Selected Cryptographic Methods for Securing Low-End Devices

We consider in this thesis the security goals confidentiality of messages and authenticity of entities in electronic communication with special focus on applications in environments with restricted computational power, e.g., RFID-tags or mobile phones. We introduce the concept of stream ciphers, describe and analyze their most important building blocks, analyze their security features, and indicate ways to improve their resistance against certain types of attacks. In the context of entity authentication, we describe special protocols based on randomly choosing elements from a secret set of linear vector spaces and relate the security of these protocols to the hardness of a certain learning problem

On Lower Bounds for Parity Branching Programs

Diese Arbeit beschaeftigt sich mit der Komplexität von parity Branching Programmen. Es werden superpolynomiale untere Schranken für verschiedene Varianten bewiesen, nämlich für well-structured graph-driven parity branching programs, general graph-driven parity branching programs und Summen von graph-driven parity branching programs