Design and analysis of cryptographic algorithms

Abstract

In today’s world computers are ubiquitous. They can be found in virtually any industry and most households own at least one personal computer or have a mobile phone. Apart from these fairly large and complex devices, we also see computers on a much smaller scale appear in everyday objects in the form of micro-controllers and RFID chips.What truly transformed our society are large scale networks, like the Internet or mobile telephone networks, which can link billions of devices. Our ways of communicating and conducting business have severely changed over the last decades due to this development. However, most of this communication happens over inherently insecure channels requiring methods to protect our communication. A further issue is the vast amount of data generated, which raises serious privacy concerns.Cryptography provides the key components for protecting our communication. From securing our passwords and personal data to protecting mobile communication from eavesdroppers and our electronic bank transactions from manipulation. These applications would be impossible without cryptography. The main topic of this thesis is the design and security analysis of the most fundamental algorithms used in cryptography, namely block ciphers and cryptographic hash functions. These algorithms are the building blocks for a vast amount of applications and play a vital role in providing both confidentiality and integrity for our communication. This work is organized in two parts. First, an introduction to block ciphers and cryptographic hash functions is given to provide an overview over the state-of-the-art, the terminology, and how we can evaluate the security of an algorithm. The second part is a collection of scientific publications that have been written during the PhD studies and published. In the first publication we analyze the security of cryptographic hash functions based on the AES and demonstrate practical attacks on reduced-round versions of these algorithms. The second publication provides cryptanalysis of the lightweight block cipher SIMON in particular how resistant this type of block ciphers are against differential and linear cryptanalyis. In the fourth publication we present a short-input hash function utilizing AES-specific instructions on modern CPUs in order to improve the performance of hashbased signature schemes. The last publication deals with the design of the tweakable lightweight block cipher Skinny which provides strong security bounds against differential and linear attacks while also competing with the performance of SIMON