Impossible Differential Cryptanalysis of Fantomas and Robin

Xuan SHEN  Guoqiang LIU  Chao LI  Longjiang QU  

IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E101-A   No.5   pp.863-866
Publication Date: 2018/05/01
Online ISSN: 1745-1337
DOI: 10.1587/transfun.E101.A.863
Type of Manuscript: LETTER
Category: Cryptography and Information Security
block cipher,  LS-designs,  Fantomas,  Robin,  impossible differential cryptanalysis,  

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At FSE 2014, Grosso et al. proposed LS-designs which are a family of bitslice ciphers aiming at efficient masked implementations against side-channel analysis. They also presented two specific LS-designs, namely the non-involutive cipher Fantomas and the involutive cipher Robin. The designers claimed that the longest impossible differentials of these two ciphers only span 3 rounds. In this paper, for the two ciphers, we construct 4-round impossible differentials which are one round more than the longest impossible differentials found by the designers. Furthermore, with the 4-round impossible differentials, we propose impossible differential attacks on Fantomas and Robin reduced to 6 rounds (out of the full 12/16 rounds). Both of the attacks need 2119 chosen plaintexts and 2101.81 6-round encryptions.