Matthias Himmelmann – författare

Document from the year 2016 in the subject Mathematics - Number Theory, grade: 1,7, Free University of Berlin (Fachbereich fur Mathematik und Informatik), course: Kryptografie Seminar, language: English, abstract: In this discourse, I introduce the reader to the concept of Chosen-Plaintext Attacks, by first defining them and then introducing to some of the properties of encryption schemes secure against Chosen-Plaintext attacks. I then introduce the concept of pseudorandom functions and try to show, how pseudorandom functions or permutations help understanding CPA-security. The discourse ends with constructing a CPA-secure encryption scheme based on pseudorandom permutations and a proposition that proves its correctness.

Document from the year 2017 in the subject Mathematics - Geometry, grade: 2,0, University of Oslo, course: MAT4510 - Geometric Structures, language: English, abstract: Prepare to have your understanding of geometry challenged! This captivating exploration delves into the fascinating world of hyperbolic geometry, a non-Euclidean realm where parallel lines diverge and the angles of a triangle sum to less than 180 degrees. Unveiling the secrets of the hyperbolic plane, this work meticulously constructs the concept of area within this intriguing space, utilizing both the upper half-plane model (H) and the Poincare disk model (D). Discover how area, defined through the limit of Euclidean rectangles adapted to hyperbolic lengths, remains invariant under Mobius transformations, a crucial property for simplifying complex calculations. The heart of this investigation lies in the derivation of a remarkable formula for the area of a hyperbolic triangle, revealing its dependence solely on the triangle's angles - a stark contrast to Euclidean geometry. Journey further into the realm of hyperbolic trigonometry, where familiar trigonometric functions give way to their hyperbolic counterparts: sinh(t), cosh(t), and tanh(t). Explore the intricate relationships between these functions and witness the emergence of the hyperbolic Law of Cosines and the hyperbolic Pythagorean theorem, profound adaptations of classical trigonometric results. This book provides a rigorous and insightful journey into the core concepts of hyperbolic geometry, offering a blend of theoretical development and practical application. Ideal for students and researchers alike, this exploration provides a solid foundation in hyperbolic area calculation, hyperbolic triangle properties, and the fundamental principles of hyperbolic trigonometry. Uncover the beauty and elegance of a geometry that defies intuition and opens up new vistas in mathematical understanding, a rigorous and insightful journey into hyperbolic space. Explore the non-Euclidean properties of the Poincare disk and upper half-plane models as the text builds towards the derivation of the area formula, AH(ABC) = p - a - b - c, a cornerstone of hyperbolic geometry. Delve into the definitions of hyperbolic functions and their use in developing the hyperbolic Law of Cosines: cosh(a) = cosh(b)cosh(c) - sinh(b)sinh(c)cos(a), and the elegant hyperbolic Pythagorean theorem, cosh(a) = cosh(b)cosh(c), for right-angled triangles. This investigation offers a comprehensive introduction to hyperbolic geometry, unlocking the secrets of area, triangles, and trigonometry in this captivating alternative geometric space.