Optical Encryption And Digital Watermark In Information Security

With the remarkably rapid development of the computer and Internet, information security has been widespread concerned. Encryption is a noticeable branch of information security. Conventional encryption is achieved by means of the computer; however, these methods are constrained in speed and cost. In recent years, owing to processing with high speed and parallelism, large key space, low cost, there have been a great number of optical encryption methods.First of all, this paper describes the basic theory of information security and digital watermark. We introduce the double random phase encryption development at home and abroad. Meanwhile, we simulate the main methods. Then, a traditional digital hologram watermark based on Fourier Transform is introduced. We draw the following conclusions through detailed analysis of this method:(1) Principle of this method is simple. It can be easy to implement. Also, it is a blind watermark;(2) However, security of this method is poor because doing only a Fourier inverse transform will extract the watermark. Meanwhile, quality of the extracted watermark is contradictory from the distortion rate of the embedded image.As the tradition hologram watermark technique is easy to be picked up, some improvements are made. A digital hologram watermark technique based on Fresnel Transform is presented. These are the improved points:(1) We use Fresnel Transform instead of Fourier Transform;(2) The watermark is embedded in part of the image;(3) We process the embedded image with Gray-scale adaptivity and edge pixel interpolation.And the wavelength, the diffractive distance, the position of the watermark embedded, the size of the watermark are used as keys. The simulation results indicate that this method is safer.Finally, we introduce the use of phase holograms improvement program, which does not change the amplitude of the host. In this method, we achieve the phase change through thickness of the host micro-changes. Therefore, the watermarking is not easy to detect.