Dissertations / Theses on the topic 'Quasigroup'

We investigate power graphs of quasigroups. The power graph of a quasigroup takes the elements of the quasigroup as its vertices, and there is an edge from one element to a second distinct element when the second is a left power of the first. We first compute the power graphs of small quasigroups (up to four elements). Next we describe quasigroups whose power graphs are directed paths, directed cycles, in-stars, out-stars, and empty. We do so by specifying partial Cayley tables, which cannot always be completed in small examples. We then consider sinks in the power graph of a quasigroup, as subquasigroups give rise to sinks. We show that certain structures cannot occur as sinks in the power graph of a quasigroup. More generally, we show that certain highly connected substructures must have edges leading out of the substructure. We briefly comment on power graphs of Bol loops.

A monogenic quasigroup is one generated by a single element, and as such is not just non-associative but in general non power associative. We show that monogenic quasigroups or loops with various specified characteristics can exist, by demonstrating constructions and by giving examples. This often involves completing an associated partial latin square, or demonstrating that a completion is possible. It is shown that for every order n ≥ 4 there are monogenic quasigroups generated by each of any m ≤ n of their elements, and similarly for monogenic loops (n ≥ 6 , 2 ≤ m ≤ n −1). Any element in a quasigroup must have its powers unambiguous and distinct (called good) up to some degree j ≥ 2, and unambiguous but not necessarily distinct (called clear) up to some degree k ≥ j. The conditions for the existence of a quasigroup of order n having a generator with a good j th and clear k th power are determined. A monogenic quasigroup may be said to be g-good if every element has a good g th power. An algorithm for finding examples based on diagonally cyclic latin squares is developed, and a computer program used to find comprehensive solutions for g ≤ 16 and odd orders n ≤ 95 (and patchily to g = 17, n = 111), with particular reference to the lowest n affording a solution for any g. A maximally non power associative quasigroup has every element with all its bracketings up to some length distinct. A diagonally cyclic quasigroup of order 23 with all 23 products of length ≤ 5 distinct for every element is displayed,as is one of order 63 with 63 of the 65 bracketings up to length 6 distinct for each element. Properties of direct products of monogenic quasigroups, and the significance of parastrophy and isotopy, are considered. The existence or not of monogenic versions of particular types of quasigroups and loops (for example, totally symmetric, inverse property, entropic, Bol and Moufang, among others) is also explored.

The notion of a Hopf algebra has been generalized many times by weakening certain properties; we introduce Hopf quasigroups which weaken the associativity of the algebra. Hopf quasigroups are coalgebras with a nonassociative product satisfying certain conditions with the antipode re ecting the properties of classical inverse property quasigroups. The de nitions and properties of Hopf quasigroups are dualized to obtain a theory of Hopf coquasigroups, or `algebraic quasigroups'. In this setting we are able to study the coordinate algebra over a quasigroup, and in particular the 7-sphere. One particular class of Hopf quasigroups is obtained by taking a bicrossproduct of a subgroup and a set of coset representatives, in much the same way that Hopf algebras are obtained from matched pairs of groups. Through this construction the bicrossproduct can also be given the structure of a quasi-Hopf algebra. We adapt the theory of Hopf algebras to Hopf (co)quasigroups, de ning integrals and Fourier transformations on these objects. This leads to the expected properties of separable and Frobenius Hopf coquasigroups and notions of (co)semisimplicity.

Probleme: soit g un groupe abstrait, est-il possible de construire un quasigroupe dont le groupe de multiplication est isomorphe a g? une reponse negative sera apportee pour les groupes hamiltoniens, de heineken-mohamed, des quaternions generalises et dicycliques d'ordre 4n. Une reponse positive sera apportee pour les groupes symetriques, alternes, diedraux, les groupes de mathieu de degre 11, 12 et 23, les groupes lineaires generaux et projectifs lineaires, certains p-groupes (semi-diedraux,. . . ), les groupes de coxeter de type bn. Le probleme pose pouvant se ramener a l'etude des groupes de multiplication de boucles, l'auteur construira des boucles commutatives, a l'aide de leurs translations a gauche, dont le groupe de multiplication est isomorphe soit au groupe (4,4|2,,2n+1) de degre 4n+2, soit au groupe (2,4,4;n+1) de degre 4n+4. Nous montrerons que certains d'entre eux sont transitifs minimaux, i. E. Sans sous groupe propre transitif. D'autre part, une boucle commutative dont le groupe de multiplication est isomorphe au p-sous groupe de sylow du groupe symetrique d'ordre p#2 sera construite par l'intermediaire de sa table de multiplication. Enfin, il sera montre que si les groupes abeliens, de fischer decentres, alternes sont representables en groupe de multiplication d'une boucle, une telle representation n'existe pas pour les groupes diedraux, les groupes de frobenius, les groupes de permutations dont le stabilisateur d'un element est de cardinal 1, 2 ou 3

