BORKOVEC, O. Synchronizace chaotických dynamických systémů [online]. Brno: Vysoké učení technické v Brně. Fakulta strojního inženýrství. 2019.

Posudek vedoucího

Tomášek, Petr

The thesis deals with synchronization of chaotic dynamical systems and its application in cryptography. The student presented a theoretical background and then he discussed an application of chaotic systems and their synchronization process in encryption/decryption of secret message. The student implemented the synchronization procedures and encryption/decryption process in Matlab environment. There are discussed two types of messages – a digital bit stream and a greyscale picture. There was considered a deeper analysis of message encoding, especially some simulations in the case of picture messages. Unfortunately, it was not done for lack of time. There is several factual, grammar and formal errors in the thesis, e.g. p. 17, line 8 – an extra “to” p. 21 Theorem 1.6 – there should be V(x)>0 instead of V(x*)>0; and incorrect formulation of conditions a,b,c - misprints – missing 0 and brackets. In references the papers [10] and [14] are the same. The matlab scripts should be uploaded together with the pdf of the thesis to the system for revision purposes, but they are missing. The resolution of several graphical outputs is too small. Anyway, the student proved his analytical and programming abilities. The overall impression of the thesis is good and the final overall assessment is B/very good.

Posudek oponenta

Opluštil, Zdeněk

The master’s thesis deals with synchronization of chaotic dynamical systems. It is divided into three main parts. The first one includes an introduction to dynamical systems - basic definitions and statements which are used later. Then three known chaotic systems (Lorenz, Rossler, Chua’s circuit) are analyzed. Next part provides basic overview of synchronization methods and their applications to the above mentioned systems. Finally, author discusses the use of these methods in signal coding. Obtained theoretical results were verified by algorithm created in mathematical software MATLAB (algorithm codes are added in the appendix). The author fulfilled the requirements and goals of the master’s thesis. The text is clear and logically structured. It contains some typos e.g. p. 21, line 8: x^* in R p. 21, line 33: V(x)>0 p. 21, line 34: V(x)0 p. 21, line 33: V(x) 0 p. 34, line 15: (3.5) p.36, line 10,11: [?] p.52: papers [10] and [14] are the same etc. The main focus of the thesis is in chapter three and four, where author presents two methods of synchronization of chaotic systems (complete synchronization and negative feedback synchronization - he used results established in [12], [13], [14]) and applies them into signal coding. More precisely, encryption and decryption of digital binary valued bit-stream and analogue waveform signal is demonstrated in chapter four. In this master’s thesis, I especially appreciate the effort to apply theoretical results in practise. For example secret message transmission and recovery is an interesting application. But the question is whether this is applicable in practice. The author also did a lot of work in programming codes and algorithms in mathematical software MATLAB to illustrate numerical solutions of considered problems. Unfortunately, presented graphs and pictures are too small and of poor quality so the reader has a problem with recognizing the solutions. I recommend the thesis for the defence with classification C.

eVSKP id 116908