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An attack upon Wieschebrink's version of Niederreiter system
Homer, Miloslav ; Drápal, Aleš (advisor) ; Žemlička, Jan (referee)
In this work an attack upon Wieschebrink's version of Niederreiter cryptosystem using GRS codes by Couvreur et. al. from 2014 is described. Relevant notions of error-correcting code theory are presented, definitions of McEliece scheme, Niederreiter scheme and their respective Wieschebrink's modifications are shown. A description of the attack using distinguisher as described by Couvreur et. al. Based on componentwise code products and shortened codes properties follows, as does Sidelnikov-Shestakov attack on Niederreiter scheme with relevant group theory notions. Implementation details are also outlined. The attack is then summarized and its complexity is mentioned. The attack duration measured by the C++ implementation is presented in the last chapter. The program implementing the cryptosystem as well as the attack is located in the appendix with the program documentation. Powered by TCPDF (www.tcpdf.org)
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Minder's structural attack upon Sidelnikov's cryptosystem
Steinhauser, František ; Drápal, Aleš (advisor) ; Žemlička, Jan (referee)
After Sidelnikov proved in 1992 that the cryptosystem of Niederreiter is vulnera- ble, he designed his own cryptosystem in 1993. This new cryptosystem was based on McEliece schema, it was to be resistant to quantum computers and faster than McEliece cryptosystem. However, in 2007, Minder and Shokrollah proposed an attack proving that the cryptosystem of Sidelnikov was vulnerable as well. This thesis uses several well-known and several new theorems to describe algebraic characteristics of the Reed-Muller code, especially from the affinity point of view. It proves that the attack proposed by Minder and Shokrollah really breaks the cryptosystem of Sidelnikov. Implementation of this attack in C/C++ language is presented in the conclusion of the thesis along with a table of duration of this attack on a personal computer.
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Tests for generators of pseudorandom numbers
Jurečková, Olha ; Příhoda, Pavel (advisor) ; Žemlička, Jan (referee)
In this work we focus on tests for generators of pseudorandom bits. Generators of pseudorandom bits are one of the most important cryptographic tools. In the first part of this work we introduce statistical theory related for randomness testing. Then we present some basic definitions and facts from cryptography. In the second part of the work we describe ten different statistical tests and their modifications. We also present results of tests performed on Decim stream cipher, Geffe generator and Blum Blum Shub generator. 1
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Problém realizace von Neumannovsky regulárních okruhů
Mokriš, Samuel ; Růžička, Pavel (advisor) ; Žemlička, Jan (referee)
Title: The realization problem for von Neumann regular rings Author: Samuel Mokriš Department: Department of Algebra Supervisor of the master thesis: Mgr. Pavel Růžička, Ph.D., Department of Algebra Abstract: With every unital ring R, one can associate the abelian monoid V (R) of isomor- phism classes of finitely generated projective right R-modules. Said monoid is a conical monoid with order-unit. Moreover, for von Neumann regular rings, it satisfies the Riesz refinement property. In the thesis, we deal with the question, under what conditions an abelian conical re- finement monoid with order-unit can be realized as V (R) for some unital von Neumann regular ring or algebra, with emphasis on countable monoids. Two generalizations of the construction of V (R) to the context of nonunital rings are presented and their interrelation is analyzed. To that end, necessary properties of rings with local units and modules over such rings are devel- oped. Further, the construction of Leavitt path algebras over quivers is presented, as well as the construction of a monoid associated with a quiver that is isomorphic to V (R) of the Leavitt path algebra over the same quiver. These methods are then used to realize directed unions of finitely generated free abelian monoids as V (R) of algebras over any given field. A method...
