Design and Cryptanalysis of Symmetric Key Algorithms (Ontwerp en cryptanalyse van symmetrische-sleutel algorithms)

This thesis deals with symmetric-key algorithms and more specifically block ciphers and hash functions. The first set of results applies recent cryptanalysis methods (such as boomerang attacks and rebound attacks) to various algorithms. The second topic is the study of the differential probability of AES-like block ciphers for a fixed key. Finally, the design of a new lightweight algorithm is described.Differential cryptanalysis is one of the most powerful cryptanalysis techniques: it has not only been applied successfully to many ciphers and hash functions but new attack techniques are derived from it. We take advantage of the method and use it to analyse the block ciphers Threefish, PRESENT, HIGHT and LED and the hash functions WIDEA and SPONGENT.Our publications on LED and AES deal with the differential probability of AES-like block ciphers for a fixed key. Previously, specialists expected to observe a binomial distribution for a fixed differential when all possible keys are tested. However, it was shown for the AES block cipher that two-round differentials are very structured and the number of right pairs that satisfy the differential can be either a power of two or zero. In this thesis, the previous work is extended from two to four rounds and it is shown that a similar structure can still be observed.This thesis also studies lightweight symmetric-key algorithms. We analyse the security of PRESENT, HIGHT, LED and WIDEA and designed the hash function SPONGENT.nrpages: 190status: publishe