# Prototyping the Symmetry-Based Chaotic Communication System Using Microcontroller Unit
## 1 Introduction  
The interest in message transmission by chaotic signals greatly increased after the discovery of the phenomenon of chaotic synchronization. [PERSON] et al. proposed an approach called chaotic masking [1]. Authors indicate that chaotic signals are good candidates for masking information in carrier waveforms due to their broadband and noise-like behavior. The disadvantage of chaotic masking is its low secrecy: various attack methods were proposed (short-time zero-crossing rate, STZCR) to recover the transmitted message [2]. Chaotic shift keying (CSK), an alternative approach to chaotic masking, appears to be more secure and robust against noise. In 1996, a kind of CSK called a parameter modulation (PM) was presented [2]. It can be used to transmit both digital and analog signals. Being a method of the family of so-called coherent methods of chaotic communication, implying the presence of chaotic synchronization, both CSK and PM make it possible to reliably conceal the message and the very fact of the transmission. They became common technologies broadly discussed in studies on chaotic communication until today [3; 4; 5]. However, multiple methods were proposed for cracking CSK and PM by simple attacks, such as return map analysis [6] and spectrum analysis [7]. Later, [PERSON] et al. investigated attacks and counteraction techniques more deeply [8; 9]. The general conclusion was that the parameter modulation is not sufficiently reliable against attacks, and some modifications are required to improve it [10]. Recently, a modulation method conceptually close to PM called symmetry coefficient modulation (SCM) [11; 12] was proposed. This modulation method is implementable in digital hardware and is suggested to possess much better security properties [13]. From the security and concealed messaging point of view, this method seems to be promising. Therefore, it is of interest to evaluate this type of modulation experimentally in real digital equipment and a physical communication channel with the presence of noise. Solutions for the physical implementation of chaotic communication include both analog and digital cases. The first proposed solutions in chaos-based communications were analog. Such studies involving new types of attractors, modulations, etc., are still an active field of study [14; 15; 16]. Meanwhile, an increasing number of researchers are focusing on digital electronics. The advantages here are flexibility, native support of digital data, and the ability to implement complex modulation and digital signal processing algorithms. The main disadvantage is the relatively low transmission speed. Therefore, proof of the concept may be achieved using microcontrollers (MCUs), and practical solutions must be implemented on a field-programmable gate array (FPGA) or application-specific integrated circuits (ASIC) with a better performance. Among MCU-based prototypes, implementations of chaotic communication systems (CCSs) based on the Arduino platform have become widespread due to their low cost, easy programming, and the plenty of features convenient for CCS realization, such as floating point numbers arithmetic and built-in ADC/DAC. [PERSON] et al. [17] recently used Arduino Due to show its potential in real-time memristive chaotic system implementation in image encryption tasks. [PERSON] et al. [18] proposed a visible light communication (VLC) system involving LED and optical sensors based on Arduino Due. A software-implemented Rossler chaotic oscillator was used to modulate a digital signal transmitted as an encrypted light stream. [PERSON] et al. [19] used a multi-directional multi-scroll chaotic oscillator and Hamiltonian-based controller to establish a secure communication system on the Arduino Mega board. A monochromatic image of 64 x 64 bits was securely transmitted using this system.