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Related-key attacks on block ciphers

Darbuka, Aslı
One of the most important cryptographic primitives is the concept of block ciphers which yields confidentiality for data transmission in communication. Therefore, to be sure that confidentiality is provided, it is necessary to analyse the security of block ciphers by investigating their resistance to existing attacks. For this reason, related-key attacks gain much popularity in recent years and have been applied to many block ciphers with weak key schedules. In this work, our main motivation is to cover types of related-key attacks on block ciphers and exemplify them. \\ For years, cryptanalysts have been investigating the security of the block cipher XTEA and proposed several attacks on the cipher. First in FSE'02, Moon et al. presented a 14-round impossible differential attack on XTEA. Then in ICISC'03, Hong et al. proposed a 15-round differential attack and a 23-round truncated differential attack on XTEA. In FSE'04, Ko et al. proposed a 27-round related-key truncated differential attack on XTEA. Afterwards, in Vietcrypt'06, Lee et al. proposed a 34-round related-key rectangle attack on XTEA. Finally in 2008, Lu improved this attack to a related-key rectangle attack on 36-round XTEA which is the best attack on XTEA in terms of the number of attacked rounds. In this thesis, we also analyse differential properties of both structure and key schedule of XTEA block cipher and introduce our 25-round related-key impossible differential distinguisher for XTEA.