Differential factors and differential cryptanalysis of block cipher pride

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Tezin Türü: Yüksek Lisans

Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Enformatik Enstitüsü, Bilişim Sistemleri Anabilim Dalı, Türkiye

Tezin Onay Tarihi: 2017

Öğrenci: EROL DOĞAN

Eş Danışman: CİHANGİR TEZCAN

Danışman: SEVGİ ÖZKAN YILDIRIM

Özet:

Today, IoT devices are used in very critical areas like payment cards, contactless keys and biometric authentication. Moreover, while the number of IoT Technologies increases, cryptographic systems that are optimized for IoT devices that require less cost, less power, and less memory are highly required in today’s industry. Therefore, in recent years several lightweight block ciphers are published to satisfy industry needs. However, there are still more work needed to be sure about the security of these block ciphers. Differential cryptanalysis is one of the important methods used in block cipher analysis. This method deals with how minor differences made in the plaintext can lead to certain differences in the cipher text. It is examined that whether the expected differences are observed or not by testing all candidate key bits on a number of plaintextciphertext pairs. The correct key is expected to provide these differences more times than the wrong keys. By this means the correct key is captured. However, a recent study, Differential Factors showed that it may not be possible to fully capture the attacked round key bits when performing a differential attack. Besides, another recent study Undisturbed Bits can be used for discovering longer differential characteristics that provides opportunity for more powerful differential attacks. Inthisthesis,wehaveinvestigatedseverallightweightblockciphersfortheexistence vi of Differential Factors and Undisturbed Bits. We have also shown how differential factors can be used to reduce the time complexity of differential attacks by summarizing the corrected attacks on PRESENT and SERPENT block ciphers. Moreover, we have also investigated the 18-round, 19-round and 20-round differential attacks on PRIDE block cipher and we have corrected these attacks considering differential factors. As a result, by our correction we have shown that these attacks require more time complexity than they were claimed.