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Web-based application for cryptographic protocols visualization
Ryšavá, Pavla ; Dzurenda, Petr (referee) ; Ricci, Sara (advisor)
Práce se zabývá vytvořením interaktivní webové aplikace pro substituční šifry a jejich interaktivní kryptoanalýzu. V práci je implementováno šest šifer a zástupci monoalfabetických šifer jsou Caesarova šifra, Atbaš a substituce s klíčovým slovem. Dále zástupci polyalfabetických šifer jsou Vigenrova šifra, Kryptos a Vernamova šifra. Pro interaktivní analýzu je použita frekvenční analýza, index koincidence a n-gramová statistika jako fitness funkce. Výsledek byl dosažen za pomoci HTML5, CSS a skriptovacího jazyka ReactJS což je JavaScriptová knihovna s možností typové kontroly proměnných.
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Side channels - preparation of lab task
Holemář, Jan ; Malina, Lukáš (referee) ; Martinásek, Zdeněk (advisor)
This thesis deals with side-channel cryptoanalysis. It is focused on power side-channel attack on cryptographic device. The smart card Gemalto .NET is used as the cryptographic device. This smart card performs encryption through algorithm RSA, DES, AES. The power consumption of the smart card was scanned by a Tektronix CT-6 current probe. Data obtained by measuring were processed on the computer with relevant software and provided important information about the encryption key that was used.
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Demonstration of Cryptographic Problems through an Interactive Educational Game
Fišarová, Anežka ; Mezina, Anzhelika (referee) ; Mikulec, Marek (advisor)
The bachelor thesis is focused on the design and implementation of a cryptographic interactive educational game. It focuses on various cryptographic ciphers specifically selected so that people outside the field can be introduced to the subject in a demonstrative and entertaining way. Java and JavaFX were used as the programming language. The thesis consists of four parts, the first two are oriented towards the theoretical part of cryptography and the second two are more focused on the practical application and code development. As motivation for the players, a score for correctly cracked ciphers was used. Furthermore, the work includes a choice of difficulty, which influences which ciphers will be presented to the players. At the end of the thesis, the author reflects on the results and explores ways to further improve the methods presented.
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Side-channel cryptanalysis using deep learning methods
Matuška, Jakub ; Martinásek, Zdeněk (referee) ; Sikora, Pavel (advisor)
Cryptographic systems are getting unbreakable on paper. Therefore attacks on the implementations using side-channels are getting in front of others. Especially when neural networks (NN) got involved in this field. With deep learning, these attacks can recover secret keys even on implementations with countermeasures. Deep learning assisted sidechannel analysis (DL-SCA) dominated this field over the statistical methods. That is why it is important to understand its concepts. This thesis will showcase these methods and introduce some new tools regarding correlation power analysis (CPA) and the training of NNs. An attack on ASCAD dataset will take place and the proposed NN to conduct this attack will be evaluated against other models using proper metrics. Lastly, improvements to SITM (See-In-The-Middle) attack using deep learning are proposed and implemented in the console application.
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Triangulation algorithm for non-linear equation systems
Väter, Ondřej ; Hojsík, Michal (advisor) ; Šaroch, Jan (referee)
The topic of this thesis is a triangulation algorithm and its use in cryptanalysis. First of all we will define a non-linear equation system on which we can apply triangulation algorithm and we will explain what its output is. Then we will demonstrate its application in cryptanalysis, more specificaly during the attack on the Rinjdael cifer. We will illustrate this attack by a search of collision for our hash function, created for this purpose in Davies-Mayer mode using Rijndael cipher This thesis also contains a practical part in which we will demonstrate the search of collision for our hash function mention before.
