This thesis consists of an introductory part of how the symmetric cipher AES works in detail and how truncated differential cryptanalysis can be used to break some round reduced versions of AES. All the main attacks in this analysis has been successfully implemented using C#, and we have improved the overall data complexity of the attack from 2^11.3 ACC to roughly 2^10.59 ACC by doing some slight adjustment in the implementation of the attack. Chapter 1 gives a short introduction to the concepts within cryptography and the importance of cyber security in general. Chapter 2 gives an insight in how symmetric cryptosystems works and the design principles of block ciphers and SP-networks. Chapter 3 gives a detailed explanation of how the AES algorithm works. Chapter 4 gives an overview over existing attack methods that is applied on round reduces versions of AES. Chapter 5 lists all the cryptanalysis tools to perform the exchange attack on AES. The main attacks on 5 rounds for this thesis is described in Chapter 6 where we also add some self-made attacks based on the same principles of the main attacks. We list our conclusions and findings in Chapter 7.