以经典的Lorenz 系统为研究对象,利用FPGA 数字信号处理技术实现 Lorenz 混沌系统,减少了外界因素的干扰. 首先,对Lorenz连续系统的方程进行分解,得到离散化状态方程,接着基于DSP-Builder软件开发平台获得系统的电路模型,该模型可直接转化为VHDL语言;其次,采用硬件描述语言( Verilog HDL)直接编程的形式,对系统进行验证,并从示波器中观测到Lorenz系统的混沌波形. 通过比较上述2种实现混沌系统的方法,总结其优缺点及适用范围,为进一步利用FPGA实现一类非线性系统及

With the increasing requirements of the performance in secure communication filed based on chaos, chaotic systems have been gradually developed into higher dimensions. Because the sequence generated by onedimension chaos, such as Chebyshev map has the problem of weak chaotic properties and uneven distribution, a new two-dimensional chaotic map, called Logistic-Adjusted-Chebyshev map (2D-LACM), is proposed in this paper which enlarges the range of chaotic control parameter, and expands the range of surjection to the entire control parameter interval to make the distribution of the sequence more uniform. Compared with other improved chaotic maps, the proposed 2D-LACM in this paper has more complex chaotic properties and better ergodicity. Next, a visualized image encryption algorithm based on 2D-LACM is proposed (LACM-VIEA), which can encrypt the plain image into a noisy image, and then embed it into a cover image of the same size. In order to demonstrate the security of LACM-VIEA, the algorithm is analyzed in detail from the aspects of key, histogram, visual effect, robustness and anti-plaintext attacks, etc. The final analysis results show that LACM-VIEA has good security performance.

A new two-dimensional chaotic system in the form of a cascade structure is designed, which is derived from the Chebyshev system and the infinite collapse system. Performance analysis including trajectory, Lyapunov exponent and approximate entropy indicate that it has a larger chaotic range, better ergodicity and more complex chaotic behaviour than those of advanced two-dimensional chaotic system recently proposed. Moreover, to protect the security of the crowd image data, the newly designed two-dimensional chaotic system is utilized to propose a visually meaningful image cryptosystem combined with singular value decomposition and Bernstein polynomial. First, the plain image is compressed by singular value decomposition, and then encrypted to the noise-like cipher image by scrambling and diffusion algorithm. Later, the steganographic image is obtained by randomly embedding the cipher image into a carrier image in spatial domain through the Bernstein polynomial based embedding method, thereby realizing the double security of image information and image appearance. Besides, the visual quality of the steganographic image can be improved by the adjustment factor according to different carrier images during the embedding process. Ultimately, security analyses indicate that it has higher encryption efficiency (2 Mbps) and the visual quality of steganography image can reach 39 dB.