Research Of Digital Image Encryption

With the rapid development and widespread application of image processing technique, image data have become an important form of information representation. Meanwhile, the security of images is a major concern.Cryptography is an effective approach to achieving information security. Due to some appealing features of a chaotic mapping such as pseudo-randomness and sensitivity to the initial values and parameters, design and analysis of encryption systems based on chaotic mappings has now been one hotspot in modern cryptography.This thesis addresses image encryption based on chaotic mapping.First, the principle and state-of-the-art of the chaotic image encryption are reviewed, with emphasis on a previously proposed encryption algorithm, known as the Fridrich's algorithm, that can achieve a high level of security by synthesizing the scrambling and diffusion operations.After careful analysis of the Fridrich's algorithm, we propose an improved scheme by introducing three operations:①Scramble the pels of an image using a two-dimensional logistic mapping. This operation significantly enhances the effect of image scrambling.②Exchange the imported pels. This operation effectively avoids coordinates collision and remarkably improves the encryption efficiency.③Incorporate a chaotic signal in the diffusion operation. This operation acquires excellent diffusion effect. Both simulation results and theoretical analysis justify the utility of the proposed algorithm because it has a large key space, is very sensitive to the secret key as well as the original image, and is resistant to common attacks.