National Repository of Grey Literature 10 records found  Search took 0.01 seconds. 
Solving AX-equations
Butora, Jan ; Tůma, Jiří (advisor) ; Joščák, Daniel (referee)
Title: Solving AX-equations Author: Jan Butora Department: Department of algebra Supervisor: doc. RNDr. Jiří Tůma, DrSc., Department of algebra Abstract: In this work, we present concept of AX-equations and focus on two such equations. Using similiar techniques, we build a theory for both equations, which allows us to express number of their solutions based only on their parameters. Using this theory, we demonstrate on an example that differential steps, used in differential cryptanalysis of modular addition, are not independent. Moreover, based on this theory we introduce and implement fast algorithms for searching solutions. Keywords: differential cryptanalysis, AX-equations, modular addition, carry, sol- vability condition
Algebraic and combinatorial methods for the study of hash functions
Joščák, Daniel ; Tůma, Jiří (advisor) ; El Bashir, Robert (referee) ; Rosa, Tomáš (referee)
The work summarizes author's research during the doctoral studies in the field of hash functions. The first part of the thesis presents a generalised theory of equations built from two basic building blocks of cryptographic primitives: modular addition and eXclusive OR. In particular we study AX-equations of depth 1. The second and third sections were written after Wang's publication of collisions in MD5 and show that minor modifications of the hash function does not work. We present collisions in the 3C and 3C+ constructions of hash function suggested by Gauravaram and feedback ring-iterative structure by Su et al. The results were published at the conferences ICISC 2006 and SPI 2007. The last part presents a newly constructed type of collisions in MD5 with a newly proposed message differences. The result was published and presented at the conference Indocrypt 2008. Powered by TCPDF (www.tcpdf.org)
Concrete Security of the IPSec Protocol
Švarcová, Marie ; Rudolf, Bohuslav (advisor) ; Joščák, Daniel (referee)
The main goal of this thesis is to articulate and to prove security properties of the key exchange protocol IKE, through which the IPSec protocol establishes agreement on keys used for securing internet traffic. It also covers the description of differences between asymptotic and concrete security treatments and the notions of key exchange security and the security of underlying primitives used by key exchange protocols, in the context of concrete security. A general description of IPSec and its main functionalities follows, accompanied by detailed descriptions of both versions of IKE (IKEv1, IKEv2). A general introduction to key exchange is also included and a representative of signature-based version of IKE is introduced and its security is analysed. Powered by TCPDF (www.tcpdf.org)
Anylysis of cryptographic functions in the PDF format
Štíchová, Kateřina ; Růžička, Pavel (advisor) ; Joščák, Daniel (referee)
The present work is focused to cryptographic functions in PDF format. The aim is to examine problems with long-term archiving of documents in PDF format. It cryptographic functions used in the documents are for long-term archi- ving problem. There is a lot of ways how to provide security in PDF documents. I conclude it should be provided a simple risks analysis before providing long-term archiving of PDF document. An organization also should take this analysis when creating its retention plan.
Security of an Electronic Voting System
Fritzová, Petra ; Růžička, Pavel (advisor) ; Joščák, Daniel (referee)
Electronic elections, also known as i-voting might help in removing the crisis in our democracy, which is reflected in non-cooperation in the opportunity of expressing their opinions during direct elections. Automation that is brought by i-voting process could mean reducing the risk of human error and also the risk of votes manipulation. On the other hand, the introduction of i-voting means the rise of new risks and vulnerabilities, which could attacker exploit to breach the security i-voting process. Thesis analyzes the Estonian electronic election system and system SERVE in terms of infrastructure and functionality of their components, identifies and suggests the basic possibilities of attacks on these systems. A special section is devoted to the electronic election system in Norway, where the cryptographic theory, which is the base for this system, was reviewed and the evidence that proofs the safety of this system was designed. Powered by TCPDF (www.tcpdf.org)
Security and usability of standard has hfunctions, in particular MD-5, SHA-1 and SHA-2
Galaczová, Barbora ; Tůma, Jiří (advisor) ; Joščák, Daniel (referee)
Title: Security and usability of standard hash functions, in particular MD-5, SHA-1 and SHA-2 Author: Galaczová Barbora Department: Department of Algebra Supervisor: Doc. RNDr. Tůma Jiří, DrSc., Department of Algebra Consultant: Ing. Budiš Petr, Ph.D. Abstract: In the present work we try to digestedly describe standard hash functions, in particular MD-5, SHA-1 and SHA-2. We describe resume of existing attacks on these hash functions. We closely focused on MD-5 collision attacks, because the other hash function collision attacks result from these. Next we describe posibilities of practical usage of hash function collisions, in particular into the qualified certificates area and possible threats. At the end to the present work we describe new hash functions, which could replace current hash functions. This work also contains software to calculate MD-5 hash and search it`s collisions. The software is based on method invented by Czech cryptoanalytist Vlastimil Klíma. Keywords: hash function, collision, qualified certificate, security.
Comparative study of current and new hash functions
Suchan, Martin ; Tůma, Jiří (advisor) ; Joščák, Daniel (referee)
The goal of this study is to present comparison of today's most widely used cryptographic hash functions and compare them with drafts of new hash functions, which are being currently developed for Advanced Hash Standard competition. This study also includes implementation of all described functions in programming language C#.
Trustworthiness (credibility) of provably secure cryptography
Barczi, Rudolf ; Joščák, Daniel (referee) ; Rudolf, Bohuslav (advisor)
In the present work we study provable security in the random oracle model and the standard model using the OAEP cryptosystem as an example. We begin with general introduction to public-key cryptography. In the next chapter we trace the evolution of RSA-OAEP cryptosystem security proofs in the random oracle model from the original controversial proof of security from 1994 to the correct and technically challenging one from 2004. The third chapter is dedicated to the selected problematic aspects of RSA-OAEP practical security. The goal of the extensive fourth chapter is to present some of the most recent results regarding the security of RSA-OAEP in the standard model. The rst result from 2009 shows the fundamental impossibility of security proof construction in the sense of CCA2. The result from 2006, despite being positive (weak non-malleability of fully-instantiated OAEP), is of an arguable signi cance. In the end we mention some comments on the state-of-the-art provable security of RSA-OAEP.
Searching collisions in hash functions
Joščák, Daniel
The main interest of this paper is finding collisions in the hash function MD5. We present our new algorithm based on Wangs et al. methods of finding collisions in MD5. While writing this thesis Stevens and Klima published their fast algorithms for finding collisions. We give a description of these algorithms and the calculation of computianal complexity of all three algorithms.
Searching collisions in hash functions
Joščák, Daniel ; Holub, Štěpán (referee) ; Tůma, Jiří (advisor)
The main interest of this paper is finding collisions in the hash function MD5. We present our new algorithm based on Wangs et al. methods of finding collisions in MD5. While writing this thesis Stevens and Klima published their fast algorithms for finding collisions. We give a description of these algorithms and the calculation of computianal complexity of all three algorithms.

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