Chang-Mok Shin

Multilevel image encryption by binary phase XOR operations

We propose a multilevel image encryption by using binary phase exclusive-OR(XOR) operations and image dividing technique. The multilevel image can be divided to binary images that have same gray levels. We convert each binary image to binary phase image by phase encoding and encrypt these images with binary random phase images by binary phase XOR operation. We make encrypted gray image by combining each binary encrypted images. We implement the decryption process with joint transform correlator (JTC) and verify the proposed method by computer simulation.

Digital watermarking technique using Computer-Generated Hologram and optoelectrical extraction algorithm

We propose a digital watermarking technique using a computer generated hologram. The proposed method uses two random patterns separated from the computer generated hologram (CGH). One of those is embedded into the original image as hidden watermark information and then the reconstructed image can be obtained by an optical decoding algorithm with the other one as a decoding key. We analyze an occlusion of the watermarked image that is the original image containing the hidden pattern. The embedding process is performed digitally and reconstruction optically Computer simulation and an optical experiment are shown in support of the proposed technique.

Optical encryption system based on circular polarization and interferometer

We propose an optical encryption system using circular polarization based on interferometer architecture. The phase-modulated input image, represented as orthogonal linearly polarized states by interferometer, is encrypted into circularly polarized states whose direction of the rotation is random. In the decryption we use the inverse matrix of polarization-modulation key and can recover the original polarization states.

Optical Encryption using a Random Phase Image and Shift Position in Joint Transform Correlation Plane

Most optical security systems use a 4-f correlator, Mach-Zehnder interferometer, or a joint transform correlator(JTC). Of them, the JTC does not require an accurate optical alignment and has a good potential for real-time processing. In this paper, we propose an image encryption system using a position shift property of the JTC in the Fourier domain and a random phase image. Our encryption system uses two keys: one key is a random phase mask and the other key is a position shift factor. By using two keys, the proposed method can increase the security level of the encryption system. An encrypted image is produced by the Fourier transform for the multiplication image, which resulted from adding position shift functions to an original image, with a random phase mask. The random phase mask and position shift value are used as keys in decryption, simultaneously. For the decryption, both the encrypted image and the key image should be correctly located on the JTC. If the incorrect position shift value or the incorrect key image is used in decryption, the original information can not be obtained. To demonstrate the efficiency of the proposed system, computer simulation is performed. By analyzing the simulation results in the case of blocking of the encrypted image and affecting of the phase noise, we confirmed that the proposed method has a good tolerance to data loss. These results show that our system is very useful for the optical certification system.

Hierarchical Image Encryption System Using Orthogonal Method

In recent years, a hierarchical security architecture has been widely studied because it can efficiently protect information by allowing an authorized user access to the level of information. However, the conventional hierarchical decryption methods require several decryption keys for the high level information. In this paper, we propose a hierarchical image encryption using random phase masks and Walsh code having orthogonal characteristics. To decrypt the hierarchical level images by only one decryption key, we combine Walsh code into the hierarchical level system. For encryption process, we first perform a Fourier transform for the multiplication results of the original image and the random phase mask, and then expand the transformed pattern to be the same size and shape of Walsh code. The expanded pattern is finally encrypted by multiplying with the Walsh code image and the binary phase mask. We generate several encryption images as the same encryption process. The reconstruction image is detected on a CCD plane by a despread process and Fourier transform for the multiplication result of encryption image and hierarchical decryption keys which are generated by Walsh code and binary random phase image. Computer simulations demonstrate that the proposed technique can decrypt hierarchical information by using only one level decryption key image and it has a good robustness to the data loss such as random cropping.

Single Path Phase-only Security System using Phase-encoded XOR Operations in Fourier Plane

Phase-only encryption scheme using exclusive-OR rules in Fourier plane and a single path decryption system are presented. A zero-padded original image, multiplied by a random phase image, is Fourier transformed and its real-valued data is encrypted with key data by using XOR rules. A decryption is simply performed based on 2-1 setup with spatial filter by Fourier transform for multiplying phase-only encrypted data by phase-only key data, which are obtained by phase-encoding process, and spatial filtering for zero-order elimination in inverse-Fourier plane. Since the encryption process is peformed in Fourier plane, proposed encryption scheme is more tolerant to loss of key information by scratching or cutting than previous XOR encryption method in space domain. Compare with previous phase-visualization systems, due to the simple architecture without a reference wave, our system is basically robust to mechanical vibrations and fluctuations. Numerical simulations have confirmed the proposed technique as high-level encryption and simple decryption architecture.

Improvement of the efficiency from Computer-Generated Holograms by using TS algorithm and SA algorithm

In this paper, we propose a method for optimizing a computer-generated hologram(CGH) by combining the Tabu Search(TS) algorithm with the Simulated Annealing(SA) algorithm. By replacing an initial random pattern of the SA algorithm with an approximately ideal hologram pattern of the TS algorithm, we design a CGH which has high diffraction efficiency(DE). We compared the performance of the proposed algorithm with the SA algorithm using computer simulation and an optical experiment. As a result, we confirmed diffraction efficiency and uniformity to be enhanced in the proposed algorithm.

Binary phase-based optical encryption system using interferometer

In this paper, we propose a new image encryption and decryption system using a phase-modulated random key and the principle of interference. This optical system makes an encrypted image by the multiplication of a random phase key and a phase-modulated image. The random key and an image consist of only binary values. Thereafter a phase value of every pixel of the encrypted image is 0 or pi. The reconstructed pattern of the original image is simply performed by interfering between reference wave and a direct pixel to pixel mapping image of the encrypted image with the same random phase key. In optical experiment, both computer simulation and optical experiment show a good performance of the proposed optical method as encryption scheme.