Study Of The Optical Encryption And Verification Techniques

With the development of the information technology, traditional information security techniques (i.e. encryption techniques and verification techniques) are not qualified for processing the enormous amount of data in the future. This is due to the traditional techniques are implemented by electronic approaches, such as computers or DSPs, and therefore limited by their processing speed. As a newly developed technique, optical information security technology is progressing rapidly in recent years. It is an important supplement and promotion to traditional security techniques. Optical information techniques are intrinsically of high speed and parallel processing. They also have large information capacity because the wavelength of light is very short. And in the mean time, they are multi-dimensional information carriers because they have many properties including amplitude, phase, wavelength and polarization. These merits establish the innate advantage of optical approaches compared with traditional electronic approaches in tasks like data encryption and verification.After thorough investigation and analysis, and according to several substantial defects in current optical encryption systems and optical verification systems, we carried out a series of theoretical and experimental researches. Several novel and improved methods were put forward. Most proposed methods were proved by optical experiments with satiable results. Our research mainly includes the following works:(1) According to the problem of key design in the JTC encryption system, the G-S and the Sleek Revise algorithms were analyzed, and their advantages and disadvantages were summarized. In order to take advantages of both algorithms, the Iterative Algorithm based on Fuzzy Control Theory was put forward. Designing results showed that the decryption quality of key designed from the Iterative Algorithm based on Fuzzy Control Theory is better than that of key designed from G-S and Sleek Revise algorithms.(2) The optic-electronic hybrid verification technique based on Fourier encoding was studied experimentally. Experimental study of this technique had never been reported before our work. Optical decoding setups based on single Fourier lens and based on Mach-Zehnder interferometer architecture were put forward, respectively. Optical experiments using the two setups were carried out, proving the correctness of the verification technique. Finally, an improved encoding method using multiple key masks was put forward, and its validity and robustness were proved by experiments. (3) In the optic-electronic hybrid verification technique, the decoded result is always symmetrical. Therefore, the useful information is only a fraction of the whole image. To solve this problem, an optic-electronic hybrid certificate validation technique based on Fresnel encoding was proposed. Experimental result proves the validity and reveals some advantages of the method. The decoded result can be asymmetrical, so that more useful original information can be encoded. The security level is also enhanced by importing the Fresnel diffraction range z as another key. In experiment, contrast of the decoded image is increased by a 4-f spatial filter system.(4) A novel optical security technique for safeguarding user passwords base on optical fractal synthesizer was proposed. The user password is protected by being converted into a fractal image using the Optical Fractal Synthesizer (OFS). Setup of OFS in previous literature is complicated. And their output image is degraded since too many elements are involved. Here we presented a new setup of OFS requiring fewer optical elements. Experimental result proved the validity of the technique. The system is robust to turbulences and element position errors in the OFS.