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Hash Function Design Using Genetic Programming
Michalisko, Tomáš ; Piňos, Michal (referee) ; Sekanina, Lukáš (advisor)
This thesis deals with automated design of hash functions using Cartesian genetic programming. The chosen method for collision resolution is cuckoo hashing. Three variants of hash function encodings were compared. Experiments were performed with datasets containing network flows. The most suitable parameters of CGP, including the function set, were determined. The best evolved hash functions achieved comparable results to the functions designed by experts. The main finding is that hash functions consisting of 64-bit operations achieve the best results.
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Implementation of modern hash functions
Trbušek, Pavel ; Sobotka, Jiří (referee) ; Stančík, Peter (advisor)
Master's thesis analyses modern hash functions. The requirements for these features and briefly outlined some of the types of attacks are given in the first part. The second part focuses on the specication Skein hash function, which is among the candidates for the new SHA-3 standard, and a description of the JCOP platform, which is a function implemented. In the last part of the work there are discussed implementation problematic parts and evaluation of the selected solution.
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Password deposition techniques in operating systems
Pavlík, Martin ; Růčka, Lukáš (referee) ; Hajný, Jan (advisor)
This master thesis deals with ways to store passwords in current operating systems. Specifically, this work focuses on Windows, Linux, BSD and OS X. These systems are examined for ways of hashing passwords and on resistance of resulting hashes against various attacks. First (theoretical) section describes the procedures and algorithms that are needed for user authentication. This part also describes methods of hash storing. At the end of the theoretical part are generally described some possible attacks against hash functions. In second (practical) part is described and tested tools for obtaining hashes of the investigated operating systems. Subsequently practical attacks were conducted against obtained hashes by using appropriate tools. Furthermore there are presented results of the attacks. In the conclusion of the work there is a comparison of tools and methods which were used to obtain plaintext passwords from operating systems.
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Evolutionary Design of Hash Functions
Kidoň, Marek ; Bidlo, Michal (referee) ; Dobai, Roland (advisor)
Hash tables are fast associative array implementations which became part of modern world of information technology and thanks to its simplicity became very popular among computer programmers. The choice of proper hash function is very important. Improperly selected hash function can result in poor hash table performance and its application. Currently there are many exceptional implementations of general hash functions. Such functions are not constrained to a concrete set of inputs, they perform on any input. On the other hand if we know the input domain we can design a specific hash function for desired application thus reaching better levels of performance compare to a general hash function. However hash function design is not trivial. There are no rules, standards, guides nor automated tools that would help us with such a task. In case of manual design the hash function author has to rely on his/her knowledge, experience, inventiveness and intuition. In case of such complicated tasks there is sometimes advantageous to choose a different path and use techniques such as evolution algorithms. Natural computing is an approach of certain problem solutions that are inspired by the process of species reproduction as defined by Charles Darwin. In this thesis we will design hash functions for the domain of IP addresses, that serve as an unique network device interface identifier in internet protocol networks. The chosen subset of natural computing is the genetic programming, a very specific technique that is an adequate approach to our problem thanks to its properties. Evolutionary designed hash functions offer good properties. They outperform state-of-the-art generic, human-created hash functions in terms of speed and collision resistance.
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Neural networks in cryptography
Borkovec, Tomáš ; Rášo, Ondřej (referee) ; Martinásek, Zdeněk (advisor)
Bachelor's thesis aims to introduce neural networks and their properties, which can be used for creating cryptographic protocols based on neural networks. It proposed concrete use of neural networks in cryptography and creates a teoretical basis for the practical implementation. In practical section is discusses the creation of neural network on which we based cryptographic model. The constructed models are then subjected to testing. At the close of the thesis we discussed the advantages and disadvantages of possible use in real cryptographic modules.
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Secured access for web applications
Humpolík, Jan ; Pelka, Tomáš (referee) ; Doležel, Radek (advisor)
This thesis mainly concerns often neglected security part of each web application, but also secure access users themselves. Describes theoretically and practically modern security technology, on a web application being tested and shows a possible way of defense. Gives instructions for installing its own web server.
