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Cryptography 2019, 3(1), 4; https://doi.org/10.3390/cryptography3010004

# Cryptanalysis of Round-Reduced Fantomas, Robin and iSCREAM

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Institute of Computer Science, Polish Academy of Sciences, 01-248 Warsaw, Poland
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Department of Mathematics and Computer Science, Brandon University, Brandon, MB R7A 6A9, Canada
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Research Center for Interneural Computing, China Medical University, Taichung 40402, Taiwan
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Faculty of Mathematics, Informatics and Mechanics, University of Warsaw, 02-097 Warsaw, Poland
*
Author to whom correspondence should be addressed.
Received: 9 December 2018 / Revised: 31 December 2018 / Accepted: 7 January 2019 / Published: 10 January 2019
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# Abstract

In this work, we focus on LS-design ciphers Fantomas, Robin, and iSCREAM. LS-designs are a family of bitslice ciphers aimed at efficient masked implementations against side-channel analysis. We have analyzed Fantomas and Robin with a technique that previously has not been applied to both algorithms or linear cryptanalysis. The idea behind linear cryptanalysis is to build a linear characteristic that describes the relation between plaintext and ciphertext bits. Such a relationship should hold with probability 0.5 (bias is zero) for a secure cipher. Therefore, we try to find a linear characteristic between plaintext and ciphertext where bias is not equal to zero. This non-random behavior of cipher could be converted to some key-recovery attack. For Fantomas and Robin, we find 5 and 7-round linear characteristics. Using these characteristics, we attack both the ciphers with reduced rounds and recover the key for the same number of rounds. We also apply linear cryptanalysis to the famous CAESAR candidate iSCREAM and the closely related LS-design Robin. For iScream, we apply linear cryptanalysis to the round-reduced cipher and find a 7-round best linear characteristics. Based on those linear characteristics we extend the path in the related-key scenario for a higher number of rounds. View Full-Text
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

MDPI and ACS Style

Dwivedi, A.D.; Dhar, S.; Srivastava, G.; Singh, R. Cryptanalysis of Round-Reduced Fantomas, Robin and iSCREAM. Cryptography 2019, 3, 4.

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