Computing a Gröbner basis of a polynomial ideal over a Euclidean domain

AbstractAn algorithm for computing a Gröbner basis of a polynomial ideal over a Euclidean domain is presented. The algorithm takes an ideal specified by a finite set of polynomials as its input; it produces another finite basis of the same ideal with the properties that using this basis, every polynomial in the ideal reduces to 0 and every polynomial in the polynomial ring reduces to a unique normal form. The algorithm is an extension of Buchberger's algorithms for computing Gröbner bases of polynomial ideals over an arbitrary field and over the integers as well as our algorithms for computing Gröbner bases of polynomial ideals over the integers and the Gaussian integers. The algorithm is simpler than other algorithms for polynomial ideals over a Euclidean domain reported in the literature; it is based on a natural way of simplifying polynomials by another polynomial using Euclid's division algorithm on the coefficients in polynomials. The algorithm is illustrated by showing how to compute Gröbner bases for polynomial ideals over the integers, the Gaussian integers as well as over algebraic integers in quadratic number fields admitting a division algorithm. A general theorem exhibiting the uniqueness of a reduced Gröbner basis of an ideal, determined by an admissible ordering on terms (power products) and other conditions, is discussed

On Factorized Gröbner Bases

We report on some experience with a new version of the well known Gröbner algorithm with factorization and constraint inequalities, implemented in our REDUCE package CALI, [12]. We discuss some of its details and present run time comparisons with other existing implementations on well splitting examples

Efficient computation of regular differential systems by change of rankings using Kähler differentials

We present two algorithms to compute a regular differential system for some ranking, given an equivalent regular differential system for another ranking. Both make use of Kähler differentials. One of them is a lifting for differential algebra of the FGLM algorithm and relies on normal forms computations of differential polynomials and of Kähler differentials modulo differential relations. Both are implemented in MAPLE V. A straightforward adaptation of FGLM for systems of linear PDE is presented too. Examples are treated

Efficient computation of regular differential systems by change of rankings using Kähler differentials

We present two algorithms to compute a regular differential system for some ranking, given an equivalent regular differential system for another ranking. Both make use of Kähler differentials. One of them is a lifting for differential algebra of the FGLM algorithm and relies on normal forms computations of differential polynomials and of Kähler differentials modulo differential relations. Both are implemented in MAPLE V. A straightforward adaptation of FGLM for systems of linear PDE is presented too. Examples are treated

Computations involving differential operators and their actions on functions

The algorithms derived by Grossmann and Larson (1989) are further developed for rewriting expressions involving differential operators. The differential operators involved arise in the local analysis of nonlinear dynamical systems. These algorithms are extended in two different directions: the algorithms are generalized so that they apply to differential operators on groups and the data structures and algorithms are developed to compute symbolically the action of differential operators on functions. Both of these generalizations are needed for applications

Gröbnerovy báze v kryptografii

Předložené práce studuje využití Grobnerových bází v kryptografii, a to speciálně při kryptoanalýze blokový šifer. Nejprve seznamujeme se základními pojmy teorie Grobnerových bází a metodou pro jejich nalezení, kterou je Buchbergerův algoritmus. Je vysvětlen princip řešení soustav polynomiálních rovnic pomocí vhodných Grobrenových bází. Následně je věnována pozornost moderním algoritmům pro nalezení Grobnerovy báze, jež Buchbergerův algoritmus vylepšují. V poslední části jsou shrnuty dosavadní výsledky dosažené v kryptografii pomocí metod založených na Grobnerových bázích a je představen pojem algebraické kryptoanalýzy. Ta převádí problém prolomení kryptosystému na problém nalezení řešení soustavy polynomiálních rovnic nad konečným tělesem. Na příkladech je vysvětleno jak konstruovat soustavy polynomů více proměnných popisující blokové šifry a jsou prezentovány výsledky praktických pokusů s takovými soustavami.The thesis focuses on the use of GrÄobner bases in cryptography and especially on applications in cryptanalysis of block ciphers. Some elementary concepts from the theory of GrÄobner bases are introduced together with Buchberger's algorithm, a method for constructing such bases. The principle of solving of poly nomial systems using suitable GrÄobner bases is explained. This is followed by pre sentation of modern algorithms that improve the Buchberger's algorithm. In the last part of the thesis present results achieved by GrÄobner bases are summarised and the notion of algebraic cryptanalysis is introduced. In algebraic cryptanalysis we transform breaking of given cryptosystem into a problem of solving polynomial equations over some nite eld. Examples of polynomial descriptions of block ciphers are provided together with some experimental result on arising polynomial systems.Department of AlgebraKatedra algebryFaculty of Mathematics and PhysicsMatematicko-fyzikální fakult