Grayscale image chaotic secure communication based on CNN chaotic synchronization principle

The so-called confidential communication is to prevent the secret of communication from being stolen. In the process of communication, confidential information and its transmission method are concealed to achieve the purpose of confidentiality. Chaos is a form of motion unique to nonlinear dynamic systems. Since the principle of chaos synchronization was proposed in 1990 and realized in circuits, chaos control and synchronization and its application have quickly become a hot topic in the field of nonlinear research. At the same time, chaos phenomena have the characteristics of ergodicity, non-periodicity, continuous broadband spectrum, and noise-like properties, which are particularly suitable for confidential communication and image encryption. At present, chaotic confidential communication can be roughly divided into three categories: the first category is to directly use chaos for confidential communication, such as the experiment of using Logistic mapping to encrypt and decrypt voice signals based on single-chip microcomputers [1], and the experiment of using Logistic mapping and Henon mapping to encrypt and decrypt image signals based on PCs [2]; the second category is to use chaos synchronization for confidential communication [3-4]; the third category is asynchronous communication of chaotic digital coding. Among them, the second category of chaotic synchronization confidential communication is a major research hotspot in the world.
Based on the principle of chaotic synchronization of cellular neural network (CNN), this paper conducts a grayscale image secure communication experiment based on a single-chip microcomputer. The feasibility of the scheme is verified by comparing the noise-free, different degrees of noise interference and synchronization performance.
1 CNN Chaotic Model
The four-element CNNs chaotic synchronization secure communication is shown in Figure 1 [4].

Launch system:

Transmission signal:
s(t)=KX+200y4+i(t)

Through the same driving variable s(t), the synchronization error e=xx′ is achieved. When e=0, that is, when the equilibrium state is stable, the constructed receiving equation is as follows:
Receiving system:

In the formula, take K=[80.190 0, 20.154 6, 11.936 3, -89.800 0].
2 System Design
2.1 Single Chip Microcomputer and Development Tools
The single chip microcomputer used in this paper is AT89S52, on which grayscale image chaotic secure communication is realized. AT89S52 is a low-power, high-performance CMOS integrated circuit chip 8-bit microcontroller with 8 KB system programmable Flash memory. It is manufactured using Atmel's high-density non-volatile memory technology and is fully compatible with the industrial 80C51 single chip microcomputer instructions and pins. The on-chip Flash allows the program memory to be programmable in the system. On a single chip, with a smart 8-bit CPU and in-system programmable Flash, the AT89S52 can provide highly flexible and super-effective solutions for many embedded control application systems.
The single chip microcomputer development tool used in this paper is Keil C51, version 808A. This development tool supports assembly/C language programming. And provides a variety of analog chips for software simulation. Keil C51 is a 51 series compatible microcontroller C language software development system produced by Keil Software in the United States. Compared with assembly language, C language has obvious advantages in function, structure, readability, and maintainability, and is easy to learn and use.
2.2 Design process
Grayscale image is a two-dimensional signal, and the signal required for this design is a one-dimensional signal. Therefore, before the experiment, the two-dimensional dot array (m×n) of the grayscale image must be converted into a one-dimensional array as shown in Figure 2 as the input signal i(t).

The whole experimental process is shown in Figure 3. It should be noted that due to the limited storage unit of the single-chip microcomputer, the chaos algorithm generates a large number of intermediate parameters after multiple multiplication and addition. In order to obtain complete data results and the normal operation of the single-chip microcomputer, 5 data are set as one algorithm cycle. Once one algorithm cycle is completed, the result data is sent to the computer, and the next cycle result is overwritten and saved in the same storage unit. In this way, the integrity of the data and the fluency of the experiment are guaranteed.

3 Experimental results
The experimental interface is shown in Figure 4, and the functions are as follows:
Noise parameter: communication noise, simulating the experimental results under external interference in the actual environment.
Synchronization parameter X: 4-element CNN chaos algorithm, X initial value, indicating the synchronization of communication, when X is 0, it means synchronization; when it is greater than zero, it means undersynchronization, the larger the X value, the worse the synchronization performance.

Pass test: Test whether the microcontroller is connected correctly.
Run: If the pass test is normal, click Run, and the display will be as shown in Figure 4.
The results obtained by entering different noise parameters and synchronization parameters are shown in Figure 5.

Based on the CNN chaos synchronization principle, this paper realizes the confidential communication of grayscale images on a single-chip microcomputer. The experimental results are compared under different noise coefficients and synchronization coefficients, as shown in Figure 5. Under ideal conditions (i.e., when the noise is 0 and the synchronization is complete), the feasibility of chaotic confidentiality on a single-chip microcomputer is verified. However, when the noise gradually increases, the image distortion becomes higher and higher, which is in line with the actual situation. When the synchronization parameters change, the image is undersynchronized, which confirms the correctness of the synchronization algorithm on the single-chip microcomputer. As a small chip device, the single-chip microcomputer can be embedded in various electronic products, with a wide range of applications, low cost, high efficiency, and stable confidential communication effect.