Security of symmetric cryptosystems

Hash functions are cryptographic functions that process an arbitrary length input to a unique fixed length output. It is very difficult to determine the security limits of hash functions. In this thesis, the methods used to determine the security of hash functions, which are an element of symmetric cryptography, are explained. Cryptographic systems, which were selected by American Institute of Standards and Technology (NIST) in 2018 within the scope of lightweight cryptography project, were analyzed. In the first part of the thesis, information about symmetric cryptography and hash functions is given. Mathematical structures used in symmetric cryptography are defined. In the following sections, security definitions and cryptanalysis methods are given by investigating the general attacks on the hash functions by utilizing the systems containing the hash function selected in the NIST lightweight cryptography project.