Selected Topics in Cryptography

Although a remarkable science, cryptography is also an art and a puzzling game. We have to think as an attacker would, while defending systems against threats: juggling between speed, usability and security, twisting known concepts in order to make them fit our scope, designing high level concepts, while keeping in mind the low level ones and so on. Influenced by the plethora of concepts a cryptographer has to manage, in this work we touch on various areas of cryptography and we either take the role of the designer or of the attacker. By presenting both sides of the same coin, we wish that the reader will start appreciating the beauty of this puzzling science and will begin to see the relationships that arise between seemingly different concepts.