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Hash functions - characteristics, implementation and collisions
Karásek, Jan ; Sobotka, Jiří (referee) ; Lambertová, Petra (advisor)
Hash functions belong to elements of modern cryptography. Their task is to transfer the data expected on the entry into a unique bite sequence. Hash functions are used in many application areas, such as message integrity verification, information authentication, and are used in cryptographic protocols, to compare data and other applications. The goal of the master’s thesis is to characterize hash functions to describe their basic characteristics and use. Next task was to focus on one hash function, in particular MD5, and describe it properly. That means, to describe its construction, safety and possible attacks on this function. The last task was to implement this function and collisions. The introductory chapters describe the basic definition of hash function, the properties of the function. The chapters mention the methods preventing collisions and the areas were the hash functions are used. Further chapters are focused on the characteristics of various types of hash functions. These types include basic hash functions built on basic bit operations, perfect hash functions and cryptographic hash functions. After concluding the characteristics of hash functions, I devoted to practical matters. The thesis describes the basic appearance and control of the program and its individual functions which are explained theoretically. The following text describes the function MD5, its construction, safety risks and implementation. The last chapter refers to attacks on hash functions and describes the hash function tunneling method, brute force attack and dictionary attack.
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Hash Function Design Using Genetic Programming
Michalisko, Tomáš ; Piňos, Michal (referee) ; Sekanina, Lukáš (advisor)
This thesis deals with automated design of hash functions using Cartesian genetic programming. The chosen method for collision resolution is cuckoo hashing. Three variants of hash function encodings were compared. Experiments were performed with datasets containing network flows. The most suitable parameters of CGP, including the function set, were determined. The best evolved hash functions achieved comparable results to the functions designed by experts. The main finding is that hash functions consisting of 64-bit operations achieve the best results.
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Analysis of the CubeHash proposal
Stankovianska, Veronika ; Tůma, Jiří (advisor) ; Hojsík, Michal (referee)
The present thesis analyses the proposal of CubeHash with spe- cial emphasis on the following papers: "Inside the Hypercube" [1], "Sym- metric States and Their Improved Structure" [7] and "Linearisation Frame- work for Collision Attacks" [6]. The CubeHash algorithm is presented in a concise manner together with a proof that the CubeHash round function R : ({0, 1}32 )32 → ({0, 1}32 )32 is a permutation. The results of [1] and [7] con- cerning the CubeHash symmetric states are reviewed, corrected and substan- tiated by proofs. More precisely, working with a definition of D-symmetric state, based on [7], the thesis proves both that for V = Z4 2 and its linear subspace D, there are 22 |V | |D| D-symmetric states and an internal state x is D-symmetric if and only if the state R(x) is D-symmetric. In response to [1], the thesis presents a step-by-step computation of a lower bound for the num- ber of distinct symmetric states, explains why the improved preimage attack does not work as stated and gives a mathematical background for a search for fixed points in R. The thesis further points out that the linearisation method from [6] fails to consider the equation (A ⊕ α) + β = (A + β) ⊕ α (∗), present during the CubeHash iteration phase. Necessary and sufficient conditions for A being a solution to (∗) are...
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Kombinatorika hashovacích funkcí
Sýkora, Jiří ; Holub, Štěpán (advisor) ; Šaroch, Jan (referee)
In this thesis, we study hash functions. We focus mainly on the famous Merkle-Damg˚ard construction and its generalisation. We show that even this generalised construction is not resistant to multicollision attacks. Combinatorics on words plays a fundamental role in the construction of our attack. We prove that regularities unavoidably appear in long words with bounded number of symbol occurences. We present our original results concerning regularities in long words. We lower some earlier published estimates, thus reducing the comlexity of the attack. Our results show that generalised iterated hash functions are interesting rather from the theoretical than practical point of view. 1
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