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The subject of this thesis is the study of cryptographic hash functions. The importance of hash functions for protecting the authenticity of information is demonstrated. Applications include integrity protection, conventional message authentication and digital signatures. Theoretical results on cryptographic hash functions are reviewed. The information theoretic approach to authentication is described, and the practicality of schemes based on universal hash functions is studied. An overview is given of the complexity theoretic definitions and constructions. The main contribution of this thesis lies in the study of practical constructions for hash functions. A general model for hash functions is proposed and a taxonomy for attacks is presented. Then all schemes in the literature are divided into three classes: hash functions based on block ciphers, hash functions based on modular arithmetic and dedicated hash functions. An overview is given of existing attacks, new attacks are demonstrated, and new schemes are proposed. The study of basic building blocks of cryptographic hash functions leads to the study of the cryptographic properties of Boolean functions. New criteria are defined and functions satisfying new and existing criteria are studied.