並列摘要
In this thesis, the chaotic image encryption is studied by using properties of chaos including deterministic dynamics, unpredictable behavior and non-linear transform. By these chaotic properties, the positions and values of the pixels of original image are randomly rearranged with the user key. As a result, the cipher image is able to reach a good properties of diffusion and confusion. Our proposed new scheme of chaotic image encryption can be briefly described as follows. At first, we utilize the one-dimensional logistic map to generate the encryption key, scrambling image table and noise image. Then, the source image (i.e., plaintext) is scrambled with scrambling image table and performed exclusive OR operation with the encryption key. Furthermore, several transformed images according above procedures are embedded into a noise image by watermarking techniques to form a pre-encryption image. Finally, scrambling processes and exclusive OR operations with key length of 256, 512 and 1024 bits are executed to obtain the encryption image. Our contribution of the proposed new chaotic image encryption scheme is that, by MATLAB simulation, the cipher images have 6 good characteristics as follows. (1)The correlation between source image and cipher image is very small, almost equal to zero. That is, the source image and cipher image are mostly independent. In addition, the correlation among the cipher images is almost zero. This represents the cipher images are mostly independent, too. (2)The histogram of cipher image pixels is uniform nearly. Namely, our cipher image holds a good confusion property on the statistics. (3)From the simulation of the two-dimensional discrete Fourier transform and shift zero-frequency component of discrete Fourier transform to center of spectrum, we can discovery the energy at the spectrum is consistent, i.e., our cipher image possesses good diffusion property on the statistics. (4)The size of the noise image is able to be adjusted (the size of noise image must equal to or bigger than the size of source image) to protect the source image (plain image). Via the noise image, it lets us to get excellent confusion and diffusion properties of cipher images according to the MATLAB simulations. That is to say, our encryption method derives a good security on communication. (5)Our encryption algorithm is easy to implement on the IC chip. (6)The encryption performance is nice. To sum up, for our proposed new scheme of the chaotic image encryption, the noise image plays a important role. The cipher image characteristic of statistics on confusion and diffusion become excellent due to join the noise image. That is, our new chaotic image encryption method can acquire very fine ciphertext and communication safety.