The Scientific World Journal

Volume 2015 (2015), Article ID 123080, 10 pages

http://dx.doi.org/10.1155/2015/123080

## An Experimental Realization of a Chaos-Based Secure Communication Using Arduino Microcontrollers

^{1}Universidade Tecnológica Federal do Paraná, Avenida Alberto Carazzai 1640, 86300-000 Cornélio Procópio, PR, Brazil^{2}Control, Dynamics and Applications Group (CoDAlab), Departament de Matemàtica Aplicada III, Universitat Politécnica de Catalunya, d’Urgell 187, E08036 Barcelona, Spain

Received 7 May 2015; Revised 27 July 2015; Accepted 9 August 2015

Academic Editor: Chengqing Li

Copyright © 2015 Mauricio Zapateiro De la Hoz et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### Abstract

Security and secrecy are some of the important concerns in the communications world. In the last years, several encryption techniques have been proposed in order to improve the secrecy of the information transmitted. Chaos-based encryption techniques are being widely studied as part of the problem because of the highly unpredictable and random-look nature of the chaotic signals. In this paper we propose a digital-based communication system that uses the logistic map which is a mathematically simple model that is chaotic under certain conditions. The input message signal is modulated using a simple Delta modulator and encrypted using a logistic map. The key signal is also encrypted using the same logistic map with different initial conditions. In the receiver side, the binary-coded message is decrypted using the encrypted key signal that is sent through one of the communication channels. The proposed scheme is experimentally tested using Arduino shields which are simple yet powerful development kits that allows for the implementation of the communication system for testing purposes.

#### 1. Introduction

Security and secrecy in communications are some of the most important concerns in societies nowadays. With the advent of worldwide networks and digital communication techniques, the cryptographic techniques that once were restricted to military and state affairs are now covering several domains such as banks, private companies, medical organizations, and so forth. This has led to a very active research field oriented to finding optimal solutions to the problem of communications security [1–3]. As a result, numerous cryptographic techniques that seek to preserve the privacy of the information transmitted have been designed. Chaos is the base of many encryption and decryption techniques because chaotic signals have a highly unpredictable and random-look nature [4].

There are basically two main approaches to designing secure communication systems based on chaotic dynamics: analog and digital. Analog communication systems based on chaos are possible because of the possibility of synchronization [5]. Synchronization occurs when the output of the driving system (master) controls the response system (slave) in such a way that they both oscillate in a synchronized manner. On the other hand, digital chaos communication systems do not depend on chaos synchronization at all. Instead, they usually use one or more chaotic maps in which the initial conditions and the control parameters play the role of the secret key [6].

Several examples of chaos-based communication systems can be found in the literature. For instance, Zapateiro et al. [7] designed a chaotic communication system in which a binary signal is encrypted in the frequency of the sinusoidal term of a chaotic Duffing oscillator. Two chaotic signals of the oscillator are further encrypted with a Delta modulator before they are sent through the channel. In the receiver, a Lyapunov-based observer uses the chaotic signals for retrieving the sinusoidal term that contains the message. A novel frequency estimator is then used to obtain the binary signal. Furthermore, in a new proposal, Zapateiro De la Hoz et al. [8] investigated a modified Chua chaotic oscillator in which the nonlinear term of the original oscillator was changed for a smooth and bounded function that allows for easier analysis and synchronization with other oscillators. An application to secure communications using the modified oscillator was developed and its performance evaluated by numerical simulations. Hammami [9] proposed an image cryptosystem that makes use of hyperchaotic systems. Synchronization was achieved by assuming some structural assumptions of the master system and using some aggregation techniques associated with the arrow form matrix. Fallahi and Leung [10] developed a chaotic communication system based on a chaos multiplication modulator that encrypts the signal. The chaotic signal is generated by using the Genesio-Tesi chaotic system. The authors also prove that the system security could not be broken with the existing methods at that time. Liu and Sun [11] propose a new design of chaotic cryptosystems in which they use high dimensional chaotic maps along with some cryptography techniques to achieve a high security level. The high dimensionality of the map leads to a high complexity and effective byte confusion and diffusion of the output ciphertext at the time that the small key space problem is overcome. Pareek et al. [12] designed an image encryption scheme in which two logistic maps are used along with an 80-bit key to encrypt/decrypt the images. Eight different types of operation are used to encrypt the pixels of an image; the type of operation is chosen according to the outcome of the logistic maps. This secure communication scheme was criptanalyzed in detail in Li et al. [13]. Lee et al. [14] proposed a chaotic cipher stream, a new scheme for generating pseudorandom numbers based on the composition of chaotic maps. The method consists of using one chaotic map to generate a sequence of pseudorandom bytes and then apply some permutation on them using another chaotic map. Shyamsunder and Kaliyaperumal [15] incorporate the concept of modular arithmetic and chaotic maps for image encryption and decryption. Zhang et al. [16] propose a simple but secure chaotic cipher by improving the familiar permutation-diffusion structure.