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Applications of Gröbner bases in cryptography
Fuchs, Aleš ; Šťovíček, Jan (advisor) ; Žemlička, Jan (referee)
Title: Applications of Gröbner bases in cryptography Author: Aleš Fuchs Department: Department of Algebra Supervisor: Mgr. Jan Št'ovíček Ph.D., Department of Algebra Abstract: In the present paper we study admissible orders and techniques of multivariate polynomial division in the setting of polynomial rings over finite fields. The Gröbner bases of some ideal play a key role here, as they allow to solve the ideal membership problem thanks to their properties. We also explore features of so called reduced Gröbner bases, which are unique for a particular ideal and in some way also minimal. Further we will discuss the main facts about Gröbner bases also in the setting of free algebras over finite fields, where the variables are non-commuting. Contrary to the first case, Gröbner bases can be infinite here, even for some finitely generated two- sided ideals. In the last chapter we introduce an asymmetric cryptosystem Polly Cracker, based on the ideal membership problem in both commutative and noncommutative theory. We analyze some known cryptanalytic methods applied to these systems and in several cases also precautions dealing with them. Finally we summarize these precautions and introduce a blueprint of Polly Cracker reliable construction. Keywords: noncommutative Gröbner bases, Polly Cracker, security,...
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Time-memory tradeoff útoky
Seidlová, Monika ; Hojsík, Michal (advisor) ; Holub, Štěpán (referee)
Martin Hellman proposed the first time-memory tradeoff attack on block ciphers. It is a chosen plaintext attack, in which the attacker precomputes a large amount of data for some block cipher and can then use it repeatedly in attacks on that block cipher. An improvement suggested by Ron Rivest speeds up the attack by reducing the number of memory accesses. Another modification of the original attack called rainbow tables speeds up the attack even more and brings other advantages. Time-memory tradeoff attacks can also be applied to stream ciphers as known plaintext attacks. This bachelor thesis describes in detail the original attack, its improvements and a modification to stream ciphers. As an example, we summarize an attack on A5/1, a stream cipher used in mobile phones. We also propose a new time-memory tradeoff attack on block ciphers called r-coloured rainbows. The new attack is a modification of Hellman's attack and shares similarities with the rainbow table attack. We give a comparison of the properties of the three attacks and conclude that, for certain block ciphers, our attack may be the most effective of the three.
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Analysis of voice over IP protocols
Boháček, Milan ; El Bashir, Robert (advisor) ; Hojsík, Michal (referee)
In the presented work we focus on both implementation and protocol of the voice over IP application Skype. We analyse several versions of Skype clients and deduce inner workings of the Skype protocol. We present details about the cryptographic primitives used by the Skype clients and their impact on the security of the communication. We emphasize several places of suspicious leaks of the internal states of random generators and deduce rules for the detection of the Skype traffic on the firewall. In the end, we mention a simple enhancement of the current Skype clients that, in practice, can detect an ongoing eavesdropping.
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Key reconstruction from the inner state of RC4
Sladký, Lukáš ; Boháček, Milan (advisor) ; Drápal, Aleš (referee)
In the present work we analyse the key scheduling algorithm of the RC4 stream cipher. The internal permutation generated by the algorithm is biased towards the secret key which can be utilized in the key recovery attempts. Multiple sources were combined to provide proven formulae for these biases. We have completed missing proofs, experimentally verified resulting probabilities and created examples to illustrate usage of the biases in key recovery attempts. This together with methods for extracting information about the secret key gives analysis of the key scheduling algorithm. We have also selected an efficient key retrieval algorithm and implemented an improved version which results in better success probabilities of the key recovery. We have also provided a tool for extracting the key from a permutation obtained by the key scheduling algorithm. Powered by TCPDF (www.tcpdf.org)
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Crytographic attacks on TLS protocol
Oupický, Jan ; Tůma, Jiří (advisor) ; Boháček, Milan (referee)
The aim of this work is to introduce the reader to the protocol TLS and a few selected attacks against the protocol. In the first part we will define the necessary cryptographic definitions used in the following chapters. In the second part we will briefly talk about the history of procotols TLS and SSL and then we will closely look into how they work. The last part is about the analysis of the chosen cryptographically interesting attacks (Padding oracle on CBC mode, POODLE, BEAST and CRIME) against protocols TLS and SSL. 1
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