In this thesis I shall be exploring the normal and characteristic structure of quasigroups and loops. In recent years there has been a revival of interest in the theory of loops and in particular in the relationship between the properties of a loop and the properties of its multiplication group; and several powerful new theorems have emerged which allow the structural properties of a loop to be related to its multiplication group. I shall combine these ideas with tools developed at the beginning of loop theory to produce some interesting new theorems, principally relating the order of a finite multiplication group to the structure of its loop.

This thesis describes methods of secret communication based on latin squares and their close relative, quasigroups. Different types of cryptosystems are described, including ciphers, public-key cryptosystems, and cryptographic hash functions. There is also a chapter devoted to different secret sharing schemes based on latin squares. The primary objective is to present previously described cryptosystems and secret sharing schemes in a more accessible manner, but this text also defines two new ciphers based on isotopic latin squares and reconstructs a lost proof related to row-latin squares.
Denna uppsats beskriver kryptosystem och metoder för hemlighetsdelning baserade på latinska kvadrater och det närliggande konceptet kvasigrupper. Olika sorters chiffer, både symmetriska och asymmetriska, behandlas. Dessutom finns ett kapitel tillägnat kryptografiska hashfunktioner och ett tillägnat metoder för hemlighetsdelning. Huvudsyftet är att beskriva redan existerande metoder för hemlig kommunikation på ett mer lättillgängligt sätt och med nya exempel, men dessutom återskapas ett, till synes, förlorat bevis relaterat till rad-latinska kvadrater samt beskrivs två nya chiffer baserade på isotopa latinska kvadrater.

Redes de sensores sem fio (RSSF) tipicamente consistem de nós sensores com limitação de energia, processamento, comunicação e memória. A segurança em RSSF está se tornando fundamental com o surgimento de aplicações que necessitam de mecanismos que permitam autenticidade, integridade e confidencialidade. Devido a limitações de recursos em RSSF, adequar criptossistemas de chaves públicas (PKC) para estas redes é um problema de pesquisa em aberto. Meados de 2008, Danilo Gligoroski et al. propuseram um novo PKC baseado em quase-grupos multivariados quadráticos (MQQ). Experimentos feitos por Gligoroski na plataforma FPGA mostram que MQQ executou em tempo menor que principais PKC (DH, RSA e ECC) existentes, tanto que alguns artigos afirmam que MQQ possui velocidade de uma típica cifra de bloco simétrica. Além disto, o MQQ exibiu o mesmo nível de segurança que outros PKC (DH, RSA e ECC) necessitando chaves menores. Outra propriedade que chama atenção no MQQ é o uso das operações básicas XOR, AND e deslocamento de bits nos processos de encriptação e decriptação, fato importante considerando que uma RSSF possui processamento limitado. Estas características tornam o MQQ promissor a levar um novo caminho na difícil tarefa de dotar redes de sensores sem fio de criptossistemas de chaves públicas. Neste contexto se insere este trabalho que analisa a viabilidade de implementar o algoritmo MQQ em uma plataforma de RSSF. Sendo importante considerar que este trabalho inova na proposta de levar para RSSF este novo PKC baseado quase-grupos multivariados quadráticos, além de contribuir com um método para reduzir o tamanho da chave pública utilizada pelo MQQ. Foram feitos testes com MQQ nas plataformas TelosB e MICAz, sendo que o MQQexibiu os tempos de 825; 1 ms para encriptar e 116; 6 ms para decriptar no TelosB e 445 ms para encriptar no MICAz.
Wireless sensor networks (WSN) typically consist of sensor nodes with limited energy, processing, communication and memory. Security in WSN is becoming critical with the emergence of applications that require mechanisms for authenticity, integrity and confidentiality. Due to resource constraints in sensor networks, public key cryptosystems suit (PKC) for these networks is an open research problem. In 2008 Danilo Gligoroski et al. proposed a new PKC based on quasi-groups multivariate quadratic (MQQ). Experiments by Gligoroski on FPGA platform show that MQQ performed in less time than most popular PKC (DH, RSA and ECC), so that some papers say MQQ has a typical speed of symmetric block cipher. Moreover, the MQQ exhibited same level of security that other PKC (DH, RSA and ECC) requiring keys minors. Another property that draws attention in MQQ is the use of basic operations XOR, AND, and bit shifting in the processes of encryption and decryption, important fact considering that a WSN has limited processing. These features make the MQQ promising to take a new path in the difficult task of providing wireless sensor networks in public key cryptosystems. Appears in this context that this study examines the feasibility of implementing MQQ a platform for WSN. Is important to consider this innovative work in the proposal to bring this new PKC for WSN based multivariate quadratic quasigroups, and contribute a method to reduce the size public key used by MQQ. Tests with MQQ on platforms TelosB and MICAz, the MQQ exhibited 825ms to encrypt and 116ms to decrypt on TelosB and 445 ms to encrypt on MICAz.