Numerous works can be found in the literature that use the logistic map for improving security in communications. The logistic map is a nonlinear discrete map originally used for modeling population growth of different species as well as economic and political phenomena [17–19]. However, under certain conditions it exhibits a chaotic behavior [20]. This characteristic has been exploited in cryptography ever since. For example, Murillo-Escobar et al. [21] presented a symmetric text cipher in which they used a 128-bit secret key, two logistic maps with optimized pseudorandom sequences, plain text characteristics, and one permutation diffusions round. Volos et al. [22] presented a chaotic random bit generator and implemented it in an Arduino board. The microcontroller runs side by side two logistic maps working in different chaotic regimes due to the different initial conditions and system parameters. Statistical tests were carried out to prove security against intruders. Pande and Zambreno [23] presented another experimental realization of a chaotic encryption scheme, this time using a Xilin Virtex 6 FPGA. They implemented a modified logistic map that improves the performance of the logistic map in terms of Lyapunov exponent and uniformity of the bifurcation diagram. Other proposals can be found in Lawrance and Wolff [24]; Chang [25]; and Singh and Sinha [26].

In this paper we present a digital chaos communication system in which the logistic map is used to encrypt the message and key of the transmission. A simple Delta modulator is used along with one of the chaotic maps to encrypt the message. The Delta modulation technique is one of the most simple and robust methods of analog-to-digital (ADC) schemes requiring serial digital communications of analog signals [27]. In this work, the transmitter and receiver are implemented in low cost, small but powerful microcontroller boards: Arduino Uno R3 [28]. The Arduino transmitter receives a message which is analog in nature and encrypts it using a logistic map and the Delta modulator. Then the Arduino receiver decrypts the message and converts it to digital form which corresponds to the Delta-modulated signal. In order to obtain the analog version of the message signal, an analog circuitry performs the demodulation and retrieves the message.

This paper is organized as follows. Section 2 describes the problem to be treated and a scheme of the proposed solution. Section 3 is a brief introduction to the logistic map and its applications to secure communications. Section 4 presents the details of the implementation of the proposed technique. Finally the conclusions are presented in Section 5.

#### 2. Problem Statement

The objective of this paper is to design and implement a communication system to transmit a message between two points. The goal is to use the logistic map to encrypt the information as a security means. The proposed communication system scheme is shown in Figure 1 and it consists of the following blocks:(i)*Arduino Transmitter.* This is the core of the transmitter. The Arduino board will take the message through one of its analog input ports. The Arduino will sample the analog input message, , and convert it to the sampled signal , ; is the sampling time, . This signal is then encrypted by using a logistic map and a simple Delta modulator. Afterwards, a key signal, , is generated in order to decrypt the message in the receiver. This key signal is further encrypted using a second logistic map. As a result, the Arduino transmitter generates three outputs: the first one is the encrypted message, , the second one is the encrypted key signal, , and the third one is an auxiliary key signal, , that is used for decryption purposes.(ii)*Channels.* Three wired channels are used to send the encrypted message and key signals.(iii)*Arduino Receiver.* This is one of the two main blocks in the receiver side. It takes the signals , , and to decrypt the Delta-modulated signal before it is converted into its analog form. The output is a digital signal, , which corresponds to the signal .(iv)*Delta Demodulator.* This is the second block in the receiver. It is a Delta demodulator consisting of an integrator, a filter, and some amplifiers to retrieve the original message. Its output is a signal that approximates the original signal .