is still underutilized. For example, the phase values of the Fourier spectra of the hologram are seldom used directly. In this paper, we take full advantage of them for characterizing the phase modulation of a spatial light modulator (SLM). Incident plane light beam is divided into two beams, one of which passes the SLM and interferes with the other one. If an image with a single grey scale loads on the SLM, theoretical analysis proves that the phase of the Fourier spectra of the obtained hologram contains the added phase and a constant part relative to the optical distance. By subtracting the phase for the image with the grey scale of 0 from that for the image with other grey scales, the phase modulation can be characterized. Simulative and experimental results validate that the method is effective. The SLM after characterization is successfully used for coherent imaging, which reconfirms that this method is exact in practice. When compared to the traditional method, the new method is much faster and more convenient.

Image authentication using a vector beam with sparse phase information

We propose a novel optical information authentication scheme that uses Stokes polarimetry of vector beams. Phase-only functions of the plaintext are generated using a modified Gerchberg-Saxton algorithm. Partial information of these phase functions is used to tailor the phase of a vector beam. The Stokes parameters recording of the vector beam generates the ciphertext, which contains sparse information of the input image. In contrast to most authentication schemes, the proposed scheme can authenticate two images from a single real ciphertext. Computer simulation results prove the feasibility of the proposed scheme.

Computer-generated hologram using binary phase with an aperture

Computer-generated holograms (CGHs) have attracted more and more attention in some application fields, such as 3D displays, optical security, and beam shaping. In this paper, a strategy is presented for optical information verification based on CGH using binary phase (1 bit) with an aperture. The input is encoded into the cascaded phase-only masks based on CGH via iterative phase retrieval, and one extracted phase mask is binarized in which one part is selected according to an aperture and further embedded into a random binary-phase host mask. It is numerically illustrated that the reconstructed image can be effectively verified when system parameters, such as aperture and phase-only masks, are correctly applied. It is demonstrated that the proposed method can provide a promising strategy for CGH-based optical verification.

Optical cryptosystem based on single-pixel encoding using the modified Gerchberg-Saxton algorithm with a cascaded structure

In this paper, an optical cryptosystem is developed based on single-pixel encoding using the modified Gerchberg-Saxton algorithm with a cascaded structure. A series of random intensity-only patterns are pre-generated as principal security keys, and phase-only masks for optical encoding and decoding are generated by the modified Gerchberg-Saxton algorithm with a cascaded structure. Subsequently, a series of 1D intensity points, i.e., ciphertexts, are recorded by a single-pixel detector, which may provide a potential for establishing low-cost and compact security systems. The phase-mask generation process can be flexibly designed by modifying the Gerchberg-Saxton algorithm with a cascaded structure; hence high sensitivity and the large indirect space for phase can be guaranteed. It is also illustrated that compared with previous works, the higher eavesdropping percentage is requested to the attackers in the proposed single-pixel optical cryptosystem. The proposed method using a cascaded structure provides a novel strategy for single-pixel intensity-modulated optical security.

Optical encryption in the longitudinal domain of focused fields

We develop a method for encoding information in the longitudinal component of a focused field. Focused beams display a non-zero contribution of the electric field in the direction of propagation. However, the associated irradiance is very weak and difficult to isolate from the transverse part of the beam. For these reasons, the longitudinal component of a focused field could be a good choice for encoding and securing information. Using the Richards and Wolf formalism we show how to encrypt information in the longitudinal domain of the focal area. In addition, we use quantum imaging techniques to enhance the security and to prevent unauthorized access to the information. To the best of our knowledge, this is the first report on using the longitudinal component of the focused fields in optical security.

Optical multiple-image encryption based on the chaotic structured phase masks under the illumination of a vortex beam in the gyrator domain

A novel multiple-image encryption scheme using the nonlinear iterative phase retrieval algorithm in the gyrator transform domain under the illumination of an optical vortex beam is proposed. In order to increase the randomness, the chaotic structured phase mask based on the logistic map, Fresnel zone plate and radial Hilbert mask is proposed. With the help of two chaotic phase masks, each plain image is encoded into two phase-only masks that are considered as the private keys by using the iterative phase retrieval process in the gyrator domain. Then, the second keys of all plain images are modulated into the ciphertext, which has the stationary white noise distribution. Due to the use of the chaotic structured phase masks, the problem of axis alignment in the optical setup can easily be solved. Two private keys are directly relative to the plain images, which makes that the scheme has high resistance against various potential attacks. Moreover, the use of the vortex beam that can integrates more system parameters as the additional keys into one phase mask can improve the security level of the cryptosystem, which makes the key space enlarged widely. Simulation results are given to verify the feasibility and robustness of the proposed encryption scheme.

Creating order with the help of randomness: generating transversely random, longitudinally invariant vector optical fields

We show that it is possible to generate transversely random, diffraction-free/longitudinally invariant vector optical fields. The randomness in transverse polarization distribution complements a previously studied one in intensity of scalar Bessel-type beams, adding another degree of freedom to control these beams. Moreover, we show that the relative transversely random phase distribution is also conserved along the optical axis. Thus, intensity, phase, and polarization of Bessel-type beams can be transversely random/arbitrary while invariant upon propagation. Such fields may find applications in encryption/secure communications, optical trapping, etc.