This thesis follows up the results of article A. Drápal a I. M. Wanless, On the number of quadratic orthomorphisms that produce maximally nonassociative quasigroups. This paper dealt with the density of maximally non-associative quasigroups of a certain cons- truction. However, certain cases had to be neglected in the calculations due to restrictive conditions. The examination of these cases is the subject of this work. It turned out that the asymptotic behavior in the general case as in the article differs from the beha- vior in cases examined in our work. In addition to the calculations themselves, the work contains a theoretical introduction with an explanation of the constructions used in the previous article, as well as our own theory necessary for our calculations. In addition, we experimentally verified our results. 1

It is well known that for any Steiner triple system (STS) one can define a binary operation · upon its base set by assigning x·x = x for all x and x·y = z, where z is the third point in the block containing the pair {x, y}. The same can be done for Mendelsohn triple systems (MTS), directed triple systems (DTS) as well as hybrid triple systems (HTS), where (x, y) is considered to be ordered. In the case of STSs and MTSs the operation yields a quasigroup, however this is not necessarily the case for DTSs and HTSs. A DTS or an HTS which induces a quasigroup is said to be Latin. The quasigroups associated with STSs and MTSs satisfy the flexible law x · (y · x) = (x · y) · x but those associated with Latin DTSs and Latin HTSs need not. A DTS or an HTS is said to be pure if when considered as a twofold triple system it contains no repeated blocks. This thesis focuses on the study of Latin DTSs and Latin HTSs, in particular it aims to examine flexibility, purity and other related properties in these systems. Latin DTSs and Latin HTSs which admit a cyclic or a rotational automorphism are also studied. The existence spectra of these systems are proved and enumeration results are presented. A smaller part of the thesis is then devoted to examining the size of the centre of a Steiner loop and the connection to...

We present the theory of selfdistributive quasigroups and the construction of non-affine selfdistributive quasigroup of size 216 that was presented by Onoi in 1970 and which was the least known example of such structure of size 2k . Based on this construction, we introduce the notion of Onoi structures and Onoi mappings between them which generalizes Onoi's construction and which allows us to construct non-affine selfdistributive quasigroups of size 22k for k ≥ 3. We present and implement algorithm for finding central extensions of self- distributive quasigroups which enables us to classify non-affine selfdistributive quasigroups of size 2k and prove that those quasigroup exists exactly for k ≥ 6, k ̸= 7. We use this algorithm also in order to better understand the structure of non-affine selfdistributive quasigroups of size 26 . 1

This thesis is concerned with quasigroups with a small number of associative triples. The minimum number of associative triples among quasigroups of orders up to seven has already been determined. The goal of this thesis is to determine the minimum for orders eight and nine. This thesis reports that the minimum number of associative triples among quasigroups of order eight is sixteen and among quasigroups of order nine is nine. The latter finding is rather significant and we present a construction of an infinite series of quasigroups with the number of associative triples equal to their order. Findings of this thesis have been a result of a computer search which used improved algorithm presented in this thesis. The first part of the thesis is devoted to the theory that shows how to reduce the search space. The second part deals with the development of the algorithm and the last part analyzes the findings and shows a comparison of the new algorithm to the previous work. It shows that new search program is up to four orders of magnitude faster than the one used to determine the minimum number of associative triples among quasigroups of order seven.