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Multivariate cryptography
Jančaříková, Irena ; Žemlička, Jan (advisor) ; Růžička, Pavel (referee)
This thesis deals with multivariate cryptography. It includes specifically a description of the MQ problem and the proof of it's NP-completness. In the part of the MQ problem there is a description of a general pattern for the creation of the public part of asymetric cryptosystems based on the MQ problem. It this part the thesis describes the QMLE problem, which is important for the figure of the cryptosystem private key based on the MQ problem. Further, the thesis includes a description of the influence of the structure display, which appears in the QMLE problem, on time solution complexity of QMLE problem. The influence of time complexity has been detected by means of experimental measurement with programed algorithm. At the end of the thesis there is specified description of selected multivariety cryptosystems based on the MQ problem. Selected cryptosystems are provided with detailed description of encryption and decryption by means of selected cryptosystems and time estimations of these operations. The thesis includes estimations of memory requirements on saving of private and public key of the selected cryptosystems. Powered by TCPDF (www.tcpdf.org)
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Variants of knapsack cryptosystems
Kučerová, Michaela ; Příhoda, Pavel (advisor) ; Žemlička, Jan (referee)
The topic of this thesis is a cryptosystem, precisely a public key encryption scheme, that is based on the knapsack problem. At first we formulate terms like \mathcal{NP} -complete problem, one-way function, hard-core predicate, public key encryption scheme and semantic security which we connect in this thesis. After that we present the knapsack problem. Then we prove that the knapsack problem with appropriate parameters has a property that leads to semantic security of the encryption scheme which we present afterwards. This public key encryption scheme is based on the scheme proposed by Vadim Lyubashevsky, Adriana Palacio and Gil Segev. Powered by TCPDF (www.tcpdf.org)
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Structure of division rings
Reichel, Tomáš ; Žemlička, Jan (advisor) ; Šaroch, Jan (referee)
This bachelor thesis deals with a theorem and its proof, which allows construction of division ring from cyclic field extension which satisfies certain conditions. The reader is expected to have basic knowledge of linear algebra, ring and module theory. For using this theorem the reader also needs some skills in counting Galois groups. In this work there are also included two basic examples of usage the theorem. During the proof we introduce a structure of tensor product and Brauer group. Powered by TCPDF (www.tcpdf.org)
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Decidability of the theory of commutative groups
Čech, František ; Šaroch, Jan (advisor) ; Žemlička, Jan (referee)
In this thesis will be demonstrated proof of decidability of theory of commu- tative groups. This result was already shown in year 1955 by author W.Szmielew. However proof shown here takes different path. Result will by shown with use of results from theory of modules and theory of modeles prooved in article by M. Ziegler Model theory of modules. Final part of proof follows proof shown in article The elementary theory of Abelian groups by P. C. Eklofa and E. R. Fishera. 1
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Varieties of superalgebras
Lišková, Adéla ; Žemlička, Jan (advisor) ; Barto, Libor (referee)
The goal of the thesis is to introduce the basics of the theory of superalgebras, that is Z2-graded algebras over a field of characteristic different from two, as well as to present necessary basics of universal and multilinear algebra, especially the tensor product and the terms variety of algebra and ideal of identities. We present the definitions of algebra and superalgebra including examples, we then look into the tensor product of superalgebras and its properties, Clifford and Grassmann superalgebras. A part of the thesis is dedicated to the construction of the free nonassociative algebra and the clarification of the relationship between varieties of algebras and ideals of identities including the specification of said relationship for superalgebras. The thesis also deals with varieties of superalgebras. 1
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Lucas-Lehmer test
Vejpustek, Ondřej ; Holub, Štěpán (advisor) ; Žemlička, Jan (referee)
The aim of this thesis is to explain quadratic number field theory and prove correctness of the Lucas-Lehmer primality test. A quadratic number field is a field of the form Q( √ m). Chapter one describes elementary properties of such field's ring of integers focusing on characterisation of the ring's group of units. Chapter two studies ideal factorisation in this ring. It contains proofs of a theorem on unique factorisation of the ideals into prime ideals and a theorem describing all prime ideals. Chapter three employs quadratic number field theory to prove correctness of the Lucas-Lehmer prime test, which is a deterministic primality test for numbers of the form 2p − 1. 1
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