Low probability differentials and the cryptanalysis of full-round CLEFIA-128

Emami, Sareh, Ling, San, Nikolić, Ivica, Pieprzyk, Josef, & Wang, Huaxiong (2014) Low probability differentials and the cryptanalysis of full-round CLEFIA-128. Lecture Notes in Computer Science [Proceedings of the 20th International Conference on the Theory and Application of Cryptology and Information Security], 8873, pp. 141-157.

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Abstract

So far, low probability differentials for the key schedule of block ciphers have been used as a straightforward proof of security against related-key differential analysis. To achieve resistance, it is believed that for cipher with k-bit key it suffices the upper bound on the probability to be 2− k . Surprisingly, we show that this reasonable assumption is incorrect, and the probability should be (much) lower than 2− k . Our counter example is a related-key differential analysis of the well established block cipher CLEFIA-128. We show that although the key schedule of CLEFIA-128 prevents differentials with a probability higher than 2− 128, the linear part of the key schedule that produces the round keys, and the Feistel structure of the cipher, allow to exploit particularly chosen differentials with a probability as low as 2− 128. CLEFIA-128 has 214 such differentials, which translate to 214 pairs of weak keys. The probability of each differential is too low, but the weak keys have a special structure which allows with a divide-and-conquer approach to gain an advantage of 27 over generic analysis. We exploit the advantage and give a membership test for the weak-key class and provide analysis of the hashing modes. The proposed analysis has been tested with computer experiments on small-scale variants of CLEFIA-128. Our results do not threaten the practical use of CLEFIA.

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ID Code: 82452
Item Type: Journal Article
Refereed: Yes
Additional Information: Advances in Cryptology – ASIACRYPT 2014 : 20th International Conference on the Theory and Application of Cryptology and Information Security, Kaoshiung, Taiwan, R.O.C., December 7-11, 2014. Proceedings, Part I. Print ISBN 978-3-662-45610-1
Keywords: CLEFIA, Cryptanalysis, Weak keys, CRYPTREC, Differentials
DOI: 10.1007/978-3-662-45611-8_8
ISSN: 0302-9743
Divisions: Current > Schools > School of Electrical Engineering & Computer Science
Current > QUT Faculties and Divisions > Science & Engineering Faculty
Copyright Owner: Copyright 2014 International Association for Cryptologic Research
Copyright Statement: The final publication is available at Springer via http://dx.doi.org/10.1007/978-3-662-45611-8_8
Deposited On: 11 Mar 2015 23:18
Last Modified: 13 Mar 2015 09:58

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