  Mobile communication touches every aspect of our life, it become one of the
major dependencies that the 21st Century civilizations rely on. Thereby,
security is a major issue that should be targeted by communication
technologies. In this paper we will target authentication and encryption in GSM
and 3G/UMTS. In order to understand clearly how things work, we will start by
presenting the architecture of each network, its major components, its
authentication algorithms, protocols used, and KASUMI Block Cipher.
