|
|
Searching optimal strategies for the number field sieve
Perůtka, Lukáš ; Růžička, Pavel (referee) ; Drápal, Aleš (advisor)
In this work we study the number field sieve algorithm. Our main focus is on its theoretical background. We present all important theorems which are needed for a full understanding of the algorithm. We also describe the most widely used implementation of the parts of the algorithm and we discuss in which situation they should be used. At the end we show results from measurements of sieving phase on the implementation which was written for our Department of Algebra.
|
|
|
Quasigroup based cryptography
Frisová, Andrea ; Drápal, Aleš (referee) ; Stanovský, David (advisor)
In this work, we study some properties of an in nite matrix, which consists of quasigroup elements. This matrix is generated from a certain sequence X using left iterated translations. We suppose that the sequence X is periodic and we examine how the periods of the rows of our matrix behave for various types of quasigroups. We show that for central quasigroups the periods increase at most linearly. Further, we try to apply our result to the stream cipher Edon-80.
|
|
|
Quasigroups, one-way functions and hash mappings
Machek, Ivo ; Stanovský, David (referee) ; Drápal, Aleš (advisor)
In the rst part of this work we study the complexity of solving nonlinear quasigroup equations for di erent classes of quasigroups. In particular we study the application of principle of central quasigroups on the blocks of congruence. We show that these quasigroups can be shapeless and therefore we gain counterexample to the hypothesis which was stated by D. Gligoroski. In the second part of this work we apply previous results on the concrete quasigroups of the type Edon-R-I,II and we deduce the complexity of the corresponding algorithm for inverting the hash function Edon-R.
|
|
| |
|
|
Cryptanalysis of AES
Botka, Michal ; Drápal, Aleš (referee) ; Tůma, Jiří (advisor)
In the present work we study a security of the AES cipher. We concern in a mathematical representation of a block cipher and how to use it to algebraic attacks. We show a summary of known algorithms which are useful for these attacks. We show how to convert problem of solving the system of polynomial equations to SAT problem and we describe how SAT solvers work.
|
|
|
Reed-Solomon codes and applications
Horal, Pavel ; Vojtěchovský, Petr (referee) ; Drápal, Aleš (advisor)
Xazev praee: Reed-Solomonovy kody a jejich aplikaco Autor: Pavel Iloral Katcdra (ustav): Katedra Algebry Vedouci bakalafsko prace: Doc. RNDr. Ales Drapal. CSc. c-nia.il vedoiiciho: drapar^karlin.mil', cuni.cz Abstrakt: Prace podava ucelenon definici klasiekyeh Reed-Solomonovych kodn, vcetne potfobuyeh zakladu tcxjric1 k()du. Je dokazana cykliciiost RS kodn delky q - I . Na cyklienosti jsou pak zalozeny tri inx'zontovane dekcklovac'i algoritmy fPetersonnv, Rorlrkain])-Mas.seyuv a Enklidi'iv dekodova.ci algoritmns), vcetne. dukazfi existcniee feseni. V ])oslodni ka])itole uvadiin nckolik a.]>likaci RS kodu, vcetne nejznainejyiho standardu CIRC' pouzivancho na Imdebnich CD. Klieova alova: .s;nnoo])ravny k(5d.1'X'C, Reed-Solomon. Pcterstm, Berlekanip-Massey. Euklid. CIRC1 Title: Rood-Solomon codes and applications Author: Pavel llora.1 Department: Department of Algebra Supervisor: Doc. HXDr. Ales Drapal, CSc. Supervisor's e-mail address: drapal (fkarlin.nirl.ouni.c/ Alislracl: This work presents compact definition of classic Heed-Solomon codes with necessary elements of coding theory. The ryclicity of RS codes of length q - 1 is prooved and there are comletely described three decoding algorithms (Peterson's, Berlekamp-Ma,ssoy and Euclid decoding algorithm) based on RS cyclirity. I also in- troduce a few RS...
|
|
| |
|
|
Optimal strategy for factorizing smaller composite integers
Kadlček, Tomáš ; Kechlibar, Marian (referee) ; Drápal, Aleš (advisor)
Nazpv prace: Opt.inialni strategic faktorizaoe moiisicl) slozenych ciscl Autor: TomaM Kadlcok Katedra. (ust.av): Katcdra algebry Vedouci bakalafske prace: Doc. RNDr. Ales Drapal, CSc. (vnia.il vodouciho: Ales.DrapaH'iJmff.cuni.cz Abstrakt: Cilein prace bylo tostovat tfi algoritiny implementovane v kva.dratic.kom situ, ktereje vefojno k dispo/ici na wcbovych strankach katedry algobry MFF (/dc [3]). .Tojich ukolcm v ranici algorit.mu MPQS/SIQS jo rozkladat kladna cisla na cisla fadu nojvyse unsigned int (v C I I ). tj. do 32 l)itn delky vcctne. Tat.o chmost jo mitna pfi spnst.oni variant}- double large prime variation (DLPV), kdy rozkladainc oisla. ktora so tie zi'ela ro/lo/ila do faktori/arni Ita/e. AlgoriUny dostnpno pro tos- tovani byly: Pollard /), Pollard p - 1 a C'FHAC. Motoda oliptiokych kfivok neljyla dosud implemontovaiia. Porovna\;'nii inotod bylo provedeno na nekolika odli.snyeh pocitacich. Vysledkem i)lynonciin /, nioreni je lakt, '2v. ]>ro roxkladani ci.sel delsich no/ 70 cifor s pou/.itim varianty ULPV jo nojvhodnejsi nojdfivo spnstit /; - 1 algo- ritnms a pokud v ro/kladani nenspeje, pak joj dojilnit algoritnuun p nebo CFRAC. Zrychloni ooloho algoritniu x,|)nsobouo tiinto optiinalixovanym dilcini rozkladanini so pohybnje v facln 5-10%. Klic'ova slova: Pollard (>, Pollard p - \, CFH.AC!,...
|
|
|
The stream cipher RC4
Hojsík, Michal ; Kortelainen, Juha (referee) ; Drápal, Aleš (advisor)
In the present work we study a class of generalised inner states of the cipher RC4, the so-called persistent states. The RC4 stream cipher is the most widely used software-based stream cipher and the existence of such a state would be a significant weakness of the cipher. We describe the Tabular model and using the model we prove the periodicity of these states. Then we study a new type of relationship between the tabular model and the equivalences on linearly ordered sets and we prove the regularity of the matrix determined by such an equivalence. Afterwards we apply the obtained result to the theory of persistent states and we prove that there exists no reachable persistent k-state for k equal to 2, 3, 4 in the specific case. Moreover, we present some new unreachable persistent states. Finally, we indicate the cryptanalytical significance of the persistent states.
|
|
|
Modification of electroinsulating varnish with ground mica
Drápal, Aleš ; Frk, Martin (referee) ; Rozsívalová, Zdenka (advisor)
This master's thesis focuses on composite systems based on varnish combined with different filler ratios of micronized mica. The aim is to analyse impact of the filler on dielectric properties of the varnish, i.e. relative permittivity and loss factor as functions of frequency as well as charging and discharging currents as functions of time. Dielectric mixture formulas are applied on relative permittivity values. Calculated and measured values are compared.
|
guest ::
